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Mercruiser overheating

marky1212

marky1212

Member
"OK guys I got a good one for

"OK guys I got a good one for ya. 1987 Merc. 454 sea water cooled and have replaced the following: 1 head, both ex manifolds and risers, all hoses, thermostat, engine circ. pump, sea water pump,heat guage and sender. All water hoses including one to outdrive are free of any restrictions. My problem is that engine runs at 175 to 180 at all times. But when I am running wide open and then back down to idle it moves toward 210. I have put 2 new 140 thermostats in but no difference. The warmest part of the engine with a infered heat gun is right before water enters thermostat housing were sending unit is. It is the original housing but no obstructions that I can see when I had it apart to clean and install thermostat. Any help would be greatly apreciated"
 
have you tried hooking up a di

have you tried hooking up a different gauge and see what it does? and what is the temp at the highest point with your heat gun
 
Yes i did change the guage and

Yes i did change the guage and it was the same. The heat gun read 165 when the guage was a little closer to 170 but out in water it runs 180
 
did you replace the Sea Water

did you replace the Sea Water pump completely or just the impeller?

Wondering if it's starving for water or did you use a resticter gasket when installing the risers? what type of risers and manifolds did you use? What type of Head Gasket was used?
 
replaced complete sea water pu

replaced complete sea water pump with housing and all seals. GLM manifolds and risers with restricted gaskets. Head gasket was mercruiser OEM
 
Mark

Are you the guy that y

Mark

Are you the guy that your buddy has called me a couple of times over the last year about?

If so you should call and we can talk
 
"NO, but if you have any ideas

"NO, but if you have any ideas on this problem i could use help. I have only been on this forum a couple of months"
 
I only saw the one on the port

I only saw the one on the port side that I changed the head on and it looked like it was stuck in the open position. I didnt check the on on starboard side. Thats somthing to possibly check. The starboard manifold does run about 20 degrees warmer than port side. What is the function of the shutters and what position should they be in? Wouldnt the motor run like crap if one side was stuck shut?
 
Just how old it this therm hou

Just how old it this therm housing? I ask because there is a hidden passage that cannot be cleaned or viewed.
 
"it's supposed to help red

"it's supposed to help reduce/prevent water intrusion when backing the boat into the water or when slowing the boat quickly from water rushing in addition to the sudden pressure drop of the exhaust

Curious though, OMC has removed them from their replacement Y-Pipes and notes that they are basically useless.

the flappers wont typically get stuck shut, they're not spring loaded just from the natural tension of the rubber.

I'm concerned about the restricter gaskets and with BT about the hidden passage."
 
"Bt, that thermostat housing i

"Bt, that thermostat housing is original. I guess with all the money I have spent on this thing so far I might as well replace it even though it seemed unrestricted. Also, the riser gaskets are the ones with both ends restricted with just a small hole, but thats what mercruiser says is supposed to be there. What do you think?"
 
"Mark is this set up a ALPHA 1

"Mark is this set up a ALPHA 1 or a bravo?

If it is a bravo your problem may be at the transom where the two water hoses meet.

The older bravo's have a pinch collar for the water hose and the aluminum housing around it corrodes/oxidizes and causes the hose to colapse.

Ask me how I know!

High temps are 2 thing and two things only

Either lack of water comming in or lack of water getting out. The causes are what are difficult to find.

If you have a alpha drive the maybe you need to look at the water pump assembly in the drive.

If you have a torn gasket, NO rubber ring on top of the pump housing, or maybe the plastic piece above the housing that the copper tube goes into may have issues. Any place for exhaust gas to get into the incomming water stream

Have you removed the hose comming from the transom and installed a clear hose and watched the incomming water? If it is not almost all water and there are a lot of air bubbles then this would be your issue.

Just some more thoughts.

Again I have had a motor blow a head gasket because of a torn gasket at the water pump assembly in the outdrive!!"
 
"Thanks for the suggestions. I

"Thanks for the suggestions. It is an alpha 1 and a couple of days ago I re-checked all those things you mentioned and they were fine. I did not put a clear water hose on due to the dificulty of replacing that hose and connecting it to transome fitting, but the flow is good. I did remove exhaust bellows and ran it without running exhaust through water housing and that did not help."
 
Did you have a bad impeller at

Did you have a bad impeller at one time?
One with some of the impeller pieces missing?

If so small pieces they sometimes fall down into the pick up area where the water comes into the bottom of the outdrive.

On your thermostat housing do you have the two balls on the long bolt where the 2 top hoses connect? if so do the balls spin freely or are they worn. They can be reversed if need be. How does the spring look that is between them on the long bolt?

These are pressure poppet balls and if they are stuck or malfucntion they can create a high temp condition.

Maybe take some pics of the engine and post so we can see the hose routing?
 
Just got the boat several mont

Just got the boat several months ago and it has had this prob since I got it. I do have reciepts for a lower unit installed about a year and a 1/2 ago. I dont know what happend prior to that.I checked all areas of outdrive for old impellor pieces. None at all. I checked the poppet balls and they are in good shape and springs are good. The guy I bought it from put a new marine engine water pump on thats a bi directional pump. I can't see how the straight vains in that pump can push a lot of water. Ever heard of a defective engine pump?
 
mark you'll find bad in th

mark you'll find bad in the best stuff made. ive gotten bad alt starters waterpumps and even ocasionaly a bad plug or two so yes it happens
 
"Hey guys. If everything else

"Hey guys. If everything else has failed, what would it hurt to remove the restrictor gaskets and go with the open ones? They are apparently only there to ensure an even flow of water to the exhaust risers/elbows. Seems strange that one side is 20* hotter than the other. I'd pull that starboard side and see what's going on. If the other parts were needing replacement, there may be enough restriction in that side to compromise the entire system."
 
Check the hose connecting the

Check the hose connecting the seacock to the water pump. It could be partially collapsed and it would be difficult to tell w/o inspecting it from underneath the motor.
 
It is normal for one side to r

It is normal for one side to run warmer than the other; 20 deg. difference is OK.
 
"The BT Doctor mentioned the h

"The BT Doctor mentioned the hidden passeges in the thermostat housing that may be blocked.Thats about the only thing I hav'nt tried yet. I am going to try a little trick he told me about to see if that is the problem.The restrictor gasket will be the next possible try, but those are what mercruiser recommends. I will let you guys know the outcome this weekend. Thanks for every ones input!!"
 
If there isn't a pipe plug

If there isn't a pipe plug in the bottom of the hsg. the Merc. manual tells how to drill and tap it for a plug to inspect the bypass hole inside.
 
"Well, I put a new thermostat

"Well, I put a new thermostat housing on and still running hot. Took off the 2 month old engine water pump and it looks fine. Does anyone think that water flow blockage to a head could cause this? When I put the new head on the port side it looked like a lot of build up on the old head and gasket were water flows from block to head. I did not take starboard head off. As I said earlier, the warmest part of engine with temp gun is were water is coming out of starboard head to intake right were temp sender is and then go's to thermostat. It is still hot in that area with new thermostat and housing."
 
""Does anyone think that w

""Does anyone think that water flow blockage to a head could cause this?...new head on the port side it looked like a lot of build up on the old head and gasket were water flows from block to head...As I said earlier, the warmest part of engine with temp gun is were water is coming out of starboard head to intake right were temp sender is and then go's to thermostat."

Coolant passage blockages cause all kinds of heat problems like yours. Anything is possible."
 
"Well what I did was take the

"Well what I did was take the hose off the water pump (actually therm housing) and then the one at the outdrive that goes through the transom to the water pump and just blew through it to see if there was a possible restriction and it seemed very clear and easy to blow through. When you say seacock, do you mean the fitting at transome? This overheating thing is really getting to me now."
 
"The seacock - the drilled hol

"The seacock - the drilled hole in the hull where the raw water gets drawn into the cooling system from the lake/ocean - is connected to the water pump via the intake hose. When the pump starts up there is a big vacuum buildup on that hose. This hose is very strong and rigid, but if something got stuck in the seacock at some point, the hose can partially collapse. If that happens, you may only notice a restricted water flow at higher rpms when the water draw should be greater."
 
"The older bravo's hav

"The older bravo's have a pinch collar for the water hose and the aluminum housing around it corrodes/oxidizes and causes the hose to colapse."

As Kghost stated above; I seem to remember another boater found the inside of it narrowed w/corrosion. Pull off the hose and get a good look at it or stick your fingers in it.
 
"sea water pump" as yo

"sea water pump" as you stated made me think bravo drive. I assume that you are referring to the impeller. Was it in one peice when replaced? If not then back flush from the T'stat hose connection w/the gimbal hose disconnected. Also lower the OD and see if there is a kink in the water intake hose from the OD to the gimbal.

Did you happen to run the engine w/o water attached? Impeller will be ruined; may need another one. Did the engine overheat? What did the OD water pocket looke like? Impeller hsg. show signs of melting?
 
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