Engine efficiency improvement through higher temp thermostat?

[diesel_john]

I run pure Seirra antifreeze in a cast iron block with aluminum heads. i did it to help prevent detonation. I boiled the water out of the mixture by turning off the fans and taking off the rad cap and letting ti idle until it got to 250 f and there were no more bubbles coming out. It doesn't even boil at 250 now with the cap off. no steam separation in the heads equals a better resistant to detontion. the solution is a little bit more viscous than 50/50 make sure you have a good enough water pump on cold starts to circulate in the block and the stock thermostat will run hotter because of this. i always take out the thermostat and drill a 1/16th hole thur it if its doesn't have a little air bypass check valve built in.

[elhigh]

Originally Posted by Lazarus

Actually I have done this with no affect on FE. Tested it up to 60 mph with no increase.

Ah, well. Ford did it on some of their old Falcon stock cars and it seemed to work well for them - it looked like a car with four headlights, but two of the "lights" were just big holes ducted back to the carbs.

I guess there just isn't enough dynamic effect at the kind of speeds we mere mortals have to drive.

[NoCO2]

Originally Posted by elhigh

Ah, well. Ford did it on some of their old Falcon stock cars and it seemed to work well for them - it looked like a car with four headlights, but two of the "lights" were just big holes ducted back to the carbs.

I guess there just isn't enough dynamic effect at the kind of speeds we mere mortals have to drive.

It WOULD have somewhat of an effect at the speeds of race cars purely because they are going 150mph+ in most cases. You have to think though, superchargers spin at speeds approaching 15k-20k RPMs, with that kind of rotation, you get a lot more air then just forcing it in with what you're talking about which is essentially a "ram air" system where the air is being forced in because of your speed.

You're right, at normal, "mortal" speeds you will likely not see any improvement, you may see something at 80+ which is still pretty average (around where I live) for most people to be traveling on the freeway, but no one here is "normal" in that respect I don't believe.

[8307c4]

All I know is you want neither the coolest nor the hottest thermostat under the hood, neither of those are meant for any situation except one that specifically calls for it.

On some older cars it has been known the cooler thermostat extends engine life at the cost of some minor mpg loss yes, but the hottest one is as likely to create strains and pressures that may result in premature failure of hoses and pumps and whatever else could go, because as temps increase so does psi.

That having been said I think on most vehicles the second hottest should do well, but I wouldn't push it beyond this.

[ECONORAM]

I realize this thread has been dormant a while, but it touches a few things I have been stewing over.

Originally Posted by BIG DAVE

I use a 203 degree thermostat, and Evans propylene/ethylene glycol coolant.

I gained 0.5 MPG by doing this. One of the few engine mods I've seen work.

Originally Posted by diesel_john

I run pure Seirra antifreeze in a cast iron block with aluminum heads. i did it to help prevent detonation. I boiled the water out of the mixture by turning off the fans and taking off the rad cap and letting ti idle until it got to 250 f and there were no more bubbles coming out. It doesn't even boil at 250 now with the cap off. no steam separation in the heads equals a better resistant to detontion. the solution is a little bit more viscous than 50/50 make sure you have a good enough water pump on cold starts to circulate in the block and the stock thermostat will run hotter because of this. i always take out the thermostat and drill a 1/16th hole thur it if its doesn't have a little air bypass check valve built in.

I realize both of your vehicles are diesels. I was also thinking of switching to Evans Engineering coolant, but I think my truck would require a custom tune to take advantage of the added temperature range. (OEM T-stat is 193.) I thought it might also give an mpg boost, since it'd be retaining more of the combustion energy...instead of wasting it by cooling.
Never thought of drilling a pilot hole in the T-stat. Did you do that even before the coolant swap? I did think about redesigning a T-stat, so it was a butterfly valve that pivoted like a throttle plate, instead of that blob in the pipe...but that would take some work.

Originally Posted by MetroMPG

I can't answer the thermal stress question, but do have another one: will your engine let you run at higher temps? What's your electric fan's trigger temp?

Temp is a tricky issue because another effect of more heat is less timing advance (engine may be more likely to ping the hotter it gets).

I'd like to raise my truck's running temps to pursue better mpg, but my truck's PCM will pull timing if the water temp is too high. I have installed a warm air intake and an under drive crank pulley. The Taurus e-fan keeps temps in check, but the WAI makes the tranny downshift out of 5th lock sooner (grrrr).

Evans advises everyone using it to run a non-pressure coolant cap, or the fluid will never boil...which would make it less effective. I don't think gaskets would be a problem with Evans coolant (boils at 375* at 0 psi), but the timing loss in my truck would make it a dismal mod, I think. And...just because the coolant is hotter doesn't mean combustion is any hotter, does it? Hmmm, might even be able to delete the radiator fan...would definitely need a digital temp gauge.

[cptsideways]

My Lupo3L Tdi apparently has a 92deg stat, it definately runs in the mid 90's once warmed up (eventually)

[aerohead]

Originally Posted by Lazarus

The hotter the engine the more effecient. I'm currently running water temps of 200-207. If I bumped that up to 215-220 and ran a high quaility coolant. What kind of bump in FE do you think? At what temp would the head gasket become a concern.

The only relationship that I know of,is raising the temp in the combustion process with high-temp metalurgy or ceramics such that the delta-T is actually increased and waste heat eliminated.An adiabatic cycle.No cooling system.
Experimental engines have been tested.Nitrogen oxides were an issue at temps where 'inert' gases begin to react.
Vapor-phase or dry lubrication is also of interest.
Be careful.

[8307c4]

It's funny how over the years the one thing I found with absolute consistency is that nothing, absolutely nothing comes without some sort of side effect.

Anything I do that saves fuel ends up costing me elsewhere.
And in most cases, it costs way more than fuel I ever saved.

In this particular case I learned (especially with trucks) that higher engine temperatures usually results in higher transmission temperatures... The transmission sits right behind and below the engine, a lot of the engine's heat gets transferred to it, the hotter the engine runs, the faster the transmission warms up.

I hope I don't have to get into what happens to an automatic transmission when it gets too hot, but lets just say they quoted me north of $2000 for a rebuild and I am now running a low temp 160F degree thermostat.

[arcosine]

I had my corvair engine running pretty hot, maybe 230Fto 240F enough to make new o-rings hard as rock in a month (this happens at over 225F for buna-N).

[yoyoyoda]

Originally Posted by 8307c4

I hope I don't have to get into what happens to an automatic transmission when it gets too hot, but lets just say they quoted me north of $2000 for a rebuild and I am now running a low temp 160F degree thermostat.

I realized that this forum doesn't actually know that much about automatic transmissions, despite the damage that can be caused with their unsafe operating temperatures. For example a front full grille block, I would like to see what temperatures their transmissions are running at...

Sorry to hear that yours was damaged.