Overheating at speed
 

I'm chasing an overheating problem in the right engine of my Scarab III. It will idle all day at 150 degrees (140 t-stat) but take it up on plane and it initially cools to almost 130, then gets hot fast. Throttle back to 1500 and it cools back down. I had the impeller replaced but that didn't fix it. I pulled the t-stat out but that didn't fix it.

Here's what I've done/am doing. Before I button it up, is there anything else I should do while it is apart?

Replaced the raw water impeller-one blade missing

Removed & checked the cirulcating pump impeller-no issues

Removed the raw water strainer-putting new cork gaskets in it, found sand in the bottom

Back flushed the raw water intake line-no issues.

Back flushed the loop from the t-stat housing to the raw water pump. This loop conatins the coolers for oil, tranny and power steering-got some sand and impeller parts out.

Back flushed the block using the holes where the raw water pump attaches-got some sand.

Back flushed both exhaust cooling loops-no issues

Replaced the thermostat with a new mercury 140 degree

All suction hoses are new, wire reinfoced.

All the back flushing was done with a garden hose. It that sufficient or do I need somthing with more pressure?

Thanks,

Check other threads on this , dont know the age of the boat but i would check the fitting where the hose comes through the transom assembly, could be bravo fever,with bravo powered boats getting some age on themthis problem is showing its face more and more. this situation is very inconspicuousand not alot of people know about it,check the other repair forum on this site Good Luck I chased the same deal for 2 years

Thanks for the reply.

I did search the site for answers and saw what you are talking about with the Bravo feaver. I have TRS drives and my water pick up is independent of the drive. It's just a stainless vertical tube that goes throught the transom. No blockage and real good flow there.

Sorry did not know you had trs drives

maybe timing?

What kind of exhaust system do you have?? Do you have stock mercruiser exhaust?? Did the engine overheat? If it did, was the thermostat replaced?

If you have stock exhaust, you may need to replace the risers. The risers get rusted out and impede water flow causing the exact problem you are having.

There are many things to check and you need to check them all but fingers point to the risers if nothing else is found.

Open the block drains and and see if you get any mud or sand coming out.Could be a some blockage in the block.

Also check your plugs and see if you are running lean.

Do you have fresh water hook up on your boat?? if so you maybe sucking air thru the hook up somewhere..

I tried like hell to find any block drains and could not. I know what they look like from other boats, just could not find them on this one.

The engine got hot but did not overheat badly. I have big stainless pipes coming off the exhaust manifolds that go back to the thru hulls. No risers like I'm used to seeing.