The Stovebolt Site Forums The Shop Area Engine Shop Best cool down technique?

Gentlemen,

I have a somewhat generic automotive question, but think of it often when driving my 41...

My last approach to home includes a long steep incline. During that incline, I have noticed that the temperature guage will climb a little above normal as the engine works to pull the hill. What is the best procedure to follow before shutting the vehicle down in circumstances as described? I often let the vehicle idle for a minute or two before shutdown as I feel it allows the engine to cool. I recall in the past of heavy equipment bulldozer operators claiming that after a hard pull, an engine should be allowed to cool off before shutdown as the head temperatures will climb steeply after the water pump stops circulating water. So is this some bogus urban legend, or is there some merit?

This is reasonable. Let it idle for a few minutes.

Many for the cool down techniques are based around turbo engines..........cool down was to allow the turbo to cool down to avoid turbo bearing coking.

Ever seen/heard a car in the parking lot with the electric cooling fan running, keys out of it and engine not running? Some models do this to cool after running warm.

that will cool off the coolant in the radiator nicely. Not sure it would do much for the coolant in the water jacket with the water pump idle - unless the assumption is that water would flow by convection?

It's called thermosiphon when the coolant circulates unaided, common on old engines and less fancy stuff. Might work to some extent while the thermostat is open on a newer engine/vehicle.

I think part of the fan running is to cool the under hood/engine from the outside in addition to what might be cooled by the radiator/coolant.

If an engine is running near the pressure rating of the radiator cap when it's shut off, the heat soak after shutdown can overcome the cap spring and cause the reserve tank to fill and/or overflow. Running the fan after shutdown cools the radiator enough to prevent overflowing. A 15 PSI pressure cap will let the coolant get to 257 degrees before it boils. Most electric fans turn on at 220 degrees, and turn off again at 200. If the pressure cap is leaky, the coolant can boil before the fan ever starts to run.
Jerry

thermosiphon actually works pretty good when all parts function as designed. Some older gasoline tractors and diesel Kubota's used that priciple as they didn't even have a water pump or thermostat. Old Kubota diesels had a whistle that would start squealing if the temp got too high (envision an old tea pot).

Most engines will heat up a little hotter after shutdown as theres no air moving through the radiator for heat transfer. So it's not unusual to see the temps climb after shutdown, This is especially visable on mechanical temp gauges.

re. idle cool down. I always like to idle most all my engines down for cool off when I can. I always do this with my diesels.

I tend to park with the engine into the wind if possible, then go back out 20 minutes later to put it away. A minute or two of idle sure won't hurt.

Joe

Thanks all. The engine most in question here is a stock 1954 235 stovebolt in a 1941 truck. no electric fans, zero pound NOS AC radiator cap, stock radiator.

[img]http://www.surfacezero.com/g503/data/3764/2013-11-11_17_03_251.jpg[/img]

Just don't want to do any damage with an improper technique.

Cylinder head temperatures do climb some after shutdown. Most of the time after the engine has been working to its limit, a minute or two of idling brings the temp down enough so that on shutdown you don't start boiling. On my truck, if its above 105F out and I've been driving at highway speeds and pull in someplace and park, if I don't idle a few minutes before shutting down, I see a spike from about 190F to about 220F fairly quickly right after shutdown and can start my unpressurized system to slightly boiling. (I do run antifreeze) A minute or two of idling and this doesn't happen, but there is still a rise, just not enough to boil anything. I try to avoid shutdowns without idling unless its cold outside and the thermostat is already closing as I'm parking. Even in the wintertime the temp rise on shutdown is still there, just doesn't get to the boiling point. I suppose if the temperature gets high enough quickly enough it can stress something enough to potentially crack something.