Forcing fan on to cool engine
 

One of the downsides of grille blocks and hotter thermostats is that your engine is hotter when it is turned off. I've seen many cautions that this can cause the block to crack or other elements in the engine bay to malfunction sooner. So I've been opening my grille blocks and turning the cabin heat up about 1-2 km from home, but this usually doesn't reduce the coolant temp by more than 2-3°C.
I thought that turning the radiator fan on at a low speed would be more effective.
What do you think?

Your fan will automatically turn on and off as required to keep coolant temps at bay. I would monitor temps with an SG or equivalent. If you find the temps not dropping when the fan comes on and/or the fan staying on for large amounts of time, slightly opening the grill block will be necessary. Remember that your fan takes quite a bit of energy to run, so there has to be a balance between energy saved with the grill block and energy lost with a fan that runs more often.

Mechman, I have no problems with overheating, I'm only wondering about the effects of killing an engine which is hotter than usual. Normally, you are supposed to idle for a minute before killing the engine after a "hard workout", so that everything cools off evenly to its "natural" temperature. With a hotter t-stat, grille blocks and/or engine insulation, the "natural" temp is higher, so idling won't cool it off.

Example from my car: My normal coolant temp is 78°C, but with my winter grille block it is closer to 88-90°C. The t-stat starts to open around 83°C, but the fan normally kicks in at 97°C. (When the weather gets warm enough that the temp stays above 92°C I remove the winter grille block.) So at the end of a trip the engine temp is higher than "normal", yet not high enough for the fan to come on automatically. Killing the engine @ 90-95°C on a cold day may have worse consequences than killing it @ 78°C, so my question is: Would it be healthier (lower cracking risk) for the engine if I manually forced the fan on before parking to cool the engine ~10-15°C? I am assuming that running the fan for a minute in low speed won't make a dent in engine/battery load.

90C is about 194 which is the temperature most newer cars are supposed to run.

It takes about 107C to really damage things, staying under 100 is ideal...

Quality of oil and coolant plays in heavy here.. Are you running Blue Ice or Watter-Wetter in the cooling system? It really helps keep valve/cylinder head temps in control.

Cheers.

Dave

Dave is right. At your temps I wouldn't worry about it at all. Even on a hot shutdown.

modern cars are designed to be shut off at 110 degrees F ambient temp,with underhood heat 200 plus. This is typical conditions in the Southwest US on a hot sunny day with AC running.

You won't hurt anything with what you are doing.

Turn on the AC, that usually turns on the electric radiator fan also.

I wouldn't worry, on a good summer day my 25+ year old CJ gets up over 210F after shut down and it always has.

Its been better after I cut a large exaust vent in the hood though.

Here is my data point on this.

My minivan has a flush fitting upper grill block When it is over 90F the ambient wind will raise the temp. Head wind and it will stay less than 198. Tail wind the temp will go up to 207F. I think the cooling fan comes on at it goes back to 200.

I moved the front license plate from partially in front of lower grill up to the front grill cover. Probably I exposed about 24 sq in. more grill. The engine now runs at 195 only touching 200 when coming into towns and then going back down to 195 as I accelerate to highway speed again.

If the ambient goes to 100F who knows.

I figure that running the fan causes the engine to need to generate another 1/4-1/2 hp considering the losses.

It is truly a balancing act to get enough air flow to the radiator but not so much that it more than you need. One of the tricks is to use air that would otherwise be wasted.

open the hood