E.O.C. cracking heads?

[scissorhands]

In theory wouldnt engine off cruising have the potential to crack engine blocks or heads? Say the engine off radiator water cools dramatically in cold weather down a big mountain road, and then you start the hot (though cooled somewhat from the wind coming down the mountain road) engine and draw cold water into a hot motor...

[SVOboy]

I wonder if the thermostat would close off circulation if you really cooled down the coolant that much...

Anyway, I can see that being an issue, though most of us are prolly running full or close to full radiator blocks during the winter, anyway.

[Daox]

Nah, the thermostat is a mechanical device that works independantly of anything else. Theres no chance of cracking a head.

[jamesqf]

The motor will cool off about as fast as the radiator coolant. Insight temp (via Scangauge) will drop down to 130 or so on a long downhill, even in summer. Other vehicles will show the same sort of drop on dash gauge (though no numbers), and the temp pickup is usually on the block near the coolant outlet.

[Gregte]

Originally Posted by scissorhands

In theory wouldnt engine off cruising have the potential to crack engine blocks or heads? S...

My thinking is, if that condition was enough to crack the block or heads then they would already be cracked from normal driving.

The first time the thermostat opens, after you begin your morning commute, the radiator has coolant that is the temperature of the out of doors, perhaps as low as -20F on a December morning. But at some point the T-stat opens (engine finally reaches +195F) and the cold coolant rushes in. But alas the engine survives it, day after day.

For that matter, I expect the radiator coolant probably cools back down to near -20F every time between when the T-stat closes and then again opens, at least on a -20F winter day.

[scissorhands]

Your right in that the engine survives these fluctuations, everyday, with no problems. An engine draws cool water from the bottom of the radiator via the impeller wheel on the water pump and the thermostat is like a tap controlled by temperature. The thermostat is located at the point where water exits the engine back to the radiator, normally at the highest position on the head. I have descended hills in neutral with engine on for years in my auto transmission Toyota diesel van. After descent is over and I engage drive I notice the water temp dives quickly. The sensor is mounted in the lower portion of radiator. HOW ABOUT a thin film wind cutting curtain that closes the front grill to maintain coolant temperature would not only conserve warmth in the heated engine etc, but also improve aerodynamics of the car (both increasing mpg and coast time/distance). It closure and opening could be temperature controlled or manually done with a piece of string. Moving off when cold one could keep the engine bay shut so no windage would work to cool engine until ideal operating temp was reached. In cooler or wintery conditions in could be partially or fully shut at times and would minimise heat loss and improve engine performance, mpg, drag

[roflwaffle]

The only thing I've read about is a cracked radiator.

[scissorhands]

I'm having no end of trouble with the site. Temp pickup on thermostat housing (it was late last night...)

[IndyIan]

Originally Posted by Gregte

My thinking is, if that condition was enough to crack the block or heads then they would already be cracked from normal driving.

The first time the thermostat opens, after you begin your morning commute, the radiator has coolant that is the temperature of the out of doors, perhaps as low as -20F on a December morning. But at some point the T-stat opens (engine finally reaches +195F) and the cold coolant rushes in. But alas the engine survives it, day after day.

For that matter, I expect the radiator coolant probably cools back down to near -20F every time between when the T-stat closes and then again opens, at least on a -20F winter day.

I haven't looked at my cars myself but someone posted recently here that the coolant is pumped through the heater radiator all the time as it by passes the thermostat. Also the thermostat doesn't pop open, it opens gradually and I also doubt it closes completely on most cars so it shouldn't be a huge temp difference.
I agree though that any production car engine shouldn't mind EOC, highly tuned motorcycle engines for example may not like the same treatment but they produce so much more hp per litre.
Ian