I am replacing the thermostat housing on my boat :
During teardown I noticed the thermostats showing quite a bit of corrosion, so I am going to replace them !
It is a A140 degree thermostat.
When I repowered a while back I tossed in a couple of 502 Gen VI motors
I used the old thermostats that were in my old 454 , 1989 big blocks.
Boat ran well did not seem to have any issues plenty of water coming out of the exhaust , temperatures ran around 145 degrees .

I have to replace the thermostats due to corrosion, so while everything is apart the job is simple !

Here is the question the gen VI 502 spec out a hotter thermostat 8M0091470 (160 AF)

I was running A140 degree thermostats and my temps were around 145 should I toss in what I had originally ( 140 degree ) or should I toss in the hotter thermostats that are specified for the 502 at ( 160 degrees )?
Thank You in advance for the reply !
Big Boys Toys

Carbureted 140F.

Most EFI spec 160's. If you use under that, the ECU may still stay in the ending part of it's warm up programming tables.

The motors are of the old school design naturally aspirated , Impco, exhaust manifolds, with stainless steel elbows !
I have no ECU, the motors are 502 Cu In with a pair of 850 CFM Dual Feed Holley Carburetors!
Thanks for replying !

All Mercruiser 1997 and up INCLUDING CARB apps used a 160 degree t-stat and some closed cooled engines use a 170 degree t-stst

even in 1996 the 4.3 carb engine used a 160 degree t stat

all EFI and MPI stock OEM engines used 160 degree t stat

Mercruiser is not the only one do this either

some of this was to help with emissions for having a hotter t stat installed from the marine engine manu's. .

Again to be clear 1997 most marine engines went to a 160 degree t stat. One or two Merc racing engines still used a 140 degree t stat past 1997

All carb apps 1996 and back used a 140 degree t stat. Just saying

I have been running a 160 for the past 15 years, carbed motor.

I run 140's because it is easier to get them to open on the hose on the lift to get a good flush......

I'm old school boat. Carbs, no electronics

Maybe the compromise is a 150 degree ????
I do like the fact that the 140 degree opens quicker , while flushing the motor on a garden hose.
Thank you all for the input !

Yeah, I'm salt water so it was important to me..... Often times we anchor out about 200 yards from my hou and then just idle home so there is no time to Build heat

Mercruiser had this SB out since 1999 and the real way to flush your app. Mercruiser SB posted below for flushing engines and drive water passages running on the water hose.

T stats temp ratings does not make any difference for flushing maybe a 2 to 4 minute difference for the start of opening.

T stats open up gradually anyways not from the fully closed position to the fully open position.

Use what the OEM recommends unless you have a modified set up that requires something different that what the OEM engineered it for.

I bet this SB below is news to most everyone. especially chopping the throttles

http://www.boatfix.com/merc/bullet/99/99_09.PDF

Hey Bup thank you for the service bulletin, just when you think you have it together something new show up.
Have a great day !
Big Boys Toys