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?

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

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.

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.

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.

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.

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

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.