1995 OMC King Cobra - overheating at high RPM only

[fkonieczny18]

I have a 1995 King Cobra 7.4L. Brand new impeller and brand new thermastat. Engine stays at about 150 degrees when at idle or RPMs up to about 3000. Anything above that the temp climbs. As soon as RPMs come back down, the temp decreases. Any ideas?

How do you back flush the system? Which hose would I use? I am possibly thinking there is something partcially clogging a hose.

Thanks,
Frank

 

[dodge1971340]

Re: 1995 OMC King Cobra - overheating at high RPM only

Hi! that happened to my friends boat it was not a 7.4 but what it was the impeller was all chewed up and the rubber from it was clogging the oil coolers at idle it was fine but with the pieces of rubber clogging the holes in the oil coolers at higher rpms it would heat up. when you replaced the impeller was it chewed up?. what you look for is where the water hose comes from the drive hous to the motor there should be oil coolers they look like logs with water in and out and were the oil in and out i think the 7.4 has 2 one for ster and one for oil but not 100% pos . I would start there to check its the easiest. Hope that helps you!! 8)..... Dodge

 

[fkonieczny18]

Re: 1995 OMC King Cobra - overheating at high RPM only

I will def try that this week. Thank you for the help.

Just in case, any other ideas out there for me to check? What about back flushing the cooling system? Does anyone know which water hose to use?

Once again, Thanks.

Frank

 

[dodge1971340]

Re: 1995 OMC King Cobra - overheating at high RPM only

Hi frank!! I not 100% sure but my seloc man dose not give a backflushing prosiger . only flushing. because a lot of factors come into play like posably flushing whater in threw the exaust and getting water into your oil. there are probably ways to do it. when i did it on mine i drained the system properly and took it apart and cleaned each peice and back flushed just the motor block. mybey there is someone that knows . but i would not backflush threw your rizers and manifolds. hope i helped !!d Dodge

 

[natwales]

Re: 1995 OMC King Cobra - overheating at high RPM only

After you rule out the easy things and check your whole cooling system for restrictions I would also add checking for a blown head gasket as I think that is in line with what you are describing. My understanding is that it allows hot combustion gases to leak into the cooling system thus raising the temp. I remember reading that is usually starts to overheat cool around 3000 rpms.

If you are raw water cooled there is a way to install clear hose and look for bubbles, and if you are fresh water cooled there is some sort of litmus test type check you can do to your coolant.

Hopefully your problem is more simple, but I think its worth checking.

 

[fkonieczny18]

Re: 1995 OMC King Cobra - overheating at high RPM only

I am about to show how NON-mechanical I am here, but what would be some of the causes of a blown head gasket?

 

[bruceb58]

Re: 1995 OMC King Cobra - overheating at high RPM only

An overheat could cause a bad head gasket but I don't think that is your problem. You can do a compression test to make sure if you want. Also check your oil to see if there is water in it.

I think you have a water flow problem.

If you use your boat in salt water, you may need to pull your risers to see if there is any blockage there.

 

[fkonieczny18]

Re: 1995 OMC King Cobra - overheating at high RPM only

It has never been in salt water, only fresh Lake Michigan waters. Also, no water in oil. That looks good. I have had a chance to check the water lines to the oil cooler. Been super busy at work. Will check this weekend.

Thanks again.

 

[cobra 3.0]

Re: 1995 OMC King Cobra - overheating at high RPM only

Did you also change the housing for the impeller or just the impeller?

Your temp sending unit and/or temp guage may be off too. I just about did everything on mine(checked the riser, the manifold, checked the oil cooler, changed temp sending unit, changed thermostat) and in the end the temp gauge wasn't working well anymore. It showed hot and it wasn't. I picked up an auto temp gauge at Walmart for about $10.00 and installed it into the temp sending unit hole. It read bang on at 160 degrees and have been using it now for two years and it remains accurate.

 

[fkonieczny18]

Re: 1995 OMC King Cobra - overheating at high RPM only

I did change the housing and also the liner. Sending unit is a good idea. Hopefully it is not the gauge. I don't want to have a non-matching gauge in the dash. I still and hoping for a minor blockage in the lines.

Still no help on backflushing the cooling system. Any help is appreciated.