Mercruiser Overheating

[spbutler]

I know most of you seem to be running outboards but figure someone may have had a similar problem.


A friend of mine has a 1994 350 Mercruiser 4 barrel seawater cooled motor that overheats (200 degrees)mostly when you get it up on plane around 3000 RPMs although he said it has done it idling at the dock. It's a new aftermarket outdrive last year so the impeller should be good. We pulled each hose off at the thermostat housing and it seems to have sufficient water flow.We test drove it yesterday and as soon as you bring it up to 3000 rpms it heats up to 190 to 200 degrees. If you idle it back down it cools down. One thing we notice is there are two hoses to the exhaust manifold, one on top and one at the bottom. When you take the top house off while the engine is running water comes out of the hose like it should but it is also coming back out of the exhaust riser. it does it on both risers. I was thinking some sort of blockage, possibly the flappers in the exhaust tubes broke loose and when under load it can't exhaust the hot water fast enough. The engine circulating pump isn't dripping but still could be failing.
Sorry for the long post but figured I should submit as much info as may be asked. <hr style="color: rgb(116, 137, 172);" size="1">

[flabum1017]

I'd first check the water pump regardless, but the likely culprit will be either a rusted/plugged up up thermostat housing or rusted/plugged up risers.

[SEA YA]

It's a new aftermarket outdrive last year so the impeller should be good.




<HR style="COLOR: rgb(116,137,172)" SIZE=1>

You say aftermarket outdrive, by chance are you running a Sterndrive Engineering aftermarket outdrive? One of their known issues with the Alpha One lower replacements are the water pump impellers. They've had failures where the impeller slips on it's bushing causing reduced water pressure at RPM's above idle which in turn causes overheating. Check and/or replace the impeller. Should do it once a year anyway.

[spbutler]

Yes it is a Sterndrive Engineering Outdrive, we'll look in that direction thanks.
We'll also look at the Thermostat housing, someone else said they had that issue.
If anyone else has any advice or similar problem please respond.

[87allison]

I had same problem on a 454. Mine has a 2nd water pump under right side of engine, kinda hard to get to. On right side if you are standing at the back of boat facind forward.

Randy

[flabum1017]

I had same problem on a 454. Mine has a 2nd water pump under right side of engine, kinda hard to get to. On right side if you are standing at the back of boat facind forward.

Randy


You had a Bravo drive....... no pump in the drive.

[flabum1017]

Yes it is a Sterndrive Engineering Outdrive, we'll look in that direction thanks.
We'll also look at the Thermostat housing, someone else said they had that issue.
If anyone else has any advice or similar problem please respond.

It's easy to check the risers too.... there is an elbow to direct the exaust down after the risers. unclamp ans slide the verticle hoses down and unclamp the horizontal hoses and remove the elbows....you can see the condition of the risers that way. Since it's a 1994 boat, if the risers were never replaced, you will need them by now.

[spbutler]

Anyone have a good site to order manifold riser kits from?

[gransport]

Also check for blockage in the oil cooler , mounted along side of the oil pan .
I have seen Impeller pars stuck in the cooler , blocking the flow .
Also have seen junk in the check balls above the t stat .

[flabum1017]

http://www.marineparts.com/osco/osco14.aspx or your local West Marine

[spbutler]

Going through old old posts I see I never posted the conclusion to this.
The problem was in the SEI outdrive. A piece of casting either broke off or was in the housing from the beginning when it was made and was just floating around in there and would end up blocking the fitting where the water hose connects between the outdrive and the transom assembly going up to the motor, reducing water flow. SEI replaced the upper unit.

[donmac]

install a clear hose on the raw water feed to the engine,fire it up ,watch for bubbles in the hose, bubbles indicate cracked head or bad head gasket,or block. if you have a manifold problem it will usually show water on a plug or in the oil.

[john j 80 viking]

I had the same type of overheating symptoms on an Alpha One. It turned out to be a blown out gasket under the water pump base plate.

Go with a water pump kit first.

[spbutler]

Motor hasn't overheated since SEI replaced upper unit. Piece of casting was partially blocking water hose to motor. Air bubbles were observed before unit was replaced. Luckily my friend saw the piece of metal in the unit when they had the drive off trying to figure out what was wrong. This was after 2 water pumps, cooling hoses, thermostats and flushing out manifolds didn't fix it.

[stvhelm]

I had the exact same problem with my alphas and aftermarket water pump. the impeller slips on the brass hub. As soon as you put a load on it the impeller slips on the hub and has just enough time to melt the rubber a little bit before the motor over heats. Now when you stop the engine the water cools the impeller and then it starts working again until you try to take off and the does the same thing over again. when I pulled my drive I was amazed at what i saw. Then I pulled the other drive (twins) and that one was just about ready to slip too. these impellers only had about 15hrs use. junk. only buy mercs with plastic hubs. plastic and rubber make a good bond metal and rubber no good.

[donmac]

I had the exact same problem with my alphas and aftermarket water pump. the impeller slips on the brass hub. As soon as you put a load on it the impeller slips on the hub and has just enough time to melt the rubber a little bit before the motor over heats. Now when you stop the engine the water cools the impeller and then it starts working again until you try to take off and the does the same thing over again. when I pulled my drive I was amazed at what i saw. Then I pulled the other drive (twins) and that one was just about ready to slip too. these impellers only had about 15hrs use. junk. only buy mercs with plastic hubs. plastic and rubber make a good bond metal and rubber no good. I have only seen that happen to older style impellers that were attacked by ethylene glycol antifreeze,the new impellers are different rubber compound.

[stvhelm]

I have only seen that happen to older style impellers that were attacked by ethylene glycol antifreeze,the new impellers are different rubber compound.


this happened summer of 2008 with my alpha generation2 drives that have the 3.0 style pumps. I think Mallory made them. anyway I would believe that cause I use the pink antifreeze to winterize my engines. very possible