Hot engine!

[WarriorM]

Overheating problems. We have a persistent overheating problem with our Mercedes OM636, cooled via a Bowman heat exchanger. Assumed have blockage and have taken each part of the system apart – all clear, have flushed water through each part of system separately, also have renewed impeller, checked thermostat,etc.

Symptoms still persist! These are: no problems starting or running, until run at over approx. 1700-1800rpm for more than 10/15 minutes. Quite happy at lower revs for long periods. Appears that there is some salt water (very little) getting into the freshwater system, but nowhere that we can find. Anyone had anything similar and what cured it for you?


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[HenryB]

Had very similar symptoms with my OM636. I tried everything without success until I discovered a small pipe that runs from near the top of the engine water pump back to the block. I found that this was blocked and easily cleared using a small twistdrill (turned by hand). The pipe is there to clear any air in the system which otherwise eventually finds itself trapped in the water pump, making it run dry.

Hope this helps,

Henry


<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by HenryB on 06/09/2003 23:03 (server time).</FONT></P>

 

[Heckler]

sea water in freshwater, usually intercooler leaking
stu

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[kireonriley]

is it a jabsco water pump, if so and it has had a lot of use then try replaceing the cam at the top of and inside the pump housing. a similar problem ocured to some friens of mine .it would apear that at higher speeds the cam does not lift the impelor enough.

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[LeytonC]

Bowmans

When you took the system apart did you replace the seals in the bowman? this
could the cause of the salt water entering the system, i have a similar thing, but i had coolent leaking out.

When you had the tube stack out did you see any scale on the tubes either in the tubes (saltwater side) or the coolant side, this will really reduce the efficency of the heat exchanger.

If everything did look ok, then it could be scale in the engine its self, try removing a core plug and checking. If there is a lot of scale in the system then try running washing soda in the engine for a couple of weeks then drain and flush, this will disolve scale but is kinder than caustic soda. (might be worth doing this away)

This all assumes plenty of water is going thru the system. 1 of the posts said about replacing the cam in the jabsco pump, i would replce all the wear plates as well as the cam and do the seals while it is off.

Also have you checked the temp gauge? everything could be ok and that is reading wrong?

Hope this helps

<hr width=100% size=1>Thanks

Leyton
(EXTAR Solutions - Software that works for you)

 

[david_bagshaw]

I would be careful before using caustic soda, as the heat exchanger body is aluminium, and although we had om314s which had cast iorn heads, arnt the cyl heads on the 636 alloy as well?(caustic + aluminium= gas+ slodge that was a useful part)

Salt water into the cooling water has to be poor seals at the ends of the heatexchanger, (commonly the tapered seat corodes),or failure of the core tube stack

Bunged sea water injection point is another one to look at.

<hr width=100% size=1>David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[brianhumber]

Your description would point to a scaled up and leaking heat exchanger tube bundle. I would check this out-simple enough to do.
Also how are you measuring 'hotness', as gauges can be misleading over time. (my 16yr old temp gauge indicates a running temp of 140C before the 80C stat starts opening at a tested 80C)

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[LeytonC]

If you read my reply, i meant use WASHING SODA, not caustic soda (i had hoped i had made that clear) I had a triumph dolomite which had an aluminium head and i flushed with washing soda with no ill effects at all.

That does not mean i will provide warrenty!!!! LOL

all IMHO of course!

<hr width=100% size=1>Thanks

Leyton
(EXTAR Solutions - Software that works for you)

 

[WarriorM]

Many thanks to all my readers! Several very useful ideas - can't wait to try these- believe the venting pipe suggested by Henry is particularly relevant as we had not found this and have heard of this from elsewhere as well.
Otherwise, yes we have replaced the rubber connectors to the ends of the Bowman unit (are there also separate seals, or is this just the double Jubilee clip on the connectors?), no evidence of any deposits in the cooler stack, but will try flushing - with washing soda solution, but still have a nasty feeling we may be looking for a new unit here as we do suspect the leak is most likely here.
Our measurement of hotness is by keeping a careful eye on temperature variation and by watching the engine when we suspect the problem - we get very jumpy if motoring! We also plan to renew the pressure cap (just to ensure this is OK- tho' no reason for believing it's not). Our problem is now that we can't get out to our boat for a while as she is in the Western Caribbean - so we need to work out a plan of campaign for this sort of problem and go out all prepared. Adds an interesting dimension to sorting elderly boat maintenence problems! Again, many thanks for your advice - any further thoughts most welcome. Cheers, Mike

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[LeytonC]

I forgot to say, i use about 0.5kg of washing soda for an engine,
Hope you get it sorted!!

<hr width=100% size=1>Thanks

Leyton
(EXTAR Solutions - Software that works for you)

 

[idoltyme]

if it is the same as mine it will have 2 inlet and 2 out lets ask a local garage to set up a preasure test on one of the 2 chambers to determine if you have a leak into the other if you need it explaining clearer please mail back only too glad to help

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