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.

The whole system is raw water. I considered there might be an air leak so I'm replacing the cork seals in the sea strainer and have checked all the clamps for tightness.

That's worth checking. I know how to do timing but have never done it on a boat. What is the procedure and setting?

Thanks,

Steve, How long have you owned this boat? Did it just start happening or was it after a repair?

This is my 3rd season with the boat. The problem just showed up one day. We like to anchor in shallow water with a sandy bottom and I have found some sand in the strainer and lines so I think maybe that is the cause.

The problem is I can't seem to solve the problem. This time I tore it down and flushed even more sand out. Right now, everything runs clear when I backflush. Before I put everthing back on, are there any other tests or procedures I should do?

Right now, given all the sand I got out, I'm cautiously optimistic.

Thanks,

It's extremely rare but sometimes the hose from your intake up to the strainer/water pump can collapse even though it's a wire bound hose. As the hose gets old the inside of the hose seperates from the outside and the more throttle you give it the more the hose collapses....

It's an outside shot but if nothing else just replace the hose to be sure.

Good tip. Thank you.

Did you look through the oil cooler?. I have backflushed and things looked normal but there where impeller parts, sand, lodged into the tubes the water passes though.

They would not come through backflushing them.

Did you find the missing vein from when you replaced the impeller?????

If yes, replace the entire housing for the sea pump if its one of the plastic ones.

ONLY USE MERC IMPELLERS/HOUSINGS!!!!!! The Sierra stuff is junk.

I did not look through it. It is nearly impossible to even reach. I'm not sure I could get it out without either pulling the engine or removing the exhaust manifold.

In your case, how did you get the crud out? Do you think I could back flush with more pressure some how to dislodge any stubborn stuff?:readinghelp:

I found a bunch of impeller parts when I back flushed. I did not try to determine if I had accounted for all the pieces though in hind site, I should have.

I bought a Sierra but after reading some threads here I bought a genuine Mercruiser kit and that is what's going back in.

What are the possible materials my housing would be made of? Mine might be plastic. It is light and does not sound metallic when tapped.

Remove and clean out the oil cooler.

I seen it happen several times. I used a stiff wire and pushed it through and needle nosed pliers on the other stuff. I have even seen small rocks from the sand stuck in there.
You might be surprised when you look through it.

They are either plastic or aluminum.

The plastic ones are one piece with 1 SS plate and the aluminum body ones are 2 pieces with 2 SS plates.

Aluminum one is first on page, plastic is second on page.
http://boatfix.com/bykeywordmerc.asp...kit&texttype=2

Thank you for the clarification. I think I have the aluminum one. A merc dealer said it is no longer available but I'm happy to see boatfix has it.

Here is what mine looks like:

Fixed it!!!
 

Tried again to get to the oil cooler. It's not going to happen unless I pull the exhaust manifold.

I put everything back together and guess what? It does not overheat. Yeah.

The engine is running 10 degrees hotter than the other one, port = 145, sbd = 155, so I'm pretty sure I still have a restriction in the oil cooler.

If I can just get through the rest of the season, I'll pull it all apart this winter.

Thanks everyone for helping.:ernaehrung004:

oil cooler!!
especially if around low water levels and sand :(
I back flushed, removed hoses, new impeller and housings and still the same thing!
even went after the hose in the gimbal/drive connection.
nothing helped!
until i pulled the oil coolers off and found to have only 3 open channels!!!!
took a lot of coat hangers/patience and pushing-pulling and pounding to get them clean.
However it all paid off because now they run cool and I did not have to spend $287/each for replacements :(

Yea, sounds like me. As much as it's going to be a PITA, I think that is what I'll have to do. Since she's not overheating now, I'm going to wait until winter. That way it'll be even more fun since everthing will be nice and cold.

I have had similar problems
Problem was the feed hose to the sea pump was being sucked closed when it higher rpm when more suction was created - collapsing the hose.
The problem caused impeller failure and caused the pieces to be clogged at the cooler-back flushing eliminated the large chunks from the system-however there were some that were clogged at the thermostat-also there were some that "melted" their was thru the system.

Anyway, the hose would not collapse on the garden hose, just under a load when in the water under power. check that system for faults. Possible - trying to help
Good luck