Overheating?

[Popsy]

My sailboat has an inboard 1979 20 QM Yanmar diesel, just recently it has begun to overheat. The volume of raw cooling water being expelled via the exhaust seems to be the same as always. I changed the impellar on the water pump just in case. I have also tried to clean out the water ways by hand - no difference. The next step may be to backflush through with clean water, need advice on this. Unfortunately, I do not have a service manual which shows the waterways through the block, nor can I find the correct operating temperature. I obviousely need to find a manual ASAP. In the meantime any advice on my problem would be appreciated. Thanks from a confused Popsy.

[linnupesa]

Dear cornfused overeating Popsy

Oh, overheating? Are you seeing steam someplace or only a dial creeping into the red? It may be a stuck thermostat, not allowing water into parts of the engine etc. or a bad indicator showing a wrong temperature or perhaps partial blockages of certain water channels inside the engine head. Good that the water is running at least. With very hot temperatures calcium like deposits build up quickly and a dilute acid flush will get rid of them, but I'd get some mfr. advice on that as there may be damage if it's overdone or done incorrectly.

My guess is it most likely is the thermostat. It should be accessible most often near or below a water hose intake. Google this info and also how to check the thermostat in hot water on your stove.

There may be blockage in the heat exchanger, usually looking like a tube-like affair with water (and oil? ) pipe gozinta and gozoutas on it. Inside are tinier pipes immersed in the coolant, but it sounds as if you have already checked those, right? If not, that is the second good place to check and is also a good and easy candidate for an acid flush.

Any recent period where you had a poor water throughput because of a blocked sea strainer might have caused lime and sulhpate (?) deposit to build up very rapidly.

Worst case, a leaky blown head gasket may be blowing hot exhaust into all the wrong places. Is your oil milky and not nice and black? Are you loosing any fresh-water coolant or is it clearly contaminated? Usually it has red or green glycol mixed in. ( I'm simply assuming here your motor has separated cooling systems, duh! )

Good luck, just my 2 cents worth.

Ivo

[redbopeep]

I do figure you've got a heat exchanger, though some old engines (e.g. the Volvo MD 2 series) allow salt water in the engine block itself.

Sometimes the zinc which is intended to protect the heat exchanger can dissolve in such a way that it blocks the cooling tubes in the heat exchanger. Depending on type of heat exchanger, you can take the end caps off and ream it out. Look at the label/placard on the side of the heat exchanger itself to get additional info. Some heat exchangers are "throw away" type which you cannot ream out. If so, replacing them every couple years is the norm. We have such a heat exchanger on the transmission however the one on the engine may be disassembled to be cleaned (rod pushed through the tubes).

Good luck--let us know how it goes.

[Popsy]

Hi Ivo,

Thank you so much for taking the time to respond to my dilema so quickly.
I should have mentioned I have tried changing the thermostat - no difference. Fortunately there is no evidence of water in the oil and no sign of steam. It takes about 15 minutes for the temperature gauge to reach the red before the alarm sounds. Could a faulty temperature gauge be the cause? My next step is to try and gently backflush the waterways. I have one major hic-up in my idylic sounding lifestyle - my boat is moored off Clearwater beach Florida and I live in the UK. I do fly to the USA at least 4 times a year for extended stays of 4-5 weeks. I do have a friend that cranks up the engine once a month, I wonder if the lack of use could contribute to the problem. My next visit to my boat begins July 17th where I hope, armed with advice, to solve the problem. I will keep you informed after my return to Uk late August.
Regards Popsy

[linnupesa]

Hi Popsy

your new info points even more to a bad indicator or thermostat. As you say it already gets too hot or "into the red" after 15 minutes. Not knowing if it's 15 min. after only idling or powering, I'd say idling 15 minutes is a bit too short to be overheating already, especially as the t-stat is not the problem. Or is it perhaps a spare "call it good but not tested" one, so I'd rather make sure and check if the old one opens up correctly in hot water.

BeBopsie made a good point with her zinc anode crumbling up and leaving hard deposits and debris. This may be out of sight or access for cleaning mechanically but could be carrried up to block a channel in the head ONLY while the water is running... which it does under quite a surprising flow and pressure. It's just a surmise but it could happen.

First though I'd check the sensor. It's good to have a spare anyway. It should come out readily and you could do the hot water test. Not sure if you have a bi-metallic or thermocouple or other type, but it is neither very expensive nor hard to troubleshoot.
Oops, sorry! Both "very" and "hard" are 4-letter words, just like the one, dare I say it.. "boat" ?

One other thing, have you actually felt the rubber or metal hose and/or pipes? Diesels love around 165deg F which is not scalding hot to a quickie touch. The ouchie test may show that all is OK actually, just a false alarm. Or it may be an alarm for perhaps low oil pressure or no generator output and it just coincides with a hot reading?

Always check the stoopid and obvious first! What are friends for, even your "crank-her-up-er" friend could do some of this if so inclined.

Ain't it fun, fun, fun????

Ivo

[Coyote]

To rule out a bad thermostat I always remove it completely. I wouldn't run it that way, but that is a good test. If it heats without a thermostat, the thermostat is certainly not the problem.

[redbopeep]

"Could a faulty temperature gauge be the cause? My next step is to try and gently backflush the waterways."

To check temps:

We have one of these non-contact pocket thermometers. Got it at Harbor Freight as a matter of fact. Non-Contact Pocket Thermometer which works great. You can check temperature of hose (which gives you close to water temp) as well as temp of engine head/block/manifold to get idea of actual combustion temperatures.

Good luck.

[Popsy]

May I thank all those that sent advice on my engine overheating problem, if any of you have advice on the female version of overheating my wife would be very pleased. (Only joking.)
I now feel confident enough to tackle this task upon my return to my boat on the 17th July. When I get back to the UK towards the end of August, I will certainly post a progress report. Once again a big thanks to those who took the time. Hopefully from this to this.

[Popsy]

May I thank all the 'old salts' who gave me such good advice on my boats engine overheating problem , I have now returned to the UK a happy chappie . First job was to crank-up the engine with the thermostat removed, after about 15 minutes of idling the alarm sounded. As suggested by Ivo the next step was the 'ouchie' test. I used the boarding ladder to place my hand (and inavertently my foot) under the cooling water discharge. Hot - but not uncomfortably so, I could have quite easily left it there. Next step was the backflush, some old bits of zinc were evident but again not too bad. Zincs relaced and engine back on a little longer to the alarm. Things are now pointing towards the temperature sender, this was replaced - Success.
Once again a big THANK YOU for all the advice.

From a very relived Popsy.