VP200D (GM305) odd cooling problem

[Las Palmas]

Hello!<br /><br />I have a very odd cooling problem which have been bugging be quite some time now. I am running a Volvo 200D (GM 305) with a Volvo 280 stern drive. Engine is equipped with fresh water cooling system. <br /><br />Problem is that engine heat goes up really bad on low RPM's. Once on operating RPM's 1500-3500 the teperature is fine but when manouvering in a harbour below 900 rpm's the meter points to red after 30 seconds. When the engine is over heating the manifold and elbow are still very cool (which for me indicates problem with fresh water cirkulation, but I've been wrong before).<br /><br />My problems started last year and I have tried everything I can think of incl. changing thermostat, checking all hoses, changing impeller etc. Then in June I changed the Freshwater/circulation pump and that seemed to do the trick. During July I spent 10 days in the boat and after time the problem started to re-occur but not as bad as before. <br /><br />Now I was out last sunday for a cruise and the problem was back. During my two-hour cruise the temperature kept totally fine but when I entered the harbour again and went down to idling speed it went up to red in less than 20 seconds. After having tied up the boat I let the engine run on 2000rpm and after a minute or so temperature was back to normal.<br /><br />Do anyone have an Idea on what can be causing my problems? Any suggestions on what to try next?<br /><br />Thanks so much in advance!

 

[Stanp]

Re: VP200D (GM305) odd cooling problem

Sounds like the heat exchanger could have scaling inside. pull the caps off the heat exhanger and look inside. there is a bunch of copper tubes inside with small holes. clean out the inside as best you can and use a thin rod to clean the holes out. I've used muric acid to clean the things but it's not recommended. The exchangers should be cleaned out every year or two. An old exhchange can't exchange heat when the copper walls become to thin. This seems to be the answer when overheating occurs at low rpm's. Also, your exhaust manifolds and risers could be clogged. A good test for manifolds is you should be able to put your hand on them comfortably without burning yourself. but you did say they are not hot. Lastly, do a compression check on all cylinders. if compression is less than 120 psi, you may have blown head gaskets causing the overheating.

 

[Las Palmas]

Re: VP200D (GM305) odd cooling problem

Hi Stan,<br /><br />Thanks for your reply.<br /><br />Unfortunately i have also tried your suggestions. I have cleand out each and every pipe in the heat exchanger (was clean already). The cylinder heads have been removed, checked for cracks and mounted back with new gaskets. The oil is fine and there is no water exiting the closed cooling system.<br /><br />When the engine is over heating the freshwater leaving the heat exchanger is about body temperature. Also the manifolds and elbows are about body temperature.<br /><br />For me this sounds like a freshwater cirkulation problem. Could there be some blockings in the engine? <br /><br />I've been considering trying one of those checmical cooling cleeners and then removing water pump and flush the engine with a reverse flow using a garden hose at the thermostat house.<br /><br />Any other good ideas? I'm running out of them.<br /><br />Thanks

 

[Stanp]

Re: VP200D (GM305) odd cooling problem

Oh this is not good. we're running out of options. Maybe u might have a high concentration of antifreeze and not enough water on the closed system. it should be 50% water 50% antifreeze. to much antifreeze coats the inside and prevents proper cooling. The cleaning you describe should clear that up. The fresh water pump- when they fail, they fail big time. I don't think thats the problem. How old is the heat exchangers - when the copper pipes are to thin, they can't exchange heat anymore. last, lets try a more accurate heat guage. I've had my guages tell fasle stories before.