Stock 502 thermostat
 

What is everyone using?
I had someone tell me the Merc Manual says to use 140
however mine has 165 in it.
My gauges have always read 180 when running, since day one.

What would I gain, loose or possible ruin if I changed to 140?

Also, anyone have the part # for a 140? or cross reference #

Last thought, drilling a couple 1/8" holes to allow more water passage?

Re: Stock 502 thermostat
 

MnFastBoat,
It is my understanding that if you run a lower thermostat the ECU will read a cold condition and the engine will run very rich.

Dail

Re: Stock 502 thermostat
 

I have a 1997 502 Mag MPI and just installed a new Mercury thermostat last year and mine runs 170-175. I would like to know where other 502's run.

Re: Stock 502 thermostat
 

Thanks Walgreen that makes me feel better. That makes sense because the friend who mentioned his ran around 140-150 always has a black transom when he pulls it out.

Re: Stock 502 thermostat
 

My 2000 502efi 'blue motors" came with 140 deg. Thats what merc web site shows when I put my engine serial in the parts look up section.

Re: Stock 502 thermostat
 

thanks Guys.
guess I will leave tehm alone and look into the the port risers haveing a partial blockage
I just do not like how the port side, and more the left bank versus the right bank, has more steam then the starboard motor.

Re: Stock 502 thermostat
 

If you have closed cooling there is a higher stat rating than raw water cooled.

Re: Stock 502 thermostat
 

I was having a problem with my 502s running hot (u can search for my thread). I put in 140s and they now run at 179. I am going to check the actual temp with and infared because I'm not convinced the temp senders are the correct resistance. Anyway, Merc says the 500hp (blue) takes a 140 the 502 (black) takes a 160 therm. See if you can borrow and infared.