Mercruiser HELP!!! overheating ! cooling system gone through !

A 1987 4 cyl merc I/O, very low hours, new exchanger, t-stat, coolant, system flushed, told the fws is a bronze impeller dosent need replacing, I adjusted the fuel mixture, it can run longer but still overheats, new outdrive imp as well. I dont know where to go ! help !! oh the shifting gets difficult when she overheats !

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

doctordelerious said:

told the fws is a bronze impeller dosent need replacing,

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And what exactly is that?



Have you checked / replaced the manifold and riser lately?

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

doctordelerious said:

A 1987 4 cyl merc I/O, very low hours, new exchanger, t-stat, coolant, system flushed, told the fws is a bronze impeller dosent need replacing, I adjusted the fuel mixture, it can run longer but still overheats, new outdrive imp as well. I dont know where to go ! help !! oh the shifting gets difficult when she overheats !

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Are you talking about the impeller or the fresh water pump on the front of the engine as I've never heard of a bronze impeller in the lower unit.

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

Ayuh,... I'm Guessing you have a 470,...
If the impeller is moving water Into the HE,...
Is it able to get Out through the Riser,..??

I'm also Guessing it's Not...
That'll cause the exhaust downpipe to run HOT,+ probably it's melting the lower shift cable, causing the shifting problem...

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

The fresh water system Has a bronze impeller. I last year I removed the riser , exhaust and intake maniflods, all clean, this boat has maybe 90 hours in total, always flushed after salt use.
TODAY I did some more work on it, I ran it @ idle for about 1 hour, I used the ir heat gun, the system has no particular hot spots, on the exhaust port on the head I am reading 245 degrees, directly on the other side of the cooled exhaust manifold it reads more like 210. I did however notice large ammounts of air coming from the oil fill, sometimes she acts like she has timing issues, but I did the timing already. I cant afford to take her to a mechanic, I can barely afford parts, I am a moderately expirenced mechanic but this has got me.

Thanks, Aaron.............. BTW it is a merc 165

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

water in -water out
impeller
water pocket cover
water connecting hose
P/S cooler
heat exchanger
exaust riser
therm stat
Normal temp about 160-180

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

BTW it is a merc 165

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Ayuh,... Like I said, a 470....

If it's not Blowing antifreeze...
You need to look at the Raw Water Cooling side of things...

Re: Mercruiser HELP!!! overheating ! cooling system gone through !

If everything else checks out, do a leakdown test and check the coolant tank for bubbles. 470's (aka 1987 165) are known for blowing the head gasket due to the open deck design. If you get a lot of combustion gases in the cooling system, it will overheat.