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#470 MERCRUISER OVERHEATING

K

kedwards

New member
The engine overheats at higher

The engine overheats at higher rpm's only. I've replaced the OD impeller it checks out fine. I've cleaned out the heat exchanger and tested it and it's OK. The water pump looks good not sure on how to test it. I've checked all of the hoses for blockage and found none. Any ideas of what I should try next? Could I have a blown head gasket? Any suggestions would be appreciated.
 
"[b]"Could I have a blown

""Could I have a blown head gasket? "

Ayuh,...

If you Do,...
The coolant tank will be building Pressure,+ blowing coolant....
Or atleast Bubbling....

A Compression Test will tell you the Answer...."
 
Haven't seen any bubbling

Haven't seen any bubbling or loss of coolant. Any other ideas? I appreciate your compression test suggestion.

Thanks again!
 
I have checked the hose from t

I have checked the hose from the OD Impeller and it runs very strong like a gardon hose on high. Anything I'm missing.

Thanks!
 
Replace/test the temp sender.

Replace/test the temp sender. It may be giving you a false temp reading.
I once played that game when I was new to boat repairs with a 470 for 3 days.

I pulled the old sender out and got a new one.
I boiled some water and with a ohm meter attached I watched each as there resistanced changed.
(~60 -80 ohms to ~240 ohms is the range and it should change slowly)
The old one jumped almost 30-40 percent when it hit a certain temp. The new one climbed slowley and normaly. Replaced the sender and all of a sudden the operating temp was dead on and correct.
 
What do you consider overheati

What do you consider overheating? Just asking because the 470 runs around 160-170 at speed since its a closed cooling system. I too had to replace the temp. sending unit AND the 20 year old gauge before I got an accurate reading. Also my 470 tended to creep up to 190 while on plane. An upgrade to a 4 inch heat exchanger cured that problem.
Chris
 
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