thermal shock after shutdown and restart?

[gold-n-rod]

Here's something I don't really understand. It happens on both my boats.

1. run boat hard
2. shut down for 10 minutes
3. restart boat
4. steam comes from exhaust and the temp climbs a bit (150* to 165*)
5. after a couple of minutes, the temps drop and the steam ceases.

Wouldn't this be hard on an engine? The hot cooling water remains in the engine while shut down. Once restarted, cold lakewater (+/-60*) is now circulated thru the hot engine. The hot water exits as steam. Isn't this a hell of a thermal shock to the engine?

Just wondering. If it's a bad thing, how does one prevent it, short of a closed system?

:wavey:

[Ed Donnelly]

The thermostat would prevent an onrush of cold lake water through the engine,as the air bleed holes on the thermostat aren't that large. The main water flow on start up would be through the manifolds...Ed

[oldandtired]

You really should let any engine idle for a bit before shutting down, especially if you were just running it hard. When you shut the boat down, the water will run out of the engine to whatever level it can. Generally that means that your risers and maybe heads will drain. If the engine was run really hard and shut down without letting it stabilize, it could cause some problems. I've never had this problem with the boat ( mainly because I am surrounded by idle zones) but my jetski can be overheated like this really easy.

Rene

[blackhawk]

I always let my boats run at a high idle(1000rpm) for a couple minutes after a hard run. If it was a long run(10+ miles) at WFO I will let it idle a little longer.

[tiger lily]

on some of my other play toys(trucks, quads) after hard runs at the sand dunes and shutting them down to hear someone over them, you will see on the temp gauge that the motor actually gets HOTTER once its off because the coolant quit pumping through the motor, after you fire it back up and get the water pump moving again, they come right back down, a good way to pop a headgasket or crack a head.

[BigGrizzly]

Oldand tired is correct. the engine gets hotwhen sitting after a high speed shut down cool down at idle before shutting off. This will save the engine and stop that problem. Think what would happen to a really hot glass plunged into ice water. Nothing else to say is there

[CHACHI]

It's called "heat soak". Car turbos are canidates for the same type of issues. but in a turbo the oil get super hot and then "cokes" forming hard deposits in the oil, and on re-start these small deposits take out the turbo bearing. Thats why after a real hard run with a turbo, you let the engine idle to remove any excess heat to prevent this from happening. Ken