E28+ diesel runs hot

[Rob H]

My '83 E28+ inboard diesel engine (original, but apparently serviced extensively a few years ago) started running very hot toward the end of the summer... getting up to 220 after only 10-20 minutes with little throttle... added antifreeze and it helped tremendously... the motor would run at 180-190 for a while at medium throttle, but then after a few hours would still get up to about 210...

Clearly there was some kind of leak or evaporation of the antifreeze over the course of the season... but still, the motor started running a little hot even on the day we added more antifreeze (but thankfully, not nearly as bad as it had been). I'd feel better if the motor could run all day at 180-190.

Any thoughts on how bad or unusual the problem is, what the problem may be, and what to do??

 

[mherrcat]

What model engine is that? M-18? After installing a new thermostat and new temp sender my temp gauge reads just under 160, which I think is low. I put the old temp sender back in and it still reads just under 160. I'm wondering if the new thermostat is not the correct temp.

Seems like in your case you would want to check the raw water pump impeller and the thermostat.

 

[bayhoss]

I have the same engine. First, check the stern exhaust opening to see that you have a good supply of water coming out. Then check your impeller to see its condition. One area that will certainly cause high temp. is the heat exchanger - any idea of when the last time it was pulled and cleaned? Also check your thermostat. A good way to do that is to put it in a pot of water, put in a thermometer and see at what temp it opens. Your engine should be operating at temps. closer to 160 than 180.

Good Luck,
Frank
E28+ Valinor

 

[Rob H]

running hot

thanks for the responses... the impeller was replaced last winter and the water flows fine off the stern... i have no idea when the heat exchanger was last pulled and cleaned but i am quite sure not in the past 3-4 years... I asked the yard to take a look at the situation, maybe the heat exchanger is something they should focus on... but is it odd that antifreeze would disappear over the course of a season? one thing i know for sure, as soon as I added the antifreeze, the situation improved dramatically (despite the fact the motor did get hot after a few hours). also, there was no problem at the start of the season... motored all day the first day the boat was launched, no problems. only in august did this develop.

 

[bayhoss]

diesel runs hot

One thing that is for certain is that the antifreeze should not be going anywhere. It sounds to me like the engine is starting to run hot and then boiling the antifreeze out, which makes the engine run even hotter. Then when additional antifreeze is added it temporarily cools the engine. Then the engine begins to reheat the antifreeze and the overheating cycle repeats. My bet is that its either the thermostat failing to full open or a restricted heat exchanger. Either can show malfunction at any time. The heat exchanger will show gradual increases in operating temp. as its restriction increases, whereas the thermostat will be more inclined to malfunction all at once.
Best Regards,
Frank
E28+ Valinor

 

[Rob H]

thanks again bayhoss

bayhoss-- Your theory makes perfect sense--the antifreeze must be boiling out... I will look into both the thermostat and the heat exchanger. Given the gradual nature of the problem, I have a feeling it's the heat exchanger... you fixed my last problem with the anchor locker getting clogged, so I have high hopes you hit the nail on the head again. Rob

 

[HughHarv]

Small leaks will also cause you anti-freeze to leave the cooling system slowly and the temperature to rise. I'd check any hoses for pin holes and also check for any broken hose clamps. If you see any white pasty build up or streaks around a hose or any cooling system component then you probably found a very slow leak. If you have a coolant recovery bottle, check the tube exiting the heat exchanger to see if it leaks under pressure. Good luck.