4.3 GM OMC 1988 Sunbird Corsair Thermostat?

[Donald Terrell]

Trying to inspect my thermostat I removed the two bolts holding down the housing to find the spring side sticking down, the spring was hanging off only being held down by one keeper arm.I cant see how I can change the unit,seems to be self contained?Is it just frozen in place by rust?Do I have to purchase from marine shop or can I get it at an auto parts place to save money? I recently changed the impeller, it was completely missing two blades, the oil and lower unit fluid. when I took it out it was missing especially at full throtle only for secs running good like it always has,I noticed that the temp. guage was not rising I thought it was broke,but it wasn't when i muff tested at home,so i figured it wasn't obtaining running temp.Wires,plugs,cap,button all seeemed fine.Would apreciate any advice,sorry for such a long winded request. 1988 Sunbird Corsair 4.3v6GM OMC Cobra

 

[tommays]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

you should only use the marine thermostat ment for your motor a stanard one will fail very fast.<br /> the stat sits in a small rescess were you found it is rusted in place some gental help with a screw driver should pop it out but be careful you dont want to damage what every sealing areas are still left.<br />if you clean every thing up after you get it out there should be a round area that will hold the new thermostat new gasget and you should be good to go.<br /><br />tommays

 

[metwrench]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

Might be an o'Ring on the Bottom holding it in. Look Closely

 

[Donald Terrell]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

Thanks for the help.I will buy the correct stat and there does appear to be an o ring holding it in place but when I scratch on it,seems like metal? I am still confused on how it works and what keeps it in place.It can only keep in or allow water to exit through the exhaust. My theory is that when it gets hot enough to open and sends water out the exhaust this allows fresh cool water to enter the engine and cool it back down.If it were stuck closed(overheat) stuck open as mine(underheat).The diagrams in my service book are a bit confusing.Can water leave the engine any other way than through the exhaust? It is unlike any automotive stat in that it does not sit on the intake after removing the cover rather it is in the top section of the cover controlling water leaving out the exhaust,water can always circulate through the engine.Does the gasket go on before the stat or after and what holds them in place?Water pressure? Is my theory correct concerning operation? THANKS for the help!

 

[elpaso]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

While you have hoses off - flush out engine and manifolds.<br />Those two missing impeller blades went some where - under thermostat ? Stuck in risers ?<br /><br />If you have an oil cooler - blades are probably there, that is the first place that sea water goes.

 

[Lou C]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

The OMC theromostat is held in by a rubber ring that fits into a recess in the thermo housing. You need to use a sharp scredriver to pry out the ring. Go to a Johnson/Evinrude dealer, most can order OMC sterndrive parts. If the passages in the thermo housing are getting smaller because of rust, or there is a lot of flaking rust, I'd get a new housing it is about $60 or so. In the last year I replaced the thermo, housing and manifolds on my 4.3 (raw water cooled salt water boat) and it runs right at 160 like it should.<br />There is a bypass in the thermo housing, so when the engine is cold, it allows water to bypass the thermo and flow out the exhaust manifolds. The water in the block will stay in it until the thermo opens and then it will flow out as well. So if the thermo sticks closed the motor will overheat but the exhaust will still be cooled.<br />While you are at it, see if you can order an OMC shop manual they are very good and not much more than the aftermarket ones.

 

[Donald Terrell]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

THANKS Lou C. I understand now. I can see the bypass where water goes out the exhaust even when thermo is closed and after probing with sharp screwdriver found the rubber ring which I first thought was metal.I have a shop manual by Cylmer. Elpaso was refering to the two missing impeller blades,I think they were blown out a busted power stering fluid cooler caused by improper winterizing.OOPs! Is this what he is refering to as an oil cooler?What parts are called risers,the 2 large things on each side I would consider the exhaust manifolds?Also when I removed the thermo housing a small piece of metal, one of two, holding the spring down was missing allowing the spring to hang half off.Where would this have gone?Should I be worried? The thermo housing is in pretty good shape.Never been in salt water.

 

[Lou C]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

This may have wound up in the intake manifold, but it is hard to guess for sure. If you are not overheating I would not worry about it. On your OMC engine, they used a one piece manifold/riser assembly, the riser is the uppermost part of it. I have heard that debris such as impeller blades can wind up in the power steering (oil) cooler on the rear of the engine. Next time you winterize, make sure you either remove the drain plug in the cooler (hard to get to) or disconnect the hose that comes from the cooler to the thermo housing, and with the trailer jacked down to get the bow of the boat down, point this hose down in the bilge to drain it. I do this with the big hose from the thermo to the water pump on the front of the engine,and the manifold hoses as well. Then drain the block (stick a wire in to make sure it drains) same thing with the manifolds. After it all drains out, I replace the drain plugs in the block and manifolds. Then I fill each hose up with a 50/50 mix of no tox antifreeze and water. Then reconnect the hoses. Of course this is after changing the oil and filter, drive oil, and fogging the motor. I don't like the suck it up the outdrive method of winterizing, too much of a chance of a cracked block if the thermo is not open. I do it this way and no problem even tho it got down to zero here last winter for a while, and the whole month of Jan was below freezing.

 

[Donald Terrell]

Re: 4.3 GM OMC 1988 Sunbird Corsair Thermostat?

Thanks Lou C and every one in this forum. No kidding that the power steering fluid cooler is hard to get to! I had mine repaired at a local radiator shop and I took half my boat apart to remove it.I am off today with my thermo parts in a bag,my housing, and my boat's numbers to our local marine shop. They usually have what I need. Thanks again everyone! Lou C