Engine overheat

[Dkaseler]

Perhaps someone can help me.
I finally completed the install of a Moyer rebuilt A4. Ran nicely today but it over heated. Why?
This is a fresh water cooled engine so I'm looking at two systems.
There is strong flow of water from the exhaust so the raw water side seems ok.
I suspected that perhaps the impeller pump of the fresh water system was not working (I just rebuilt this pump) but the water coming out of the exhaust is warm so heat exchange seems to be happening.
Could be the heat exchanger but if the salt water side is not restricted I think the fresh water side should be OK.
Maybe the temperature gauge or sender is the culprit but I get readings starting at 0 and increasing to about 210 degrees. I think that if the sender or gauge were the problem I would get no reading.
What am I missing? Any suggestions will be greatly appreciated.
Thanks,
Dave.
PS I forgot to mention that the coolant water in the overflow tank did not rise above the "cool" line when the engine temperature reading was high.
DK

[Dave Neptune]

Dave, are you using a t'stat?

Dave Neptune

[Dkaseler]

Yes, there is a thermostat but Moyer has installed an override valve which when closed acts as if the thermostat is fully closed. Overheated both with and without the valve closed.
Dav.K

[JOHN COOKSON]

Are you sure the thermostat is opening and not stuck in the closed position? Subjective evidence suggests coolant is going through the engine since the raw water side is warm.
To check the gauge & wiring disconnect the wire at the sending unit turn the key on and read the gauge. It should peg at zero. Then ground the same wire. The gauge should peg high.
The resistance in the sending unit should decrease as it warms up. The spec for my Teleflex is at 75* 550-750 ohms and 55 ohms at 212*.

TRUE GRIT

[sastanley]

I would remove the t-stat, close the by-pass valve and see what you get. It is the simplest test to start with. Not sure I understand the "override valve" you describe. Maybe you mean the by-pass?

Put the t-stat in a pot of water on the stove with a meat or candy thermometer and see if it opens as prescribed.

How big/type of HX? Since the FWC side of the A4's run at such low pressure, when the engine is cold you should be able to open the radiator cap and see if there is circulation on the antifreeze side at first start up. I have an electric antifreeze pump and water rushes by the HX opening.

[Dkaseler]

Thanks. Yes when I said override valve I'm referring to the bypass. I'm going to run the engine with the cap off the heat exchanger and see if I see flow. If I do, I'll remove the thermustat and see if that helps.
Dave.K

[sastanley]

Good approach Dave..one step at a time..I have a pretty small HX (smaller than the one MMI sells) and I am not having any trouble with cooling (I do run mine without a t-stat...but I've done that since the conversion.)

Be sure to report back!

[Dkaseler]

Thanks Shawn,
I only got as far as removing the cap on the HX and closing the by-pass valve. When I ran the engine I could see no turbulence in the antifreeze under the cap. But in my case there is a "reservoir" on top of the HX which puts the hose with the coolant about 6" below the cap. Not only did the reading on the temp gauge go to about 210 degrees but the HX canister was very hot to the touch. Is that normal? Tomorrow I will drain the antifreeze, remove the thermostat and check the impeller on the pump. Yesterday I reported incorrectly that I had rebuilt the pump. The pump I rebuilt is the raw water pump and that appears to working fine. The antifreeze pump came with the rebuilt engine from Moyer and should be fine.
That's were it stands. Thanks for your input.
Dave.

[sastanley]

Hmmm,...

OK, Dave..maybe we need to find another way to confirm the antifreeze/fresh water pump is working. The HX should be really hot to the touch, but not 210°F.

Again, if it was me, I'd remove the t-stat and see what the results are...210° F is too hot. I was running at 2,250RPM this evening in 81°F river water with an engine temp at 185°F. (No t-stat). When I don't run her so hard, it is usually 165-170°F.

You probably don't need to drain too much..how much higher is the HX than the t-stat housing? You will only lose the antifreeze to the t-stat housing.

Do you have one of those infrared gun style thermometers? I would still trust the boat gauge until we have reason to not trust it.

edit - Also..if you can take any pics of anything we are talking about, they always help..you can upload them directly into your post here on the MMI forum with the "Go Advanced" button, provided you know where to find the pics on your phone..(I am old school, I always upload them to Google photos and then save them to my file server at home and then add them that way )

[Dkaseler]

I really appreciate you helping me think this through. My guess is that if the HX is getting so hot to the touch the coolant water pump must be working to circulate that hot water to the HX. I find it odd that the HX is getting so hot and am starting to think the trouble is in the heat exchanger.
I'll let you know what I find after I remove the thermostat.
Dave.K