Thermo replacement

[Boilermaker]

I have a 1978 Johnson 115, that sat for abt 22 years. I had it checked and the carbs rebuilt last year>>>Ran well! The mechanic that rebuilt the carbs & tuned it DID NOT change the thermostats, and I don't think they ever have been changed (The gaskets still have the factory paint on them).The engine has mostly been used in salt water.<br />Should I try and change them myself??>>>I am pretty good with a wrench & have done a few auto engine rebuilds, but I'm worried abt the cover bolts being in the aluminum engine block for so long. <br />Is this a job that would be better off left to a pro???<br />Thanks

 

[OBJ]

Re: Thermo replacement

Yeah Man!!! Those bolts can be a pain in tha' patut sometimes. Soak them down real good with PB Blaster and see if they will break lose. If they do, your good to go. If they don't, wellllll, could be a problem. Being in the area they are in don't help much I know. You can help yourself out by removing the lower pan bolts and letting it sag down. This will afford you some room to work in. Could be a mean job but if it saves the engine form overheat distruction, it'll be a job worth while doing.<br /><br />Don' hesitate to post any questions you might have. Good Luck!

 

[Boilermaker]

Re: Thermo replacement

It was my understanding that the bypass valves would open and prevent overheating problems if the Thermostats failed>>>But I guess the bypass valves could fail also being they are in the same housing and are just as old.

 

[Dick S]

Re: Thermo replacement

All so let the motor run on hose or tank till it <br />warms up good. may help.

 

[DHPMARINE]

Re: Thermo replacement

Boilermaker,the bypass valves won't open because of thermostat failure.They are spring loaded,and open at higher RPM's,when the waterpump output is high.<br /> If the therms haven't been serviced in all these years,they are hopefully stuck open.Maybe you can continue to ignore them,and you won't have a problem.<br /> If you do overheat,and a new water pump doesn't help,you'll have to address the problem.<br />DHP

 

[Solittle]

Re: Thermo replacement

No ifs ands or buts - you gotta bite the bullet and go for not only the t-stats but the bypass valves, water pump and deflectors in the powerhead. Rebuilds ain't cheap - $2-4K.<br /><br />I did mine (1987 110 hp bubblebacks)last year and am not a professional wrench. Before you start get the OMC factory shop and parts manual specific for your motor. I used a good 7/16" box wrench and a 1/4" drive socket with universal and extra long extension to get the three cover bolts off. I also used rubber bands to hold the assembly together when reinstalling until I got the cover bolts started.<br /><br />Follow OBJs advice on dropping the pan and take your time. Use the search at the top of the page and read up on it before you start. Much has been written on this for these V4s.<br /><br />P.S. I had a professional wrench quote me $200 labor per motor (I have twins) plus parts fot just the t-stats. He wanted to pull the powerheads.