What's normal temperature what's not

kloudie1 · Jul 11, 2017

The metal thermostat housing on top of the engine where the short hose connects to the heat-ex housing.. That temp should be same as the thermostat rating.. or close to it.. Using a temp gun, it will register 10 or so degrees F less than thermostat rating since it is measuring the housing paint temp.. Your thermostat is a "160 F" nominal.. It is fully open at 185 F..

heritage · Jul 14, 2017

My prior boat had a 3gm30f that had a temp guage that would always run around 180-185 at cruise speed. Then it began to hit 190 and higher until I brought the rpms down. Clogging of the exhaust elbow was causing reduced raw water and exhaust flow. New elbow brought temp back to 180. My point to you is to look for a change in temp reading from your infrared gun. Kloundies suggestion to aim it at the thermostat housing is good,, just make sure you average the readings and aim at the same spot when taking future readings. You should also run your checks when at cruise speed because an elbow problem will not be apparent when there is low water and exhaust flow.

LeslieTroyer · Jul 14, 2017

The tstat housing is the best place to measure the temp until it's the worst. Air can leave the housing dry which leaves it colder than normal. In addition to the Tstat housing choose a second or third place ( lower on the engine)and get a feel for how much hotter/colder it is compared to the main target. Then if you get an air pocket you'll know. If the IR has a laser pointer put a target dot where you take the reading. And always be a consistent distance from the target

Les

jssailem · Jul 14, 2017

I use an IR thermostat. I have 6 places that I shoot the engine and exhaust. There is quite a variance from the heat exchanger to a spot by the injectors to the thermostat housing to the exhaust manifold. I record the results against the engine temp gauge. Since cleaning the coolant system and replacing the circulating pump There is less than 5 degrees change from observation to observation. This way I can isolate a problem should it start to occur such as the engine temp gauge show higher than normal. Which of the engine sights is higher then normal.

seadaddler · Jul 15, 2017

I added a temp sensor right before the thermostat on my 3YM and for the last few years the temp reading is at 180 and lately if I raise the rpm's to higher like 2800 it does go to 190 but most times I keep the rpm's at 2400 to 2600 depending on needed speed.
Also depends on water temp here in Fl. And when really cool 180 but when motoring in hot weather for long period and in hurry the temp hit's 190 but never higher.

jssailem · Aug 13, 2017

On my Perkins those would be normal temps. I usually shoot the Injector as well I get temps in the range of 80-86 C . Not all cylinders are the same temp.

kloudie1 · Aug 14, 2017

Ken, attached is the cooling water flow schematic for the GMF.. Your temperatures look OK; Note that the coolest water in the fresh circuit (from the heatex) goes through the FW pump then into the lower block. It goes up where it picks up heat and exits the cylinder head at its highest temperature. The thermostat controls that water temp by either recirculating some back through the pump/block or shunting it into the heatex. Your thermostat should start opening at 71C; that is the water temperature inside the housing, as it is leaving to go to the heatex.. I think you are measuring spots of lowest temp on the engine.. "engine body" is where the "cool" water from heatex enters block.. "pump" is cool water entering the pump from the heatex... Exhaust elbow is cooled by cold sea water exiting heatex and "cool" fresh water in heatex reservoir... "injector" is cooled by diesel and it is insulated from the cylinder head by an internal washer; it would never get to cylinder head temperature, which should be around 75C internally.. Couple that with the inaccuracy of the IR gun, and I think your temps are OK..

PGIJon · Aug 14, 2017

Just an FYI.... Suddenly after returning to the dock a couple of months ago and leaving the engine idle for about 10 minutes or so to let it cool down, the engine buzzer started blaring.... I check everything that I could think of.... finally in the middle of the night I dreamt about a loose Ferris wheel. The next morning, I tightened up the impeller belt and finally the engine ran cooler and has so far (knock on teak) has been running well since. So, if you can't figure out why the engine is running hot, check to see if the belt could be tightened. -Jon

Tally Ho · Sep 24, 2017

I have a 2GM20F and don't have any issues with her overheating, but today I ran her for several hours at around 2800 RPMs. Lake was flat and AP was engaged, so I stepped out on the swim platform where I can reach my exhaust outlet.

I felt the exhaust water (carefully at first thinking it would very hot). I was surprised that if felt almost the same temperature as the lake. Then I stuck a foot in the lake, and then immediately into the exhaust water...and it difinitely warmer, but I would say only 10 or 20 degrees or so.

I checked the engine real quick with an IR thermometer. Was also surprised that the mixing elbow was cool enough to touch, well under 100degrees F.

I just read that the best place to check (or not) is the T-stat housing. I did not check there unfortunately.

Does this sound right, or indicative of a problem? Maybe stuck closed thermostat?

I have plenty of water flowing out the exhaust.

Greg

On edit - if anything, I think my engine runs hot. On the O322, it is in a very tight small "box", and radiates heat for a long time after shutting down.

LakeOntario270 · Sep 24, 2017

Side question: If your thermostat, impellor, and exhaust elbow are setting the engine temperature, why do people say you have to run at 2/3 to 3/4 throttle to get the engine to temperature?

Bill Roosa · Sep 24, 2017

This sounds correct to me. The amount of water coming through the exhaust is more than enough to keep the elbow cool. I know my elbow does not get hot even after long periods of motoring. never actually tested the exhaust temp but if the elbow is cool then I'd suspect the water coming out would be also.

Tally Ho · Sep 24, 2017

Bill Roosa said:
This sounds correct to me. The amount of water coming through the exhaust is more than enough to keep the elbow cool. I know my elbow does not get hot even after long periods of motoring. never actually tested the exhaust temp but if the elbow is cool then I'd suspect the water coming out would be also.

Thanks Bill.

I assume my HX is working, but wonder if the T-stat is working. If it doesn't open, I assume the engine will run hot. But my temp alarm doesn't go off (it has before I fixed an antifreeze leak, so I know it works - or has worked).

Greg

WayneH · Sep 25, 2017

Tally Ho said:
I have a 2GM20F and don't have any issues with her overheating, but today I ran her for several hours at around 2800 RPMs.
On edit - if anything, I think my engine runs hot. On the O322, it is in a very tight small "box", and radiates heat for a long time after shutting down.

Greg,
A bit of background first. A gasoline engine runs a compression ratio of about 10:1 while a diesel engine runs about 18:1 to get the air hot enough to ignite the diesel fuel. To withstand this higher pressure and for durability, the diesel engine is much beefier metalwise. Once you get this mass hot, it does take a while to cool off. You can slightly speed up this process by idling the engine several minutes before shutting it down. But it still takes a while to cool it off. When we are cruising, we would run the engine blower for about 30 minutes after anchoring to help cool off the engine. And we would leave the aft cockpit hatch open for another hour or so to vent the heat.

What's normal temperature what's not

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