Overheating after shutdown - normal?

[NatySailor]

Hey gang,

I recently had an overheating problem which I eventually fixed. Also had a new temp gauge installed, as the old one had been broken forever.

This, FYI, is in an early model engine with no thermostat.

I have done some long motors recently (there being almost no wind on the stinking hot Chesapeake), and the engine was performing well and maintaining a constant temp of around 140 degrees.

At the end of a 2+ hour motor yesterday, I noticed that the temp ran up to about 230 degrees after I shut down. My question: is this normal? Is it normal for the temp to shoot up a bit after you shut down the engine (and hence the flow of cooling water)? Or has my overheating problem cropped up again (please say no).

Look forward to your thoughts!
Dennis

[thatch]

Dennis, This is quite normal. What is happenning is that, after shut-down without water flow, there is a transferrance of heat from the combustion chamber area (the hottest point in the engine) through the head to the gauge pickup. I'm assumming that you are using a mechanical gauge which works whether the ignition is on or off. Tom

[edwardc]

I always let the engine idle for 5 or 10 min before shutting down after a long run. The gauge goes down from 180 to ~150 when I do this.

It also gets more of that heat out of the boat instead of heating up the cabin. Not a concern on a day sail, but definitely a concern when we're out cruising.

[NatySailor]

Great news and very helpful-- thanks guys!

[JOHN COOKSON]

Remember the old time movies where the car comes racing to a stop and the radiator cap blows off and the water shoots out like a geyser?
My A4 temp goes up ~ 15 degrees when I idle back when the engine is thoroughly warmed up.

Some ideas:
Check the oil level to be sure it is not down a bit.
Idle back to ~1000 RPM for a few minuets so the heat dissipates from the engine before you shut it down.
Restrict the bypass when you idle back - if you can do so on an early model A4.
How long has it been since you have done an acid flush? The cooling system may be marginal and as a result the temp rise when going from cruise to idle is accentuated. Same for H2O pump output and slight blockages in the cooling system.

TRUE GRIT

[thatch]

I do not feel that Dennis has a problem at all. For those of us that have electric gauges, which are most of us, when we turn the ignition switch off, we have no way of seeing what the temp does, particularly where the temp sensor is reading. I always allow my engine to idle and stabilize for a few minutes at the end of a run which tends to even out the temps throughtout the engine. Parts like thrust bearings build a tremendouds amount of heat and it is the oil that removes that heat, in combination with a healthy cooling system. As a test, the next time you shut your engine down, wait about a minute and turn the ignition on and see what the temp gauge reads. Tom

[sastanley]

I always let the engine idle for 5 or 10 min before shutting down after a long run. The gauge goes down from 180 to ~150 when I do this.

It also gets more of that heat out of the boat instead of heating up the cabin. Not a concern on a day sail, but definitely a concern when we're out cruising.

+1 on this. I always let the engine idle for a bit while tying up the boat in the slip. My cruise temp is somewhere around 170°, and at idle and not under load, I can get it down to 140° in the summer before shutting it off.

Since I have FWC and an electric antifreeze circulation pump that runs on the ignition switch, I can also circulate the antifreeze around to assist further in the heat dispersion department with short 6-10 sec or so key "on" events after the engine is shut down..I can instantly see the gauge react as the coolant circulates.

Remember the old time movies where the car comes racing to a stop and the radiator cap blows off and the water shoots out like a geyser?

TRUE GRIT

When I first was building & experimenting with my FWC system, I had a metal strainer in the coolant loop to catch any leftover debris from years of RWC and keep it out of my $$ pump. I shut the motor down from a hard run at 2,000 RPM without cooling it off, and the resulting heat soak blew the seal in the strainer about 45 seconds later (which I know wasn't designed for that application anyway..) I thought the engine was on fire until I realized it was steam..

[Marian Claire]

Naty. Are you RWC? If so then as others have stated your temps seem normal. I am FWC, early model, no T-stat and my recirculating loop, not to be confused with a by-pass, is closed while in warm waters. All coolant passes thru the HX. She settles in at 165 F at cruising 1700 RPM. The oven thermometer placed on the head reads slightly above 200 F. I let her idle after getting the hook set and the temp drops to about 130. There is always a rise/spike in temp readings after shut down on my gauge. Not electric.
Edit: My temperature sensor is located at the manifold exit.
Dan
S/V Marian Claire
Back home after a wonderful cruise from NC up to the Chesapeake and back.

[sastanley]

MC, Glad you had a good trip. Sorry it was so hot here, and sorry we missed you since we never seemed to be anywhere near you while you were here!

[edwardc]

... As a test, the next time you shut your engine down, wait about a minute and turn the ignition on and see what the temp gauge reads. Tom

That's how I initially discovered the phenomenon. Shut off at the gas dock, fueled up, and turned the ignition back on to start. The overtemp alarm immediately started ringing and the gauge read over 200. Starting back up quickly brought this down and silenced the alarm (200 degree setpoint).

[thatch]

Thank's Ed, I have run accross many odd phenomenon like this over my years of tinkering with engines and mechanical things. When these things pop up, my "Sherlock Holmes" gene kicks in and I have to know why. There has been a bunch of good input on this minor subject.
Tom

[joe_db]

The way my FWC system is set up one pump goes on and off with the engine and the other one has a separate switch. Next time I shut down I'll try running the second one for a bit and see what that does to engine temps. Back in the day with turbocharged airplanes we had to idle or proceed on the ground at low power for X amount of time or the heat soak would solidify the oil in the turbo and eventually wreck the seals and bearings. Modern cars use water-cooled turbos to avoid this.

[toddster]

I used to dive with some friends who had a big motor-yacht with twin turbo diesels. Those engines always had to idle for a while at the dock before it was safe to shut them down. My friends fell for the scheme of leaving the boat with a charter company whenever they weren't using it, to "pay for" the boat loan. Among the many mishaps that befell that boat under charter was that someone ran it at full speed all the way down from Alaska, shut the engines off hot, and ruined the heads. The boat was out for a whole season.

Anyhow, when I've had a bit of overheating with the A4, if the cooling water was still running, I figured that it was better to let it idle than to just shut it off.

[epicsailin]

She settles in at 165 F at cruising 1700 RPM. The oven thermometer placed on the head reads slightly above 200 F. I let her idle after getting the hook set and the temp drops to about 130. There is always a rise/spike in temp readings after shut down on my gauge. Not electric.
Edit: My temperature sensor is located at the manifold exit.

Do you have a photo of where your temp reading sensor is located?

I have readings much higher, so I am thinking needle gauge must be reading oil temp.