# How hot does your diesel run?



## tspooner (Jun 18, 2011)

A few weeks ago I posted a cooling question and received a lot of good responses from a lot of good people on this forum. I had installed a water temperature gauge for my Yanmar 2GMF to better judge how hot the running temperature was versus the original alarm set up. The guage issue was indeed a result of the supplier selling me the wrong sending unit. After checking all water delivery systems, both salt & fresh I feel confident that the flow is working as it should. After about 20 minutes of running the engine at the dock under load the temperature guage is showing about 185 degrees. The infrared gauge is showing around 178 degrees when pointed at the cylinder head near the injectors. I'm tired of just using the motor to get in and out of my slip for daysails and was still hoping to get away for a week of sailing up the coast. However I'm paranoid about having to use the engine for extended periods if the wind doesn't show up! These readings seem high and are a concern to me. Does this seem right to you? How hot are these diesels supposed to run?


----------



## johnnyquest37 (Feb 16, 2012)

My M-35B runs between 160 and 180, according to the temp. gauge at the helm.


----------



## Tim R. (Mar 23, 2003)

178° at the cylinder head is fine. What temp do you get when you point it at the top of the thermostat housing? That is the most accurate reading you will get of the fresh water side. You could be running normally if you have a 180° thermostat installed.


----------



## eherlihy (Jan 2, 2007)

My Universal M25 runs at 180ºF exactly.

A couple of weeks ago I was motorsailing through heavy chop in 'Vineyard Sound (trying to get to Cuttyhunk before dark), and did not realize that the angle of heel on starboard tack was great enough to partially lift the intake out of the water. After about an hour, I heard the "beep, beep, beep..." of the temperature alert (for the fist time ever), and quickly shut down the engine. I looked at the temp gauge, and it was no more than 185ºF. I checked the coolant level (which was high), oil level, raw water strainer, and the impeller, and found that all was OK. We changed tack, and sailed in to the outer harbor. I started the engine to get into the inner harbor, and all worked as it should.

I am glad to have both an audible alarm and a gauge.


----------



## Bradhamlet (Nov 8, 2002)

Each Yanmar is different, my 3GM is raw water cooled and the alarm starts buzzing when over 150 however some fresh water cooled motors will buzz their alarm at 200. So You might call a Yanmar tec to find out what yours will buzz at.

Brad 
Lancer 36


----------



## Tim R. (Mar 23, 2003)

eherlihy said:


> My Universal M25 runs at 180ºF exactly.
> 
> A couple of weeks ago I was motorsailing through heavy chop in 'Vineyard Sound (trying to get to Cuttyhunk before dark), and did not realize that the angle of heel on starboard tack was great enough to partially lift the intake out of the water. After about an hour, I heard the "beep, beep, beep..." of the temperature alert (for the fist time ever), and quickly shut down the engine. I looked at the temp gauge, and it was no more than 185ºF. I checked the coolant level (which was high), oil level, raw water strainer, and the impeller, and found that all was OK. We changed tack, and sailed in to the outer harbor. I started the engine to get into the inner harbor, and all worked as it should.
> 
> I am glad to have both an audible alarm and a gauge.


Ed, you should verify your gauges accuracy before assuming it is correct.


----------



## capta (Jun 27, 2011)

The important thing to remember with temp gauges is that they may not be an exact reading of the true temp (off even 10 or 15 degrees), but the changes are very significant. For instance, once the thermostat has opened it should come up to a normal operating temp (usually 180ish) and remain there. If the temp fluctuates w/ a change in RPM's, dropping at lower RPM's or rising as you go up, you have a cooling problem. If it begins to creep up (not in a day but over successive trips) from whatever is the normal operating temp, your impeller has probably lost a few vanes.
After a bit of time you will have a good idea of your normal operating temp reading on the gauge and can keep an eye out for changes. Your engine should run at the same temp for half an hour or 20 hours; time should make no difference.
There are odd times, usually in extreme conditions, where the engine is working much harder than usual and the temp can go up a few degrees, but it should never go above 200 (from 180ish), no matter what. I hope you also have an audible alarm, because a plastic bag or something else could cause a blockage in the line and the temp will go up very quickly to damaging levels, unnoticed on the gauge.


----------



## Omatako (Sep 14, 2003)

Tim R. said:


> You could be running normally if you have a 180° thermostat installed.


That is the intelligent answer.

What thermostat is installed? If it is a 180°F then that's where the engine ought to run.

Most engines, marine or otherwise run at around 85°C (185°F, sorry I am metricated ) as controlled by their thermostats.

Closed circuit cooling systems can run hotter because they are pressurised and the boiling point of water is higher when under pressure. As a general statement, engines run more efficiently the hotter they run which is the primary reason for pressurised cooling systems. Raw water cooled engines will run on a cooler thermostat because there is no pressure but they should still run at the temperature regulated by the thermostat. Lesson over.

So if your engine is running at considerably less than 185° (or whatever the rating of your thermostat) then you should be concerned because it is less efficient and is probably experiencing accelerated wear. And your thermostat has either been removed or is stuck open.


----------



## overbored (Oct 8, 2010)

both raw water and recirculated water cooled engine run at the same internal temperature
they both burn diesel. the metals used are the same and the oil is the same. in fact they are the same engines. the reason they run a lower temp thermostat in the raw water cooled engines is because the thermostat needs to open and start letting in raw water at a lower temp so the metals will not be allowed to heat up to high and then get shock cooled by the cold raw water. on a 2GMF the thermo is set to start opening at 159 and full open at 185 degrees F. the raw water models use a 108 to 125 degree F thermostat


----------



## Seaduction (Oct 24, 2011)

'FRESH' WATER SYSTEM


----------



## npettett (May 30, 2006)

My M3-20B is showing 160 degrees at 1400 rpm pushing a CAT30 on a dead calm 85 degree day.


----------



## dvuyxx (Jun 23, 2009)

Our 1979 Westerbeke 30 (Four-91) runs at 180' at moderate to high cruising speeds. If you push it hard on full throttle for too long it gets just slightly hotter. If you pull it down just slightly below full, it jumps right back to 180.


----------



## tspooner (Jun 18, 2011)

Tim R. said:


> 178° at the cylinder head is fine. What temp do you get when you point it at the top of the thermostat housing? That is the most accurate reading you will get of the fresh water side. You could be running normally if you have a 180° thermostat installed.


The new thermostat is sitting on my nav table while I try to sort out whether I have a problem or not. Back to the boat yesterday to take some infrared readings and notes so I wasn't relying on a poor memory. The gauge has no increments between 180-240 degrees so it's a guess to what it is actually reading. After 20 minutes of running the engine @ 2000 rpm under load the gauge read approx 185, the infrared reading at the base of the thermostat housing was 175, cylinder head was 175: After 25 minutes gauge was approx 190, thermostat 181, cylinder head 180: After 30 minutes gauge was approx 210, thermostat 187, cylinder head 187. That was enough for me. I idled the motor for 5 more minutes and shut her down. There is steam coming from the exhaust and although I've noticed this in large cruising powerboats before I've never noticed much if any from my boat in the past. I've removed all hoses and ensured they are not blocked. The impeller checked out OK as did the FW cooling pump. The only thing I haven't removed is the cast iron riser where the exhaust gasses and spent salt water combine. I imagine there must be some blockage at that point. I'm convinced from what others have reported for temperatures and my own readings that I definitely have a problem.


----------



## zeehag (Nov 16, 2008)

perkie ran at 180 or just under---even when bashing against current from zihuatenejo to barra de navidad.. my ericson has 2qm20h which runs very cool to downright cold. even under load.


----------



## saillife (Jun 25, 2006)

Having had other problems with my engine I've been monitoring the engine temp for several months now (fresh water cooled 3GMF). The temp at the top of the thermostat housing using an infrared thermometer runs ~185. Sounds to me like your engine is running fine temp wise.


----------



## overbored (Oct 8, 2010)

tspooner said:


> The new thermostat is sitting on my nav table while I try to sort out whether I have a problem or not. Back to the boat yesterday to take some infrared readings and notes so I wasn't relying on a poor memory. The gauge has no increments between 180-240 degrees so it's a guess to what it is actually reading. After 20 minutes of running the engine @ 2000 rpm under load the gauge read approx 185, the infrared reading at the base of the thermostat housing was 175, cylinder head was 175: After 25 minutes gauge was approx 190, thermostat 181, cylinder head 180: After 30 minutes gauge was approx 210, thermostat 187, cylinder head 187. That was enough for me. I idled the motor for 5 more minutes and shut her down. There is steam coming from the exhaust and although I've noticed this in large cruising powerboats before I've never noticed much if any from my boat in the past. I've removed all hoses and ensured they are not blocked. The impeller checked out OK as did the FW cooling pump. The only thing I haven't removed is the cast iron riser where the exhaust gasses and spent salt water combine. I imagine there must be some blockage at that point. I'm convinced from what others have reported for temperatures and my own readings that I definitely have a problem.


you are getting steam from the sea water at the exhaust elbow this means it is starting to get plugged. the exhaust gas temp is constant, sea water temp is constant so the only way to make steam is to slow down the flow of sea water. if something was plugged on the fresh water side the sea water would be cooler when it reached the exhaust elbow and would not make steam. when ever there is cooling problem check the impellers first and then the exhaust elbow.


----------

