water blowing back into overflow tank

[swump_man]

When i am running temp runs between 180 to 200 up and down. when i run her hard and shut her down the water bubbles back up to the overflow tank. any ideas????

 

[K-mac]

When you shut down your engine, your water pump stops moving water
your cooling system stops working. The block which is much hotter
than the coolant will continue to heat the coolant, causing expansion
and thus the over flow. Check your radiator cap, make sure it holds
the proper pressure before release. also you might allow your engine
to idle for a few minutes and cool down before you shut down.
Those electric water pumps and cooling fans are great for that,
they will keep cooling after you shut er down.

 

[Olf Art]

Just my opinion, Swump ..... 180-200 deg. is too hot for an airboat. The heads will be a lot hotter than 200, and as you know water boils at 212 deg. at sea level.

My boat runs at around 150-160 deg. on the guage so it never boils the coolant.
Are you running a thermostat ?

 

[fatboy0054]

Let it idle a little before shut down !

 

[swump_man]

doyou think i might need to change my thermostat to a lower temp to open. i think there is a 190 in it

 

[Airboatcapt2]

Here is a start:

Make sure your Radiator is clean, and the fins are too damaged. I would put a 165 Thermostat, and make your your belts are good and tight.

 

[Cadillac Performance Pts.]

Do any of you older gentlemen remember when cars didn't have overflow ttanks? That's what they are for. Like K said, check your cap as this is normal after shutoff for heat soak. I remember when full service gas stations checked water AND oil when cars had no overflow tanks.

 

[Rich Andrews]

so me running my 383 crate engine with a 180 thermostat is no good?

 

[jdotson]

I run a 180 thermo in my setup as I want the temp to get high enough to rid the block of condensation and moisture build up in the oil. Running temps reach about 195 - 200 after dry running, sometimes reach 210 but I always let the engine idle for a bit after hard running to circulate the water/coolant before shutdown. I'm still considering an electric fan for idle cool downs as the prop/ratios these days just don't seem to pull as much air for cool down at idle rpm's.

 

[Rich Andrews]

GM told me 180 was about 20 degrees colder than the cars that run those engines operate at...

 

[Airboatcapt2]

Rich 180 is fine, If it works for you. I like the 165 in lots of boats. I dont want my engines getting 200+ degrees. If a chevy Big block is hitting 210+ degrees and you idle it will most likely just get hotter. You gotta kick your RPM's up to like 2500 to let the prop drag enough air across the motor to cool it down.

We run an Aluminum Expansion tank and a plastic day tank. It is not a problem for a little water to flow back into you day tank thats what it's there for. I just didnt like the idea of a chev. getting 200+ degrees. The aluminum Heads or blocks are not as forgiving to high temps.

Watch your guages, if your breaking 200 degrees you need to find out why and cool it down.

 

[Cadillac Performance Pts.]

Sounds like airboatcapt. has been there, done that. Our situations on dry ground typically like 200 plus, but we don't have a 5 foot fan running across the motor. What we have seen, an engine wants 160 degrees in the comb chamber area and 240 in the block. That's real world wants from any top builder. It's hard to duplicate w/o 2 cooling systems. In a dyno supplied world, it's natural. Only to take advantage of it with reverse flow cooling. Hard to do in regular conditions. In a drag race situation, a Cadillac iron head engine gets faster with each 10 degree increment. All the way to 240 in a pressurized system.