Options for keeping Thermo fan running when engine stopped

**Cuzzo** · 05-03-2007, 05:44 PM

When the thermo is closed, doesnt the water still flow around half the system? Im saying this because the water pump runs all the time.

**love ke70** · 05-03-2007, 06:03 PM

umm, first up. how longs it been doing this for?
my car does this if the rad is over full. it finds a happy balance after a few days and have no more issues.

that is unless i give it a caining and switch it straight off.
have you thought giving it a minute or 2 to drop temps, even if water temp doesnt drop the engine bay and component temps prob will.

surprised no one has mentioned that before.

this is particularly relevant if its a turbo motor...

**MRMOPARMAN** · 05-03-2007, 06:51 PM

actually due to natural convection? the water in your cooling system does circulate, just very slowly. some cars (eg mitsubishi colt) run fans after turn off from the factory.

thats also the way vintage cars etc used to run without radiators.
so yes it is worthwhile running the fan after turn off.
ill also add an interior light delay, connected up to a relay would also do the job.
tridon switch sounds better though.

when the thermostats closed the water still circulates from the block to the head and back round again.

**ma61turbo** · 05-03-2007, 09:13 PM

I'm running the same setup as Cruz and a few others. Tridon temp switch and thermo fans powered directly from the battery. There is enough convection in the system for the fan to turn back on once or twice after it turns off the first time.

Personally I prefer this method than powering the fan from another source that gets power only when the engine is on. It helps the engine cool down better once stopped and is very, very good at stopping heat soak.

I've been told that it shouldn't be done this way, as it can lead to a cracked head but I personally call BS on this. After all, the fans will only cool the system to whatever their lower threshold is, and there is far too much natural convection(and probably still some water movement too) for it to just cool the water in the rad and not in the motor.

**ma61turbo** · 05-03-2007, 09:19 PM

Originally Posted by 1200det

Im having a issue where once the vehicle is turned off its blowing off the Radiator cap and bubbling the overflow. Vehicle doesnt get HOT nor open the Rad cap when running only after switching it off.

Recoed Radiator and New top/bottom tanks
New 1.3 Bar Radiator Cap
Completely flushed and using minimal coolant and burped several times

.

Any idea what temp the switch is? I would guess that it is a bit on the hot side and as such when you turn the motor off, and the fans turns off, all the heat still in the block causes the system to cook pretty quickly.

Whatever temp your thermostat is, I'd suggest having a switch that turns off at least 3 degrees above that. So, if your thermostat is an 85, use a 90-95 switch. If you have an 82 deg thermostat like I have, run a 85-90 switch. I've played around with a number of combinations of thermostat temps and thermoswitches and this seems to give the best results.

Add to that power from the battery and you'll be laughing.

**Norbie** · 06-03-2007, 12:32 AM

I also have the same/similar setup as Cruzida, ie mechnical thermostat wired directly to the battery, and it works great at minimising heat soak. My 2JZ used to get hot as a bastard after switching the engine off - I'd come back to the car 5 minutes later to find the temp gauge pegged at maximum! With the fans wired up directly to the battery this no longer happens, temperatures remain at the "normal" level even when the engine is off.

People often ask me if it drains the battery as the fans can cycle on and off for up to 15 minutes after shutdown, but I've never had a problem with a flat battery and I've had this setup for years now.

**clubagreenie** · 06-03-2007, 07:42 AM

I used to run this years ago. Just use one of the adjustable thermo switches available from your auto shop. They have a line that fits under the rad hose where it goes over the rad fitting and a slieeve of rubber to seal it. Works a treat and is adjustable and can be mounted out of the way (within about 500mm).

I does work to continue to cool after the engine is stopped, I had a extra temp gauge (not electric) and you could watch the temp go down (sender was located in the block) as it ran, it would climb some when it stopped, then start again and go down. Never had an issue with flat batteries etc. Would recommend.

**amichie** · 06-03-2007, 09:41 AM

Originally Posted by CrUZida

What controls the thermo now?

Mine is controlled by a Tridon switch, and the relay is powered directly from the battery, so even after the car is turned off the thermo still operates.

On a hot day it can run 2-3 more times after I have turned the car off (on for a minute, off for 3, on for 30 sec, off for 3, etc etc)

Mine is wired up like this also. Works great and in exactly the same way as Cruzida described.

BTW The fans rarely run while the engine is running. Except when the aircon pressure switch switches them on. The visco fan keeps the engine cool enough its only when you switch off that the water gets hot enough to switch the fans on.