Mercruiser 233 Overheating--Out of Ideas

[johnkom]

"Did you replace the separately purchased water pump base/seal housing and gasket?"

Yes. All new.

Thanks for the great ideas. I need to get some clear hoses.

 

[johnkom]

Got a chance to do a little more trouble shooting today. I had the daughter drive the boat hard on plane while I laid down next to the engine. I was able to verify that the intake hose from the stern to the thermostat housing is NOT collapsing. I then disconnected that hose and ran it into a bucket at idle for a minute and got four gallons of water. Does that flow rate sound about right, 4G/min at idle?

 

[dubs283]

That sounds like enough water supply to me. Seeing as hiw you've got a basically entire new cooling supply and removal system have you checked the outflow of cooling water from the exhaust?

After the risers the y pipe exits the exhaust gases and cooling water. Don't rule out a blockage in the y pipe, exhaust bellows, idle relief ports, or the exhaust passage in the drive

Have you installed a new t Stat and gaskets?

 

[johnkom]

"After the risers the y pipe exits the exhaust gases and cooling water. Don't rule out a blockage in the y pipe, exhaust bellows, idle relief ports, or the exhaust passage in the drive
Have you installed a new t Stat and gaskets?"

Yes. New exhaust flappers and thermostat.

 

[Bt Doctur]

Have you eliminated the PS cooler? If everything else was checked then suspect a leaking head gasket blowing combustion gas into the cooling system

 

[johnkom]

No PS cooler on this boat. I hope to installed some clear hoses this week to see if I'm getting air from the engine.

 

[johnkom]

I think I'm finally on to something. I put clear hoses on the hose from the outdrive and from the thermostat housing to the manifolds. It is definitely sucking air at the outdrive pump and pushing air into system. I remove the boat from the marina next week and will pull the lower unit off. Air has to be entering before the pump. After the pump it is under pressure. The video is at idle.

 

[Bondo]

Ayuh,..... That's in the water, drive down,..??..??

 

[kenny nunez]

What you were seeing was a leaking head gasket. The combustion gas escaping was overcoming the incoming water pressure. A compression test very seldom will show which cylinder is causing the problem unless the gasket is completely blown out. Even after the heads are pulled you probably will not be able to see where the gasket is leaking.
All this started from when the engine overheated in the past.
Pull the heads, have a valve job done and have them re surfaced.

 

[johnkom]

Yes. That's why it's so muddy. River water, in the marina, boat just barely floating. Running churns up the mud.

 

[johnkom]

What you were seeing was a leaking head gasket. The combustion gas escaping was overcoming the incoming water pressure. A compression test very seldom will show which cylinder is causing the problem unless the gasket is completely blown out. Even after the heads are pulled you probably will not be able to see where the gasket is leaking.
All this started from when the engine overheated in the past.
Pull the heads, have a valve job done and have them re surfaced.

Engine never overheated. Air bubbles are in the left hose coming from the outdrive "before" it enters the engine.

 

[johnkom]

EUREKA! Found the problem. Gasket under pump was allowing air from the exhaust chamber to be sucked into the pump. Look at the pictures. The mating surface was irregular and the gasket was not properly made/fitted. The two conditions allowed exhaust gases into the pump. Cleaned and trued up the surface and installed new, better fitting gasket and no more cooling issues.

 

[dubs283]

"Did you replace the separately purchased water pump base/seal housing and gasket?"

Yes. All new.

Recent pics show fairly deteriorated gasket

You removed the newly installed base and gasket to discover this?

 

[johnkom]

Yes. That is the gasket under the water pump base. I had an air leak at that drive shaft seal two seasons ago. So I replaced the entire pump including base and all new gaskets. That is why I was so late to check that area for a cooling problem as I had just been in there. I did not notice the poor fit for the gasket. It was only touching about half of that mating surface. Attached is a picture of the seal air leak blowing bubbles.

 

[Lou C]

What you were seeing was a leaking head gasket. The combustion gas escaping was overcoming the incoming water pressure. A compression test very seldom will show which cylinder is causing the problem unless the gasket is completely blown out. Even after the heads are pulled you probably will not be able to see where the gasket is leaking.
All this started from when the engine overheated in the past.
Pull the heads, have a valve job done and have them re surfaced.

Yep been there done that. Catch it quick before more damage is done. Get a set of Fel Pro marine head gaskets & ARP cyl head bolts & get your heads checked for cracks. If too far gone just buy a reman set; just match up casting numbers.

 

[Lou C]

EUREKA! Found the problem. Gasket under pump was allowing air from the exhaust chamber to be sucked into the pump. Look at the pictures. The mating surface was irregular and the gasket was not properly made/fitted. The two conditions allowed exhaust gases into the pump. Cleaned and trued up the surface and installed new, better fitting gasket and no more cooling issues.

Ahh good catch. This is why the clear hose test is so important.

 

[dubs283]

I had an air leak at that drive shaft seal two seasons ago. So I replaced the entire pump including base and all new gaskets. That is why I was so late to check that area for a cooling problem as I had just been in there.

Two seasons does not equate to recently replaced

Merc recommends full water pump replacement every 2-3 seasons

 

[johnkom]

"Two seasons does not equate to recently replaced

Merc recommends full water pump replacement every 2-3 seasons"

Really!?! Water pump base and gasket replaced January 2021. I had a whopping ten hours on that pump base. It was bad from day one. Had nothing to do with seasonal interval.

JK

 

[Scott06]

"Two seasons does not equate to recently replaced

Merc recommends full water pump replacement every 2-3 seasons"

Really!?! Water pump base and gasket replaced January 2021. I had a whopping ten hours on that pump base. It was bad from day one. Had nothing to do with seasonal interval.

JK

Oem part or aftermarket?

 

[dubs283]

Really!?! Water pump base and gasket replaced January 2021. I had a whopping ten hours on that pump base. It was bad from day one. Had nothing to do with seasonal interval.

Yep, really. 20 months covering two seasons. Doesn't matter how many run hours you have, in fact many believe not using the product causes premature failure.

Looking again at the recent pics it also appears no gasket sealer was used on the base gasket which is oem protocol.

Nothing you have stated or task performed is out of the ordinary. Your experience is a well known issue among mc-1 and alpha/r/mr drives.

Maybe you did receive a faulty gasket/base assy but based on info provided I'd say most likely the issue arose from a lack of gasket sealer upon install and time between replacement and failure, ymmv