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OMC overheating

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ChrisOMC

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"Hi,

I have a '76 OMC,

"Hi,

I have a '76 OMC, 250 cubic\in, straight 6 that keeps on overheating. Recently I changed the head gasket and cleaned out the water passage ways. I also relaced the impeller. The impeller housing appears to be a tiny bit corroded in one spot. I was wondering if anyone could help me to fix this overheating problem."
 
"Chris
With an engine of this

"Chris
With an engine of this age, I would replace any and all water and fuel lines. And in doing this you may find a really soft hose that collapses, or a clogged port or several other things. Remember the fuel line must be double walled, not single wall like cars. Use proper marine style water lines as well."
 
"The Capt. makes a good point-

"The Capt. makes a good point--a soft rubber hose before the raw water pump can collapse on itself, blocking water flow. Had that happen to a car I once owned. Drove me nuts until I spotted the hose collapsing one night.

Jeff"
 
"First maybe you should see if

"First maybe you should see if the problem is in the outdrive or the engine. To do this temporarily replace the long black hose from the intermediate housing to the thermostat housing with a clear plastic one the take the boat for a ride. If you see air bubbles or poor water flow through the hose, the problem is in your bottom end. If this is the case start by ensuring the pickup tube from the cavitation plate up is clear and sealed. Next ensure your impeller and impeller housing are in good shape and sealed. Then pull the side caps on the upper gearcase to ensure these passages are clear. Reinstal with new gaskets. Next check the o rings between the upper gearcase pivots and the intermediate housing side plates. Replace if necessary. Also a good idea to put a lite coat of grease on these to save on wear. This should fix your bottom end problem.
If you have a good uninterupted water flow to the engine the problem could be your thermostat."
 
"HI
I have the same problem

"HI
I have the same problem with overheating too. I have a 81 chevy 2.5L with a 400 omc stern. I replaced the lower pump and hoses and cleared the ports the best I could. It stills overheat.So Took the thermostat out and if the water temp is under 70 degress it run great but over 70 degress it heats up. What I did, I pull the heater hose coming in and place it a bucket and started the motor for about a minut and watch the flow then replace the hose then I did the same to the hose comming out of the bock. Both flowed the same in and out. So I think its in the high rise. I was told if there is a restiction in the flow that it will cause it to overheat. You might want to give a try.
italianmale"
 
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