Overheating or Not?

[TopperHarley]

OVERHEATING ??

Hi,

I own a small raw water cooled diesel engine (BUKH DV8) and am (potentially) having a few overheating problems...

The main symptom I have is after running under load, the engine FEELS HOT and SMELLS HOT. Its too hot to touch, and has a smell thats hard to explain, but that i tend to associate with an overheating engine (entirely unscientific i know!).

Troubleshooting so far.....

1) Water flow at the exhaust (and anti-syphon tell tale) seems OK.

2) The temp alarm never sounds (its set at 80C/170F i think).

3) I wired up a temp gauge (from the same probe in the thermostat housing) and it cycles between about 50C/120F and 70C/160F

4) Checked the thermostat, it opens at 70C/160F

5) Checked the impeller - it was OK

6) Checked raw water inlet - no blockages

7) Checked the flow of the water through the pump - good throughput.


Am I dreaming or is it possible to have the engine overheating, but for it not to show on the water temp gauge (in the thermostat housing) ?

What to check next ??


Thanks,
Craig.

[GILow]

I would trust your sense of smell more than the temperature sensor.

Which bit of the engine is too hot to touch? If it is the block or the head, that would worry me, and I would comment that depending on the engine the thermostat housing may not be the best place to check, as there may be air pockets or blocked cooling passages preventing water from getting to part of the engine, while still keeping plenty of water available to the thermostat housing.

Older Australian Ford Falcon engines were notorious for overheating to the point of siezure while the temperature guage read cold, as the pickup for the temperature guauge was in the head, the first place to run out of water when the cooling water level dropped. I understand that this is not the case with your temperature sensor, but you can see how there might be an air pocket somewhere while the sensor is sitting in nice cool water.

For comparison, my Nissan is recirculating cooled with a heat exchanger, the cooling water runs at around 95 degrees C and no part of the engine is too hot to touch at any point, even the exhaust manifold, and though it smells like something the cat dragged in, it is not a hot smell, just a horrid old greasy diesel smell.

Matt

[Anjin San]

Craig,
Am having the same problem, I have a 1976 (rebuilt) Ford Hollman Moody 172D 59hp diesel engine in my sailboat. Currently checking for oil leaks, she is burning a little more than normal, and am going to check/replace the heat exchanger. Check your heat exchanger (normal use approx. 10 years) that could be an issue. Also - check the engine with a heat gun to see if there are any hot spots - that may help. Perhaps someone out there can also shed some light.
Joe

[Amnesia II]

Your temps sound OK to me...my motor runs @ 170F- 180F comfortably.

[TopperHarley]

Thanks Matt,

My gut feeling is that is IS overheating, and for some reason the water in the thermostat housing is staying at a reasonable temp..... so perhaps some kind of internal blockage.... just not quite sure as to the next step.

The engine was factory overhauled only 3 years ago so i would hope that all the water galleries etc were cleaned then..... how long does it usually take for them to block up ??

[GILow]

Sorry, I'm not a lot of help here as my engine is fresh water cooled, so I have a whole lot of other exciting problems to deal with....

From my own experience of old Johnson 8HP outboards, if you did not flush them after use with fresh water they could block up with salt deposits in the head in as little as a year or less, but the passages on those are very small, probably a lot smaller than a well designed diesel inboard.

If there were any smaller hoses feeding cooling water to specific parts of the engine, I would be gently feeling them for apparent blockage, particularly the thinner hoses... I am reluctant to suggest squeezing them too hard as that might crack them... OK, so if it does they are ready to be replaced I anyway...

Someone on CF is bound to come in with good advice from their own experience of your engine. I do remember reading some threads on flushing raw water cooled engines with descaling agents and the pros and cons of this process. Have you seen any of those threads?

FWIW, the more I think about it, the more I think you should take your sense of smell on this one seriously.

[GILow]

Originally Posted by TopperHarley

The engine was factory overhauled only 3 years ago so i would hope that all the water galleries etc were cleaned then..... how long does it usually take for them to block up ??

On this as a separate point... back in the 80's we had a brand new Johnson 4hp which kept overheating. It went back to the dealer at least half a dozen times before the warranty ran out, and they never fixed it. Years later Dad gave it to me to play with, I found that the cooling passages were still filled with swarth, probably from drilling the cooling passages. There was enough cooling flow left so that the engine would run ok up to about 2/3rds throttle without problem, but any more and it would overheat.

So... is it possible you have a similar small blockage, i.e. does the engine cope fine at lower throttle?

From my limited understanding of raw water cooled engines, such a blockage would not be apparent as there would still be plenty of water flowing out the exhaust, but it would not be so apparent that it was not flowing through the engine. (Again, noting that the temperature at the thermostat is apparently correct, so that flow limitation would have to be on some peripheral branch of the cooling.)

[Jim Cate]

May I suggest buying or borrowing an infra-red thermometer gun. They've dropped in price and are commonly available at consumer electronics/home improvement stores... ie Bunnings or Dick Smiths in Oz. Using this instrument you can actually measure the surface temperature of any place that you can see, and without burning your fingers!

FWIW, I can't hold my hand on my diesel when it is running at its normal 82 deg C... those other guys must be pretty tough!

Cheers,

Jim

[GILow]

Originally Posted by Jim Cate

FWIW, I can't hold my hand on my diesel when it is running at its normal 82 deg C... those other guys must be pretty tough!

Oh Jim, you big softie, and I had you pegged as such a tough old sea salt too.

OK, perhaps I should clarify, there's a difference between "not too hot to touch", and holding my hand against the engine for any significant period of time. I am quite sure that would hurt, despite my years of working as a grill chef.

I mean the sort of touch where you are sensing the engine block temperature with your hand. In those cases on ours it is nothing unpleasant, not painful, just a "Oh yeah, that's pretty warm" feel and you pull your hand away.

I am assuming Craig means instant "ouch" type too hot to touch even for a moment, which I think is too hot for any engine, perhaps with the exception of the exhaust manifold, and even then, it is a properly water cooled manifold that would worry me a bit.

As you suggest, a temperature gun would identify hot spots and tell you if you had any blocked cooling passages.

Matt

[courageous cat]

always nice to have and not that expensive

[Jim Cate]

Originally Posted by GILow

Oh Jim, you big softie, and I had you pegged as such a tough old sea salt too.


Matt

Just old, Matt, just old...

Jim

[GILow]

Clearly you need a good dose of South Australian sunshine. Great for what ails you. And the beer is pretty good too!

[Amnesia II]

Originally Posted by courageous cat

always nice to have and not that expensive

The very one I've just bought on ebay for $25! Thanks for the heads up Jim C.

[TopperHarley]

Just bought the same one too ! - You guys should get a commission !

Just to clarify, when it arrives, ill check around the head/block area... what sort of temp should I be seeing ?

[TopperHarley]

ok... So the IR thermometer aarrived in the post today.... Ill be taking it down to the boat in the next few days...

Any specific suggestions as to how to continue with the troubleshooting ?

Expected temps at which locations etc ??