# What would cause a diesel engine to run cool?



## julied (Jun 7, 2000)

I have a Westerbeke 70 hp diesel that should be running between 170 and 190 degrees but instead is only getting up to 150 degrees. What would cause a diesel to run cool? I changed the thermostat (operating temperature is 180), I checked the coolant level and even checked to make sure that the temperature gauge was working properly. No problems with any of them. 

What are the consequenses of a cool engine? More fuel being consumed?

I GOT AN ANSWER TO MY QUESTION FROM THE MECHANIC THAT I HIRED. THE WESTERBEKE 70 HAS A FLOWCONTROLLER AT THE END OF THE MANIFOLD. THE FLOWCONTROLLER HAD GONE BAD AND WASN'T ROUTING THE COOLANT PROPERLY. ONE SIDE OF THE MANIFOLD WAS RUNNING AT 175, THE OTHER 140, ALL BECAUSE OF THE FLOW CONTROLLER, WHICH THE WESTERBEKE DEALER SAID RARELY POSES PROBLEMS. 

THANKS FOR EVERYBODYS HELP AND SUGGESTIONS. IT'S GREAT TO HAVE YOU ALL TO RUN THINGS PAST.


----------



## buddabelly (Sep 21, 2007)

*Running cool*

I can make mine run cool or hot by adjusting the ball valve in the recirculating line on my 5411. On mine the water recirculates until the thermostat opens then sends it out the exhaust. When valve is all the way open the water takes the path of least resistance and continues to recirculate and very little goes out the exhaust. As I close off the valve the water is less able to recirculate and more water goes out the exhaust and the motor runs cooler. I need to adjust the valve through out the year as the water temp increases.


----------



## erps (Aug 2, 2006)

Sounds like julied has fresh water cooling, as it was mentioned that the coolant level was checked. How was the accuracy of the temperature guage checked? Also, maybe the thermostat isn't sealing well so enough water leaks by to keep it from warming up? I frankly don't think that running at 150 degrees vs. 170 degrees will make that much of a difference, but I'm a backyard mechanic, not a diesel expert.


----------



## julied (Jun 7, 2000)

We checked the temperature guage by dipping an engine thermometer through the radiator cap and then warming the engine up. We checked the temp of the coolant and the temp on the engines temp guage every 5 minutes for about 1/2 and hour. They only read about 5 degrees different which I understand is okay since the coolant temp will be different in different areas of the engine.

We changed the thermostat and the gasket yesterday. We've got a good seal.

I'm not sure that I actually do have a problem but my engine manual says to make sure it runs between 170 and 190. I didn't even realize that there might be a problem until tracing a problem with our hot water heater which is not heating efficiently off the engine.


----------



## Maine Sail (Jan 6, 2003)

*There is no better*

There is no better device for troubleshooting engine cooling issues than an infrared thermometer. Simply aim and pull the trigger and it tells you the temp.. Get one and you'll be amazed at all the uses you find for it. Ignore the price at that link, it's the first one I came across, as you can pay a LOT less money for them than $99.00...

Infrared Thermometer


----------



## Stillraining (Jan 11, 2008)

What was the rating on the new thermostat?


----------



## camaraderie (May 22, 2002)

You may have a loss of compression causing it not to come up to full temp.
Cool temps can be the equivilent of idling the diesel for extended periods which can be damaging as follows:

*This is because the engine is not allowed to reach operating temperature, where harmful combustion by-products are eliminated. This acidic by-product accumulates in the oil, where it chemically attacks the engine bearings.

Here's what happens when a diesel engine is idled:
* 
*Timing gear backlash [gear rattle] is maximized, leading to increased wear*
*The cylinders get glazed, leading to low compression*
*The engine is run at below operating temp, leading to carbon accumulation in the combustion chamber, injector tips, piston rings, piston crown, valves heads, seats, and stems, exhaust manifold, turbocharger, etc. Carbon on these parts will lead to accelerated wear, and possible piston ring sticking and low engine compression.*
*Also, the injected fuel gets past the piston rings, because the engine is not at the correct temperature, and dilutes the lube oil. This compromised oil is sent to ALL the engine bearings, where it increases bearing wear.
*
* There's more, but isn't this enough to convince one that engine idling should be avoided?

Yanmar [for one] says not to idle their engines for more than 5 minutes. Bottom line on engine idling - it's great for the engine repair business.

*If you've checked out the obvious issues...get it to a mechanic before you really end up with a big bill.


----------



## erps (Aug 2, 2006)

The fact that you've introduced a hot water heater to the cooling circut may have changed things. Depending on where you tapped into the fresh water cooling circut, you may have taken the thermostat out of the loop inadvertantly. So even though the thermostat is closed, limiting the amount of water going to the heat exchanger, you may be sending it to the heat exchanger in your hot water heater instead. You could troubleshoot that by pinching/closing off the loop to the hot water heater and see if you get up to operating temperature then.

Also, the temperature of the coolant in the heat exchanger should be lower than the coolant temperature in the engine, because it's in contact with the cold raw water in the heat exchanger tubes. That's what the heat exchanger does, cools the fresh water down. I'd bet a buck that your hot water heater is probably involved.


----------



## Stillraining (Jan 11, 2008)

Good point Ray...I didnt think of that..


----------



## timebandit (Sep 18, 2002)

Pull the thermostat and place in a pan with water and use your thermometer to see where it is opening. The thermostat is what controls the temp of the motor. When you have it out look at the bottom of the pill and the temp should be stamped there. 
If the water is very cold and the flange on the thermostat has a small bleeder hole that may be enuff to keep the enngine from comming up to temp. 
If the test show the thermostat is opening ok then pru a pop rivet in the hole.


----------



## Valiente (Jun 16, 2006)

Nine posts since 2000? This is not a person who asks for help often!

Another point to add to your mulling: Today I ran my old boat from one yacht club to another to do a repair. The Atomic 4 has the fresh water thermostat rated at 180F (good for the engine, but too hot for salt water, where it throws a deposit, and where the 'stat is rated 140F). Anyway, I was cruising at five knots for an hour, and I couldn't see the engine temp get above 145 F.

Then it struck me: The water temperature in Lake Ontario in May is about 9 C/ 45 F. That's pretty cold water going through the block. By July, it will be 21 C/70 F and I'll be getting readings of 175 F and presumably, the thermostat will be mostly open.

Could it be that the raw water cooling circuit is quite cold at the moment, meaning the engine coolant can't warm up unless that circuit is restricted?

The hot water circuit might be at issue, but it really depends on how it's plumbed. Mine not yet connected into the engine, which is coming out for inspection, but I am assuming that it is the raw water circuit that is heated by the coolant (in turn heated by engine heat) which in turn transfers heat to the potable water in the hot water tank. Otherwise, you'd run the coolant itself through the coils in the hot water tank, and that would be a little dangerous. A failure of the raw water circuit...post-heat exchanger...would be noticeable by the lack of water at the exhaust, the change in engine note, and water in the bilge....nasty but fixable if noted before things post mixing elbow start melting.


----------



## MedSailor (Mar 30, 2008)

So I'm not an expert, but I'll throw a few things into the mix:

The thermostat's job is to restrict cooling water for a while until the engine warms up, after that it opens and allows maximal cooling. This is to speed warm up and no thermostat is designed to close off at cruising or max rpm it's function should not affect your max operating temp. 

If you do want to check the thermostat remove it, put in in a pot of water on the stove and turn it on. Have a thermometer in the pot and record the temp when it pops open.

But, the thermostat isn't the problem is is it? Are you reaching your rated RPM? If you're lugging your engine (running it under rated rpm) you will run cold and have all the problems already listed. Currently we aren't getting up to rated rpm and this summer we're going to troubleshoot this very problem. 

Any of these problems can cause you not to reach RMP:
If your fuel is old or restricted
If your throttle cable is not at full travel
If your prop is too large or has too much pitch
If your racor filter element is too fine

Poor engine/prop selection is often the cause. Even the Dashews recommend a large prop turning slowly for "fuel economy". I've know people who repowered to get this effect at the expense of their engine.

Medsailor


----------



## julied (Jun 7, 2000)

Thanks for all the great suggestions! A couple of things: the water heater is not new, nor has it been changed. It's just the first thing that we noticed was wrong. I think we are not getting efficient water heating because the engine is running so cool. 

I bought a new thermostat from Westerbeke. Used the one called out in the manual (180 degree operating temp). We replaced it one Friday and today tested the old one. It opened at 180 degrees, just as it is rated. So I guess I've got a spare!

Wasn't positive that I had a real problem be am obviously concerned. I'm going to take Camaraderies advice and call a mechanic tomorrow. Hope my bank account can handle it...

Hopefully getting the temp up to an appropriate temp will take care of my inefficient water heater too! (fingers crossed)


----------



## MedSailor (Mar 30, 2008)

Let me know what you find out. I have a similar issue.
MedSailor


----------



## Rockter (Sep 11, 2006)

I reckon the thermostat is stuck open. That would do it.


----------



## timebandit (Sep 18, 2002)

MedSailor said:


> So I'm not an expert, but I'll throw a few things into the mix:
> 
> The thermostat's job is to restrict cooling water for a while until the engine warms up, after that it opens and allows maximal cooling. This is to speed warm up and no thermostat is designed to close off at cruising or max rpm it's function should not affect your max operating temp.
> 
> Medsailor


The job of the thermostat is to open and close constantly to change the water flow to keep the engine at a cirtain temp.
If the engine is running hard and creating lots of heat it may open max and then close to a mim at an idle in neututral.


----------



## julied (Jun 7, 2000)

Guess I've done all I can to try to figure this out on my own. Replaced the thermostat, tested the old one (it was fine), tested the temp gauge... Now I've got an appointment in a couple of weeks with a Westerbeke mechanic. I'll post the findings.


----------



## camaraderie (May 22, 2002)

Quite a wait for a mechanic! Good luck...look forward to hearing the diagnosis.


----------



## Plumper (Nov 21, 2007)

My engine has a loop in the cooling system for the hot water heater. When I have the valve open, allowing the engine to heat the water in the hot water tank, the engine runs about 10 degrees C hotter. When I close that valve, isolating the hot water tank, the engine runs cool. Perhaps your system has a similar setup.


----------



## KeelHaulin (Mar 7, 2006)

camaraderie said:


> You may have a loss of compression causing it not to come up to full temp.


If that were true; the engine would be very difficult to start. Likely to the extent that starting fluid would be required to get it to fire up.



> Cool temps can be the equivilent of idling the diesel for extended periods


Well; no. At idle there is no shaft loading so gear backlash can occur (with related long term wear) and the other issues of carbon build-up etc are probably not going to happen if the engine is only running 20deg F cooler. The main effect would probably be a bit lower fuel efficiency while cruising.



> *This is because the engine is not allowed to reach operating temperature, where harmful combustion by-products are eliminated. This acidic by-product accumulates in the oil, where it chemically attacks the engine bearings.*
> 
> _*Here's what happens when a diesel engine is idled:*_
> 
> ...


Hmm... Where was that list of problems associated with idling taken from? I'd like to know why this is such a big issue with Diesel sailboat engines and not all of the other Diesel engines on the planet (cars, trucks, tractors, ships, etc). Many of these engines idle for long periods of time while waiting for their next task. In cold northern climates Diesels are left running to prevent/minimize cold starting and bearing friction while starting up.

Cylinder glazing is not very common; I think if it happens you have other engine issues (like poor compression) to begin with. The same goes for carbon build-up and fuel getting into the oil. These are all issues that are associated with an engine that is getting near the end of it's service life (in need of a rebuild) and IMHO are not directly associated with allowing an engine to run at idle for more than 5 minutes.

What do cruising sailors do who want to re-charge batteries? Yes, I know solar panels and wind generators, etc. But what about situations where the engine alternator is needed?

Overheating a Diesel is much more damaging than over-cooling. If it were me I would take the boat out (after warming up at the dock); run it up to Max cruising RPM and let it run there for 1/2 hour or so. Then check the engine temp on the gauge and at the header tank and decide if it truly is over-cooling. If you don't run it at max cruising RPM you won't know if the engine is ever getting warm enough to open the thermostat. 150 F would indicate that it just is not generating enough heat to need additional cooling via the heat exchanger. In general marine diesels tend to get calcium build-up in the heat exchanger; then overheat unexpectedly when put under a load. If your engine is normally running a bit cool (and does not overheat when under a load) you might be better off in the long run.

JMHO/HTH...


----------



## camaraderie (May 22, 2002)

Extended idling of a marine diesel is a well discussed topic and universally acknowledged by Yanmar, Calder, and others as being bad for the engine. this is one of the reasons why so many people add passive and generators...to avoid damage to their main engine. My own approach before my current boat was to use passive as much as possible...take advantage of motoring under power to charge the batteries and finally to run the engine at idle for as little time as possible with as BIG an alternator as possible (without bearing problems) to maximize the load and minimize run time. The quotes above were taken from JoeDeMers who runs this site along with his marine diesel repair business:
Sound Marine Diesel LLC Q and A

No argument that heat damages many more engines as that can happen quite quickly and the cold running problem is more insidious and takes time.


----------



## KeelHaulin (Mar 7, 2006)

Okay... What is the difference between a marine diesel and a non-marine diesel? It might also be that sailboat engines never get loaded correctly while motoring due to reduced hull drag and small (drag reducing) props. The motor may never really see a full load in it's entire service life and that would account for problems like carbon build-up and glazing.

I still advocate letting your engine warm-up and cool down at idle when you arrive/leave from the dock. The biggest engine wear factor (aside from overheating) in Diesels is starting friction; because of the high compression loads and loss of oil pressure while starting. I'd say that sailboats are more prone to starting wear because of the need to motor for short periods if the wind becomes light. The need to run the engine for daily charging needs will also have an effect and is a good reason to invest in solar and/or wind generators.

Again to julied's problem; be sure that it is not just a normal operating range when the engine is not under heavy load. Check to be sure you have the correct coolant/water ratio because that can make a difference in cooling efficiency. Shut off the water heater circuit to isolate the engine cooling circuit and eliminate a source of cooling.


----------



## sailingdog (Mar 19, 2006)

Keelhaulin-

Marine engines tend to have harder lives than non-marine ones... Once a car or truck gets rolling, inertia helps keep it rolling, and the amount of resistance that the engine has to over come is rather minimal. A boat, especially a heavy displacement design, like a monohull sailboat, is generally going to have a lot of resistance due to the friction generated by the water.


----------



## Maine Sail (Jan 6, 2003)

We never did hear how he trouble shot the temp gauge and determined it to be the correct temp. Seeing as I have had this happen to me, temp gauge reading low, it is not out of the question. 

P.S. Living in Maine, the land of the ever idling diesel, in the winter, I often wonder why big rigs, school buses, box trucks, contractors diesel pick up trucks & vans, back hoes, skid steers and the like do not glaze over but my small marine diesel will? 

My small engine has a huge alternator, in comparison to a 200 horsepower diesel pick up truck, that is capable of robbing up to 15 to 20% of the available horsepower? How again is that not considered a load on a marine diesel but the pick up truck can idle all winter with no issues..??

If anyone has a good answer as to why a big rig or any diesel other than marine can idle all winter long and not have glazing issues but my marine diesel, with a 1-4hp robbing (load) alternator will, please fill me in??


----------



## KeelHaulin (Mar 7, 2006)

SD-

I think it's the contrary; a diesel tractor, truck, car all are under much more load when accelerating or plowing a field, etc. Diesel engines are primarily designed to produce high torques at low RPM's and I just can't see where the torque resistance is going to be generated on a relatively small diameter (undersized in general) sailboat prop.

Halekai-

Yeah; that's what I've been wondering. How is it that so many other Diesel engines don't suffer from the problems associated with idling while for some reason a sailboat engine is more prone to these damaging effects that are blamed on running at idle for too long? I think it's more due to the improper maintenance by owners who don't know very much about engines to begin with that lead to problems like carbon build-up, low compression, glazing, etc.; and the blame gets placed on the myth that allowing the engine to idle too long was the culprit.

Of course if you run your engine daily to charge batteries; and never leave your mooring or otherwise put the engine under load you may very well get carbon deposits, and glazed cylinders. It's a matter of how the engine has been run (and maintained) in an overall sense that determines it's longevity.


----------



## artbyjody (Jan 4, 2008)

I have often wondered the same, so what makes the difference?

I'll tackle this from my F-350 experience.

1. Cooling is a closed system not effected by environmental factors other than temp.

Marine systems - cooling is dual and water can back into engine. I would recond to think that at some point all marine engines have water in the system.

2. Why is the above important, because the engine is an open system if you look at the big picture. Which means that sea water can actually get back into the fuel system - introducing the various microbes and algae.

3. Diesels we drive or use as tools (farming etc...)- are usually 6 - 8 cylinders and on average significantly larger. Which means when compression takes places there is more muscle. A typical Yanmar - 3 cyl - the engine is about 1/5 the scale of their other counterparts. This means more actual energy expelled which means you can have more contaminated fuel, but the engine forces can expel the waste and burn the residual fuel more efficiently. 

I drive my F-350 maybe 10 times a year yet less than the low temperature startup - usually goes right over... and thus the only things I can detract from the differences are the above..


----------



## RXBOT (Sep 7, 2007)

*Marine engine loading*

Pushing a displacement hull through water is similar 2 driving a truck up steep mountain. Steady heavy load. Running 2 cool? Is cooling warer circulating all the time & so cold engine never gets up to temp ?


----------



## Idiens (Jan 9, 2007)

I'll go with the theory that the engine is fine and dandy. The thermostat bypass is carrying enough water, the cooling capacity is scaled to a hot climate and is operated in a cold one.


----------



## Omatako (Sep 14, 2003)

Idiens said:


> I'll go with the theory that the engine is fine and dandy. The thermostat bypass is carrying enough water, the cooling capacity is scaled to a hot climate and is operated in a cold one.


The "cooling capacity" has nothing to do with anything. When compared to a automotive system, your boat has a cooling system of 200 squillion litres of water (the sea, the whole sea and nothing but the sea). What regulates the temp in the system is plain and simple - the thermostat does. No matter how much coolant you have or how big the heat exchanger is, the temp set on the thermostat will, if it is working right, keep the engine at the correct temp.

In this case since the thermostat is new we are assuming that it is OK. Wrong. Many thermostats are incorrect at manufacture compared to the grading. Also, nobody so far has said that the correct thermostat was fitted. Could be the wrong one.

But I do agree with one statement above - the engine is OK. Any real problem with the coolant would cause it to run hot, not cold. But it is necessary to get it right because cold engines wear much quicker than hot ones. And besides, luke warm showers suck.

And another sacred cow slaughtered (IMHO). There is no truth in the fact that idling engines glaze quicker. I have worked for decades with heavy vehicles and know of many applications where truck engines idle for long periods and those engines are still good for well over a million miles. In the Siberian regions trucks are idled right through the night while the driver sleeps because if it is turned off the oil in the crankcase freezes. Excessive idling will cause sooting and other irregularities IF the engine is on poor condition to begin with.

Andre


----------



## Idiens (Jan 9, 2007)

Andre - most of the engines I know have a bypass channel around the thermostat. This ensures that the coolant circulates even when the thermostat is completely closed. In this state, the engine warms up quickly, but a bit slower if the calorifier is in the same loop. At some point the thermostat sees enough heat to start opening and start to pass hot water through the heat exchanger. It may be seeing hotter water than the temperature sensor does. If the heat exchanger is very efficient, perhaps because it gets very cold raw water, it can work with a fraction of the thermostat's flow capacity. The temperature at which the thermostat starts to open and that which holds it fully open are different.

As you say, overheating it the real problem. In that case, the flow rates in both cooling circuits, with the thermostat full open and the heat exchanger having to work with warm tropical water have to be designed adequate to hold down the temperature. So it is usually over capable for temperate climates.

An engine is also cooled by oil circulation and there is usually an oil cooler, sometimes (like my old MD21A) on the raw water cooling system. Again, this cooler is designed based on the peak cooling requirement, so it has spare capacity at lower ambient temperatures and hence lowers the oil temperature accordingly.


----------



## Idiens (Jan 9, 2007)

Actually, julied - to test my theory, try running the engine with the thermostat removed. If I am right, it should run at a lower temperature than with the thermostat in place. In my theory, your thermostat is hardly opening.


----------



## Omatako (Sep 14, 2003)

Idiens said:


> Actually, julied - to test my theory, try running the engine with the thermostat removed. If I am right, it should run at a lower temperature than with the thermostat in place. In my theory, your thermostat is hardly opening.


Sorry to be a PITA. If the thermostat was sticking closed the engine would run hot, not cold.

Andre


----------



## Idiens (Jan 9, 2007)

Omatako said:


> Sorry to be a PITA. If the thermostat was sticking closed the engine would run hot, not cold.
> 
> Andre


Dear PITA, Did I suggest is was sticking? Did I suggest that the engine would run hotter with the thermostat removed?


----------



## Omatako (Sep 14, 2003)

Idiens said:


> Dear PITA, Did I suggest is was sticking?


Actually, to me, yes you did.

By saying "in my theory, the thermostat was hardly opening" that sort of evokes the image of sticking (at least to me it does). That would create a situation where the engine runs hotter.

The OP is complaining that the engine is running too cool.

Once again, I seem to be missing the point (and the need to insult, smiley face or no).

Andre (as opposed to PITA)


----------



## KeelHaulin (Mar 7, 2006)

What Idiens is trying to say is that the engine would likely be running much cooler than 150 if the thermostat were not doing something; and/or much hotter if the thermostat is not opening at all. So one way to test it is to run the engine without the thermostat to check for overcooling (IE the engine never comes up above 110 or so with the thermostat removed).

My Perkins 4-108 runs on the cool side when running at slow speeds or idle/warm-up. The temp goes up to 175 or so when the engine is running at cruising RPM and it cools back down when not motoring at hull speed. I really think the temp should be checked when the engine is under a continuous load; not while at the dock.

Some people install a diverter so that the engine gets less flow in cold climates; but I really don't think you need this if you are running at 150 when idle or under a light load.


----------



## Idiens (Jan 9, 2007)

Sorry Andre, I was just picking up from your own statement:-



Omatako said:


> Sorry to be a PITA. .....


I was not trying to be hurtful, hence the smiley.

All the thermostats I have seen start to open at one temperature and are fully open at a higher temperature. Between the two temperatures, the flow through the thermostat increases from very little to as much as the circulation pump can achieve. If the OP's engine is being cooled efficiently somewhere between these two temperatures, the thermostat balances at that point. I don't think it could be described as sticking at that point, in the sense that it would not open further, if the temperature rises further.

An engine thermostat is designed to control to a certain temperature.

The other point I tried to make is that the temperature gauge sensor and the thermostat might be measuring different water temperatures, depending on their location. So even though they can both be tested in a pan of water being brought up to the boil, they can disagree when mounted in the engine.


----------



## billyruffn (Sep 21, 2004)

Is this an engine you know well (ie a new problem), or is this a new boat? 

Here's one possibility, albeit a tad far fetched: I had a French mechanic tell me that my Nanni diesel was a "cold water model" and that was the reason it was getting too hot in the tropics. Apparently the difference between cold water and warm water cooling systems is the size (length) of the collar that wraps around the tube stack. If you have a 'warm water' cooling system and are operating in cold water......?????? Ask Westerbeke. My guess is that only a French engine would have an option for a hot or cold cooling system.


----------



## jimgorgon (Jun 7, 2021)

This is a fascinating thread. It gets to the heart of my problem with a volvo md2030. Pl lol p i’ll


----------



## jimgorgon (Jun 7, 2021)

jimgorgon said:


> This is a fascinating thread. It gets to the heart of my problem with a volvo md2030. Pl lol p i'll


apologies I'm on my phone and was interrupted.

The engine should run around 180 F. 82C but only gets up to 130 F 55C. Mostly likely would be an inaccurate gauge but I used a tester and the gauge is fine 
OR that the thermostat is stuck open. I replaced the thermo with a new one I tested and still - the engine running too cold. still at 130.

I'm stumped. Is it possible that the engine itself never makes it up to operating temp?

thanks


----------



## SchockT (May 21, 2012)

On my old Volvo MD7a there was a bypass passage that allowed some cooling water to go around the thermostat. Perhaps you have something similar on your engine?

What is the temperature rating of the thermostat? You can get them in different temp ranges. It should be marked on the thermostat, but you can test it by heating it up in a pot of water and checking the temperature when it opens.

Is water going around the thermostat due to improperly seated or missing gasket?



Sent from my SM-G981W using Tapatalk


----------

