Mercruiser 140 over heating

[38special]

I just got my 140 running after a rebuild and it will over heat if left at idle for too long. If i bring the RPMs up to 1200 it cools back down.

I pulled the lower end off of the out drive last night and the impeller is in pretty bad shape.

My question is, even with the garden hose hooked up to the muffs and water on, is that not enough to keep the engine cool at idle with a bad impeller?

 

[CheapboatKev]

Re: Mercruiser 140 over heating

I dont think you should not run her at all with the bad impeller.
You may risk pieces breaking off the impeller and clogging up your system further downstream..

Changing the impeller is really fairly simple and should take a couple hours max.

 

[Bt Doctur]

Re: Mercruiser 140 over heating

Pull the whole drive and put the hose in the water inlet hole for testing .It should run normal unless there is another issue.

 

[38special]

Re: Mercruiser 140 over heating

Pull the whole drive and put the hose in the water inlet hole for testing .It should run normal unless there is another issue.

So as long as nothing else is plugged up and even with a bad impeller the engine should still run cool at idle with the muffs on and water running?

 

[38special]

Re: Mercruiser 140 over heating

I dont think you should not run her at all with the bad impeller.
You may risk pieces breaking off the impeller and clogging up your system further downstream..

Changing the impeller is really fairly simple and should take a couple hours max.

It won't be run again until i have a new impeller in it. I am going to check all water passages, hose's to make sure they are open. If they are, again my question is, is it normal for the engine to over heat at idle with the muffs on and water running and a bad impeller?

 

[38special]

Re: Mercruiser 140 over heating

With the bottom half of the out drive still off and the top of the impeller pump off i put the muffs on and and water flows freely out of the pump.

I also took the hose loose at the thermostat housing then used the garden hose to put water to the out let tube of the impeller pump and the water flows good so i know there are no obstructions to the block and head.

So one last time, if the impeller is bad and i know it is, might that be the reason even with the muffs on that i have to speed the engine up to 1200 to 1500 RPMs for it to cool normaly?

 

[cedarjunki]

Re: Mercruiser 140 over heating

yes, most deffinatly...
even though the muffs are on with a bad impeller, you cannot push enough water through the small inlet/outlets of the pump.

thats why they said take the lower off and connect the hose directly to the water inlet bypassing the pump.

 

[38special]

Re: Mercruiser 140 over heating

yes, most deffinatly...
even though the muffs are on with a bad impeller, you cannot push enough water through the small inlet/outlets of the pump.

thats why they said take the lower off and connect the hose directly to the water inlet bypassing the pump.

Thanks. Makes sense to me that with damage to the impeller by increasing the speed it would compensate on how much water the engine needs to be able to cool, in this case abot 1200 RPMs. The seal in the top of the impeller cover is even gone and more than likely losing quite a bit of pressure right there.