anybody heard of running a bit hotter when running rich

I've heard of running hotter because of timing, so I guess it could be possible. But I've never heard of it.

Ofcourse, that is pretty much the way most if not all cars run...atleast at start up...see the computer finds that the cars temp is below operating temperature, so your computer tells the injectors to provide a slightly richer mixture in the combustion chamber, more gas(richer), means a slightly bigger explosion, which translates into the car getting to operating temperature faster. I would imagine that this rule would apply to everytime your car runs rich, I mean it makes sense.

Yes. Common.

Pretty good rule of thumb - richer - cooler combustion temperatures; leaner - hotter combustion temperatures.

Mike, I'm really sorry but that's absolutely not so. In this case you need to use something other than your thumb. Running too rich can cause temps to rise. It's a big problem for us red necks when we ride our dirt bikes at high altitude. The same goes for cars. Overly rich conditions will cause heat because of excess cylinder pressure due to the extra fuel that is either not burning or partially burning.

QDRHRSE - Not sure where to start -- there's lots of examples of the 'thumb' rule at work. The factory ecu on the 5.0L's injects more fuel (richer) when ACT and ECT rise above a certain level - to help cool the engine/chamber down. Any high performance tune doesn't want to go any leaner than about 12.5 or 13:1 - why? Because the extra heat in the chamber that occurs when you get leaner causes detonation -- and component problems. Look at any turbo or supercharged set up - as boost increases they ENRICH the mixture to cool temps in the chamber and reduce the chance of detonation. With all the focus on 'lean burn' engines, one of the issues to overcome is increased NOx levels - because NOx production increases with combustion temperature increase, and combustion temperatures increase with lean burn engines. A couple of blurbs from other sources (emphasis added in caps):

"When the engine is running at stoichiometric level, NOX production ranges between 1700 and 2500 parts per million (ppm). Since NOX formation is a temperature-related reaction, lean mixtures cause higher NOX production. Mixtures leaner than 14.7:1 (stoichiometry) INCREASE COMBUSTION TEMPERATURES and cause NOX production to increase. " Motor Magazine

"The ‘chemically ideal’ air-fuel mixture, by weight, in which air and gasoline are used, occurs at approximately 14.6 parts air and 1 part fuel. This chemically ideal air/fuel ratio is known as a stoichiometric mixture. Mixtures with more air are identified as lean mixtures, and tend to occur with an air/fuel ratio of greater that 14.7 to 1. A LEAN MIXTURE RESULTS IN INCREASED COMBUSTION TEMPERATURES, which allows for a more complete burn of the fuel." - Brucato PCU Overview (ecu device for Mercury V6 engines)

"Too lean a mixture (not enough fuel) causes the COMBUSTION TEMPERATURE INSIDE THE ENGINE TO INCREASE and will eventually cause the engine to lose power as well." -- from a Chrysler 2.2L/2.5L turbo site

I can go on, there are literally tens of thousands of google hits that say the same thing in case you don't buy it from me....but I think you're alone on this one.

There's lots of other variables at work when low density (high altitude) comes into play. Beyond mixture issues, less dense air transfers less heat away from fins and cooling coils. On liquid cooled bikes, less atmospheric pressure means lower boiling points, so overheating occurs at lower temps. So what's going on in the chamber as your bike runs richer isn't the only issue impacting temps.

Retarded timing will cause warmer temps for sure. I'm also of the rich=cooler/lean=warmer variety.

dastang - well, if you don't have a flow restrictor in the t'stat housing, you should get a t'stat in it - the t'stat not only regulates temps, it slows the coolant flow down allowing it to spend enough time in the radiator to transfer heat. What kind of shape was the pickup radiator in internally? Was it used? Did you have it reworked by a radiator shop? If used and not refreshed, it could be in terrible shape internally.

Not sure how to say this gracefully - so perhaps just being direct is best. Sounds like this thing is a mess on a lot of different levels. I don't think the overheating problem is the illness - I think it's the symptom. If it were mine, I believe I'd pull the motor and start fresh. At the very least - a compression check to see if cylinder pressures are even; a thorough cooling system chemical flushing; then put the new radiator/t'stat in; and be sure you have enough fan (2000-2500 cfm) to keep it good and cool. Do all your flushing/rinsing with the old components so anything broken loose doesn't clog up a new radiator. But it sounds like the block/heads could really stand to be tanked/cleaned up inside.

Well if the bottom and heads are solid - clean up the cooling system, get another radiator in it and enough fan, and it should cool.

Michael Yount said:

Any high performance tune doesn't want to go any leaner than about 12.5 or 13:1 - why? Because the extra heat in the chamber that occurs when you get leaner causes detonation -- and component problems. Look at any turbo or supercharged set up - as boost increases they ENRICH the mixture to cool temps in the chamber and reduce the chance of detonation.

Click to expand...

When I was 16 I installed a Holley carb on a 446 c.i.d. International Harvestor V-8 that was in one of my dad's dump trucks. The factory settings weren't good enough for me, I decided to tune the Holley and try to gain some extra power. I swapped the jets a few times and leaned it out too far... The result was burning the exhaust manifold gaskets right out of the motor b/c the exhaust temperatures were so high. The motor would run fine with no pops or anything but after 20-30 minutes of run time the exhaust would glow cherry red. Once I stepped it up two jet sizes and replaced the toasted gaskets it ran like a top.

Point of the story, a lean fuel/air mixture will indeed raise combustion temperatures, as Michael pointed out.

Side note: I really think that as EFI has gained more and more popularity people have really lost touch with the "basics" of engine tuning. Most of them seem to run a Mass-airflow system and hope it runs correctly. Perhaps if more people bothered to read technical manuals about their particular car stangnet wouldn't be so cluttered with inaccurate information.

anyone ever tune an air (oil) cooled motorcycle motor? i would love to see the lean is cool theory applied. as always, Mike is spot on. nice info Mike.

Got a buddy restoring an old Bridgestone 350 two stroke twin motorcycle; he's asked me to help a bit. He just replaced both pistons/cylinders. Turns out he set the floats a bit wrong, and the mixture was a bit too lean. With only about 100 yds. of warning, the motor siezed (locked up the rear tire). He got the clutch in -- and safely stopped the bike. But not before it had nearly melted a hole right through the offending cylinder's piston. He's getting good at replacing the cylinders/pistons on the bike....and at setting the float levels.

I come from DSM's and we use EGT or exhust gas temp guages. As they rise they tell use were running to lean, because lean=hotter temps. There are a few more varables that play in, but that's one way to tune, next to a wide ban. We also tune for knock which is detonation. As we make more power and our stock injectors can't keep up we get knock caused by detonation which is running a bit to lean. To get rid of the knock we add more fuel, which is what you do on most cars to tune.

So another one for lean=hot rich=cool (to a point)

Also as you go higher there is less air. As you decrease the air you keep the same amount of fuel which results in a lean mixture, which gives a hotter temp


Derek

Michael, well put. you know i was being somewhat facetious with my prior response, and your anecdote is spot on (my first bike was air/oil cooled and i became quite familiar with it).

soon2bgt said:

Also as you go higher there is less air. As you decrease the air you keep the same amount of fuel which results in a lean mixture, which gives a hotter temp


Derek

Click to expand...

Derek, i think you accidentally mis-spoke - i think you meant to say that as air density decreases (altitude increases), while fuel remains the same, the mixture turns richer than before.