Mercruiser 305 V8 running hot at low RPM fine at Speed

[thomascrown]

0A612838 suggest the engine to be an 1986 Stern Drive (200) Model number 02002346... Your engine should be running the 140 degree, https://www.crowleymarine.com/mercr...-drive/1986/-02002346/standard-cooling-system

1986 Stern Drive 200 [02002346] - Parts Lookup | Crowley Marine

View parts diagrams and shop online for 02002346 : 1986 Stern Drive 200. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

Mercruiser Service Manual Number 9 for sale | eBay

Get the best deals for Mercruiser Service Manual Number 9 at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

Much appreciated. Confirmed I do have the 140 thermostat.

 

[dingbat]

River is 48, lake is 40.

Yep..same thing.
Stuck in the overheat, over cool cycle.

Not enough heat to open stat until rev kick up. Stat opens, engine cools, stat closes process starts all over again

Have seen by-pass holes drilled in stats to help with this problem.

 

[Grub54891]

always ran a 140* thermostat. She runs about 120* slow cruising. Get on it and it’ll climb the 140-150*. Not an issue for me. Have a good impeller, no suction air leaks. Lake Superior waters,and small inland lakes with warmer waters.

 

[Scott06]

Ok, well... Looks like it's pretty random what got what. Newer v6/V8 trends towards 160, but many engines come with either. Older were mostly/all 140 that I see. No clear cut crossover if vortec or 4bbl. The fi models I looked at were all 160. So I stand corrected and idk if it matters.

I suspect it has something to do with emissions rating original engine had one of these CARB rating star stickers on it - I want to say the 2 stars. IT was originally a 4.3/190 hp with a Mercarb that had the antitamper cover on idle mix screw. Surely set as lean as possible to pass emissions and not work after 3 years... I would think the higher temp thermostat would help emissions.

I replaced the original engine with a 5.0 w/ Edlebrock 1409 but swapped over thermostat housing etc and kept the 160 in raw water (fresh water lake) no issues

 

[nola mike]

I suspect it has something to do with emissions rating original engine had one of these CARB rating star stickers on it - I want to say the 2 stars. IT was originally a 4.3/190 hp with a Mercarb that had the antitamper cover on idle mix screw. Surely set as lean as possible to pass emissions and not work after 3 years... I would think the higher temp thermostat would help emissions.

View attachment 377287 I replaced the original engine with a 5.0 w/ Edlebrock 1409 but swapped over thermostat housing etc and kept the 160 in raw water (fresh water lake) no issues

That's probably the most likely explanation, meaning it should run fine either way. Also could be that the 140 allows a higher safety margin or that running that 160 in salt could be more corrosive.

 

[QBhoy]

Ok, well... Looks like it's pretty random what got what. Newer v6/V8 trends towards 160, but many engines come with either. Older were mostly/all 140 that I see. No clear cut crossover if vortec or 4bbl. The fi models I looked at were all 160. So I stand corrected and idk if it matters.

I think you’re most likely right Mike. You’ll know more than I, for sure. I just knew that my mpi from 2003 is a 160. She runs at about 152 on the smart craft read out. Probably because of the cold water I’m in. Also aware of a few other carb (but vortec engines…not sure if that’s relevant or not) raw water that run 160 t stats. I just (probably wrongly) presumed that 160 was for raw water and 140 was closed cooling. I dare say that your understanding is likely more accurate. Never adversed to being corrected by the more experienced. All the best !