Engine Running Cold

[Duke 7184]

From what I have seen in the forum this must be the day for discussing engine probolems. I my case the engine appears to be running cold. The temp gauge only comes up to about 100. And, for what it is worth, the water from the hot water heater - heated by the engine cooling water - is at best only warm. The engine is a Yanmar 3GMD that uses raw water cooling only (no heat exchanger). I am not much on diesel engs, but I have already installed a new thermostat and gasket. Where do I go from here?
Duke

[rewell6]

You could take the new thermostat out and check it on the stove in a pot (an old one) using a thermometer. A cooking or laser will do. See what temp it opens at.

The only other thing I can think of is something is rusted through letting cold water bypass the thermostat. How old is the engine? How long have you had the boat? What temp did it get up to before?

One more thing. When is the last time the impeller was changed?

[Omatako]

The only thing that can cause an engine to run cold is a thermostat that is stuck open or has been removed. A damaged impeller or in fact just about any other malfunctioning condition, will cause it to run hot, not cold.

So the final findings of this thread will be most interesting because I don't know of any engine employing a system that provides for a thermostat bypass. The thermostat and it's housing are an integral part of the engine and is the place where coolant finally leaves the engine into whatever cooling method is employed. But all coolant leaving the engine leaves it through the themostat housing or that has been my experience anyway.

The water heater (unless it is also electrically powered) is entirely dependant on engine coolant temp and as long as the engine runs cool, so will the heater.

Just an after-thought - what if the take-off for the heater unit is on the engine side of the thermostat and the return is downstream of it? Don't know how but it is possible.

Ta
Andre

[Rockter]

If it's the same as the Volvo MD17 in principle, then stuck thermostat would be one good reason. You might take the old thermostat, knock the centre out of it, and put that back in again. If the temperature does not cool further, then you could be pretty sure that the new thermostat has a problem, but that would be most un-Japanese.

If it makes you feel any better, you are going to have to have prolonged over-colling to hurt anything in there. It's nothing like as bad as overheating.

[travler37]

Plumbed through the hot water heater?
Coil in heater is rusted out and sucking fresh water through it?
Or new stat is bad...
Mark

[Rockter]

Hey Duke. I had a look at the price you pay for spare parts for this engine.

http://www.marinedieseldirect.com/ca...rintoperators=

Don't complain for a moment. The price of your exhaust manifold is about 1/5 of what I would have to pay for the Volvo equivalent for my MD17C, and your starter motor is just about being given away at the price I see there.

I like the sound of that Yanmar already.

I trust it's a good motor?

[Duke 7184]

The boat / motor is 26 years old.. My God Old Boat. The engins starts instantly and runs smoothly. The only issues I have had with the "engine" has been it running cold. I have had the boat for about 18 months. My wife and I spent last summer renovating the boat and are finally able to enjoy some sailing this year.

[rewell6]

It's also possible the temp gauge or sending unit is bad.

Get a laser thermometer and take it with you on your next trip out. Check the temp before and after the thermostat.

An engine running too cool all the time is not good either. It won't damage the engine. It just doesn't get the oil hot enough to steam out the moisture that collects inside the block from condensation.

My stink pot has a bypass built in the thermostat housing. The bypass port is small so water can flow IIRC. When the engine gets warm enough the thermostat can open and let more water flow.

[Omatako]

Rewell
If you're talking about a tiny hole in the baseplate of the thermostat, that is there purely as a bleed hole so that you don't get air locks in your cooling system. It is too small to influence the performance of the system.
Oh and the engineers will tell you (correctly) that an engine that runs cool experiences accelerated wear. That is one reason that automotive cooling systems have radiator caps - pressure in the coolong system allows the engine to run hotter without boiling. Why? Reduced engine wear.
AA

[Rockter]

It does accelerate wear as the motor does not quite make it up to operating temperature and there is more of a condensation load on the oil.
The oil is better run hot enough to boil off condensation water.
I would fix it, but don't let it stop you using the boat until you do fix it.

It's better than overheating.... that really can accelerate wear.