4.3L Thermostat Question

[riverratjody]

I have a 1998 4.3L Mercruiser. Recently bought my boat and it appears that the thermostat may be stuck open, or is absent. The temp gauge never gets over about 105 degrees. I did the electrical test on it and it checked good - grounded out and pegged out. I felt the water coming out of the back and it is just a little warm. I do not have an IR gun but did put a thermometer in the stream and it registered about 100 degrees. Am I right in my guess that it is either open or absent. And, I should check it and replace if it is absent? If the previous owner ran it for a few years like this, has any major damage been done that I need to watch for? Thanks.

 

[Bronc Rider]

Re: 4.3L Thermostat Question

I agree, thermo is stuck open or lacking one. Premature wear does occur from running without a thermo. If it runs fine now I wouldn't worry about that. Raw water cooled engines run a thermostat in 140 degree range.

 

[meesh]

Re: 4.3L Thermostat Question

If you find it to be missing, put one in it. You dont want to run long periods without one.

 

[sdoomaha]

Re: 4.3L Thermostat Question

Need to at least check it....it may also be stuck closed...mine was and the guage was reading low. Your temp sending unit is in the thermo housing on the cool side of the thermostat. If your thermostat is stuck shut, your guage will also read cool beacuse no water circualting through the block is ever reaching it. The slight increase reflected on the guage may just be heat being conducted through the thermo housing itself. You may be running hot and not even know it. Check the circulation pattern of the water through the block and thermo housing in the manual and you will see what I mean. Changed my thermo and all is well.

Good Luck.

 

[riverratjody]

Re: 4.3L Thermostat Question

Thank all ya'll for the suggestions. I'm through for the year so when I winterize I'll go ahead and check and/or change the thermostat. I'm also replacing my exhaust shutters as I've had problems with hydrolock and have found the shutters are completely gone. I do appreciate the help. Jody

 

[180shabah]

Re: 4.3L Thermostat Question

Replace the thermostat, then plan on repairing the problem that "caused" the previous owner to remove it. Possibly related to :

I've had problems with hydrolock

Pull you exhaust manifolds for inspection. Is this a salt water boat? If so manifolds only have a life expectancy of about 5 years.