351W thermostat temps

[C Biles]

Hay fellas, I’m chasing a high temp issue with my 351W. I was seeing temps higher than 230 degrees F and figured out I hadn’t flushed my coolant in years (about 7 or 8). I found a pretty decent amount of sediment in the radiator and the coolant was spent. I pulled the radiator out and flushed it and the block. New hoses and fresh coolant and tried again. Temps have come down a little bit still regularly around 220. I’m going to replace the thermostat now thinking I might have roached it. I’m thinking about replacing it with a cooler temp range thermostat but having trouble wrapping my head around the possible benefits of it. Any advice?!

 

[ntsqd]

Need more details. Carb'd or EFI, age and type of coolant pump, type of radiator, etc.

EFI tends to run cooler so those engines can run a 190°F-195°F t-stat and be fine. Carb'd I think the warmest that I'd run would be a 180°F, but I sure wouldn't go any colder than a 160°F.

The high flow t-stats are exactly what an over-heating engine doesn't need. The reason why is that the coolant pump pressurizes the coolant in the block, which increases the boiling point inside the block. It needs a good restriction to pump against to create that pressure. The high flow t-stats are less restriction than the std t-stat, and this lowers the block pressure. If you want to dive into this deeper look up "nvrstk"'s thread on CB about his experiments with the cooling system.

I like to drill a small hole in the flange of the t-stat near the edge. Say 1/8" or smaller. I orient the t-stat with the hole at the top when installing it. The hole allows air to bleed past the t-stat. Getting an air bubble stuck behind the t-stat is a problem because the t-stat won't see the actual coolant temperature and will be slow to respond. When the heater hose pulls it's hot coolant from a fitting right behind the t-stat you can easily bleed air out of the system by loosening or removing that hose when you're filling the system.

 

[C Biles]

Need more details. Carb'd or EFI, age and type of coolant pump, type of radiator, etc.

EFI tends to run cooler so those engines can run a 190°F-195°F t-stat and be fine. Carb'd I think the warmest that I'd run would be a 180°F, but I sure wouldn't go any colder than a 160°F.

The high flow t-stats are exactly what an over-heating engine doesn't need. The reason why is that the coolant pump pressurizes the coolant in the block, which increases the boiling point inside the block. It needs a good restriction to pump against to create that pressure. The high flow t-stats are less restriction than the std t-stat, and this lowers the block pressure. If you want to dive into this deeper look up "nvrstk"'s thread on CB about his experiments with the cooling system.

I like to drill a small hole in the flange of the t-stat near the edge. Say 1/8" or smaller. I orient the t-stat with the hole at the top when installing it. The hole allows air to bleed past the t-stat. Getting an air bubble stuck behind the t-stat is a problem because the t-stat won't see the actual coolant temperature and will be slow to respond. When the heater hose pulls it's hot coolant from a fitting right behind the t-stat you can easily bleed air out of the system by loosening or removing that hose when you're filling the system.

I’m running a motorcraft 2150 carb. I had Wayne’s in Riverside rebuild the engine in 2016 and installed the water pump at that time. This is a dedicated trail rig so mileage is low but hours are higher. Maybe 200-300 hours on it. The coolant is fresh, just flushed it, also pulled the radiator and cleaned it out. The engine historically likes to run around 200-210 degF, which from what I’ve read is pretty standard for the 351W. The flow vs pressure and the boiling point makes a lot of sense, I hadn’t taken that into account. When the engine was freshly rebuilt it had a 195 tstat and didn’t have any issues with higher temps. I’ll check out the thread you suggested. Thanks!