overheats at high RPMs underload

[sebas54]

Hi, I have 1988 gm 4.3l merc i/o on 22 aquasport.

I have been noticing that the engine will run at a high temp anything over 3300 rpms 160-170 degrees. Anything under 3300 rpm it will stay around 140. I have just replaced the t-stat with a 140 degree one.

How much can the temp fluctuate without there being a problem? I never let it get over 170 degrees.

I have changed the impeller, risers exhaust manifolds, and water pump. What could cause this? I don't think that it is restrictions because of all the new parts. Also what are the flappers supposed to do? I saw one of the flappers and it was missing one of its sides.

Another question not related to my overheating problem. Where can I find a intake for my engine. I can't find one and the merc dealer has one for $900. Di don't want to pay that much. The #'s stamped are GM 6269732

Thanks

 

[Don S]

Re: overheats at high RPMs underload

160 to 170? is normal for a 140? thermostat in an engine when under a load.

Situation, NORMAL

 

[sebas54]

Re: overheats at high RPMs underload

Thank you,

At what temp. should I be concerned.

If there are alot of people or a heavy load on the boat will the engine get hotter??

The engine usually stays at 160 but yesterday it was climbing a little hotter.

 

[Don S]

Re: overheats at high RPMs underload

With your normal load, what is your WOT rpm? If you are over propped and not getting your full WOT rpm's, it will cause it to overheat because the engine is overloaded.

 

[sebas54]

Re: overheats at high RPMs underload

WOT rpms are usaully at 4400 - 4500 rpms. I never run it at WOT.

 

[Don S]

Re: overheats at high RPMs underload

It's really hard to say what is wrong with it. Could be as simple as wrong gaskets between the risers and the manifolds. Could also be problems with the thermostat housing check balls (If you have that housing).

 

[xltier]

Re: overheats at high RPMs underload

Hi, I have 1988 gm 4.3l merc i/o on 22 aquasport.

I have been noticing that the engine will run at a high temp anything over 3300 rpms 160-170 degrees. Anything under 3300 rpm it will stay around 140. I have just replaced the t-stat with a 140 degree one.

How much can the temp fluctuate without there being a problem? I never let it get over 170 degrees.

I have changed the impeller, risers exhaust manifolds, and water pump. What could cause this? I don't think that it is restrictions because of all the new parts. Also what are the flappers supposed to do? I saw one of the flappers and it was missing one of its sides.

Another question not related to my overheating problem. Where can I find a intake for my engine. I can't find one and the merc dealer has one for $900. Di don't want to pay that much. The #'s stamped are GM 6269732

Thanks

michigan motors on ebay has them for 189.00 i think.

 

[sebas54]

Re: overheats at high RPMs underload

unfortunately that intake is 1996 and newer engines with 8 bolt patterns. I need a 12 bolt

 

[Bondo]

Re: overheats at high RPMs underload

I don't think that it is restrictions because of all the new parts. Also what are the flappers supposed to do? I saw one of the flappers and it was missing one of its sides.

Ayuh,....

The Flappers are supposed to be there to Stop any Back-Splash of water from entering the motor....
The fact that your's are Burnt Up could be apart of your Problems.... Because when they Fail,+ fall down into the exhaust tubes, they cause massive Restriction...
Unfortunately, My photo hosting site is Down, or I'd show you a picture of what the Problem could be...

 

[sebas54]

Re: overheats at high RPMs underload

Thank you.

I will be replacing the flappers and the check balls.

Is there anyway to check if I have exhaust blockage from the flappers?

thanks again!!!

 

[Bondo]

Re: overheats at high RPMs underload

Ayuh,....

Pull the outdrive,+ Look,...