4.3L Overheating!! Tried everything I know

[cbr9rr]

I have a recently rebuilt 4.3L Mercruiser with raw water cooling. It overheats at all speeds and rpm's. I shut it down when it gets above 200, but it would go higher. I've checked so many things that I don't know where to look next. I first replaced my thermostat and all related gaskets. Next, I replaced my lower unit impeller, upper and lower housings. Replaced my G.M. water pump on the engine block. And I did check proper flow from the outdrive by using a clear hose from the oil cooler to the t-stat housing, no bubbles at all just pure water. O yeah, I checked inside of the oil cooler and it was very clean. I took off the risers and manifolds to check for blockage, and they appeared to flow well. I stuck a water hose in the inlets and the water flushed through with no problem. If there is a lot of rust, but good water flow, could the rust still inhibit the motor from cooling properly? One side has a new exhaust manifold and one has an old manifold, the older manifold definitely heats up faster than the new, but the water flows through it fine(garden hose). Please help, I've read everything I can and tried everythin I know. Richie

 

[jomac]

Re: 4.3L Overheating!! Tried everything I know

Ummm! sounds like you checked everything good, I'am no I/O mech but if that motor was in a car I'd be looking at timing(may be to high) and carb settings (running to lean) both will cause one to overheat. Good Luck!

 

[Trent]

Re: 4.3L Overheating!! Tried everything I know

You said no bubbles......No bubbles at WOT is what you should have! No bubbles FROM THE OUTDRIVE. The hose comming in from the transom. If you have bubbles their you have a outdrive problem. <br /><br />Yes rust can cause a problem. Check the water from the outdrive first.

 

[karayj]

Re: 4.3L Overheating!! Tried everything I know

typically when the coupler goes your engine will start to over heat because if the driveshaft isn't turning then neither is the water pump impeller down in the drive plus usually the coupler will smell from burning rubber...good luck

 

[karayj]

Re: 4.3L Overheating!! Tried everything I know

have you tried running with out a thermostat just as a test for no more then 15 min??? as i read you post more i realized it cannot be the coupler the thermostat could be bad something may have happened on the install or its defective and you need a new one just becasue it new does not mean it cant be bad think about it a company produce 200,000 thermostats a year you will have a few bad apples slipping through ...

 

[echozulu]

Re: 4.3L Overheating!! Tried everything I know

you aint gonna be happy pappy...combustion leak..aka head gasket...

 

[cbr9rr]

Re: 4.3L Overheating!! Tried everything I know

I have checked my timing, it's actually set a little low(4 deg)because I was suspecting that as a potential culprit. The carb is also adjusted properly, I double checked that also. I've tested it with and without the t-stat, and it still heats up without the t-stat, it just takes a little longer. About the possible leaky head gasket? I've though about that, but would'nt I also have water in the oil? Trent---There were no bubbles at WOT, I brought it out to test that today. The clear hose stays completely full, with zero bubbles. I don't know what to check except for a head gasket. Could'nt I do a compression check on the cyllinders to check this? Thanks for the replies guys.. Richie

 

[Boatist]

Re: 4.3L Overheating!! Tried everything I know

Happypappy<br />Welcome to the board<br />Sounds like you have check about everything. My wild ass gess is manifold. Let me ask some questions and see if it helps.<br />ON muffs when you turn the water on before starting do you get water out of the outdrive?<br />On muffs when you start engine does water coming our the prop warm up slowly then when the thermostat open heat up quickly?<br />Is the engine actually getting hot or could it be a bad sending unit?<br />You tried a clear hose from outdrive but did you just take hose off and see how much flow you have from outdrive? Should be a good steady flow.<br />You ran water thru your manifold I assume thru the water pasages, what hind of pressure did you use? A garden hose at 40 pounds should make water flow but will it flow at 5 pounds of pressure?<br />I do not know year of your motor but are your manifolds feed by a rubber hose from the engine? If they are I would disconnect with the motor hot and off then run over the side instead of going thru the manifold. Sart engine and watch the guage and the flow out of engine. The water should be hot if the engine is hot and thermostat open. If the engine cool right down then you know manifold is blocked. No cooling to manifold this way so only run long enough to see if water coming out is hot and if engine cools.<br />Last thing I can think of and again I do not know your exact engine. You changed the water circulation pump but did you check the pump input hole to make sure not bolcked by a gasket or rust. Most suck cool water in thru a hole that get sea water from the outdrive, Mine is right before the thermostat where the outdrive water comes in. I have seen people change thermostat and use wrong gasket and cover the circulation pump input hole and I have also seen that hole get blocked with rust and scale.<br />Can you put your hand on the top of the thermostat and tell when it opens?<br /><br />Basic flow is out drive impeller pumps water up to engine. Remove hose and make sure have good flow there. Next engine circulation pump suck water out of that water coming from outdrive and pump it into the engine. Circulation pump also circulates water in block and head. Sea water also flows on into and out of both manifolds. When the temperature in engine get to 150 degrees the thermostat should open and since the circulation pump is pumping water into the block hot water will flow out the thermostat and more cold sea water will be pump in by the circulation pump. The hot water flow out thru the manifolds then risers down and out the prop. <br /><br />Please come back and tell us what fixes it.

 

[cbr9rr]

Re: 4.3L Overheating!! Tried everything I know

Boatist, thanks for all of the suggestions. My exact motor is a 1988 4.3L Mercruiser with an Alpha one gen.1 outdrive. I believe that my t-stat is working properly. I did take off the hose that is leading to the exhaust manifold, and yes the water is hot, both sides. Right now my temperature sending unit is located inside of the t-stat housing, what is more accurate there or in the intake manifold? I've pretty much ruled out my impeller/outdrive water supply as the prolem. It's brand new and I checked it for bubbles and after you mentioned to check the amount of flow, I checked that also and that was very good also. I have thru-hull exhaust, so I can check the water temps from both sides of the engine. The portside exhaust is about 10 degrees warmer, but that does not seem to be an issue. I'm going to check compression soon to see if that could be an issue. My engine runs beautiful, with no water in the oil, so I really don't think that is a problem but I'm running out of things to check. Thanks everyone for the input, I'll keep you posted. Richie

 

[Good Sport]

Re: 4.3L Overheating!! Tried everything I know

If that make has an external water pump, make sure that the belt is not slipping. A friend of mine had a similar experience to yours, Pappy, and after a lot of frustration, a simple tightening of the belt fixed it.

 

[SystemF]

Re: 4.3L Overheating!! Tried everything I know

This may seem stupid, but I just wanted to make you double check. Thermostat is not in backwards?

 

[denniz]

Re: 4.3L Overheating!! Tried everything I know

Probably would fit backwards, SYS. Do you think they open at different temps when upsidedown? Thought id ask....

 

[Boatist]

Re: 4.3L Overheating!! Tried everything I know

Rod knocking<br />Yes if in backwards it probably would not open at all. Spring and cylinder would be on side with cold water on it instead of on side with hot water in the head. Also the the hole that allow air to excape so hot water get to the thermostat need to be open.

 

[flashback]

Re: 4.3L Overheating!! Tried everything I know

boatist mentioned the sending unit, is your engine actually running hot or is it just the gauge telling you that? can you touch the engine without getting burned? you should be able to touch it for a few seconds it will feel hot but not hot enough to burn you... 200 degree water exiting the exhaust is not a problem.