anybody heard of running a bit hotter when running rich

Hissin - it may actually get a bit more complex than that for carbs. With the density decrease, the pressure differential that occurs between the carb venturi and atomospheric pressure is slightly reduced - which means slightly less fuel is pulled in than for the same volume of air being pulled in at a lower altitude. However, because of the density decrease, the MASS of air that gets pulled in at elevation is significantly less compared to the fuel that's being pulled in. Net result is they tend to run richer at altitude. Vehicles tuned to run at altitude with carbs usually have smaller jets installed to limit the fuel for a better match on a/f ratio. And of course, with less O2 and fuel going through the engine, less power is made.

Most of the overheating I've seen occurs on liquid cooled engines because 1) the engine's working real hard to climb the elevation change, and 2) the coolant boiling point is lowered because of the atmospheric pressure change at altitude - and once localized phase change occurs within the engine, things heat up quickly which causes more boiling - vicious cycle resulting in overheat. Not nearly as common in today's vehicles that operate with higher system pressures than years ago, and better radiators. Back in the day, they used to station big 55 gallon drums of water on the inclines (say in the Rockies) so vehicles could stop, let the car cool down, and refill the radiators. Of course, people used to not change oil per se - they just added it. Things have changed a bit.

QDRHRSE - you've been quiet; we don't want to lose you on this one -- you still with us?

Generally, the lower the altitude, the higher the atmospheric pressure - the higher the absolute pressure on the cooling system - the higher the boiling point. The higher the altitude, the lower the atmos/absolute pressure, the lower the boiling point. If I remember correctly, up in Vail, CO water boils at around 190F-200F - not the 212F it boils at at sea level/standard pressure. So near the gulf coast (sea level) you can follow the guide on the Prestone container as to how different mixes of antifreeze and water will impact boiling point, and it will be pretty close to what you face. However, for people in Vail, CO -- there's an adjustment to the Prestone data they have to make to figure what the boiling point of their systems are because of the lower pressure at altitude. So elevation is helping you as much as it can - drive your car to higher elevations and the problem's liable to get worse.

I think both way could be true, especially if you go extreme lean, and extreme rich.

Actually - at the extremes, no combustion occurs at all; way too rich or way too lean - and that's when the chambers get the coolest.

I am not talking about having no fuel or being flooded with fuel, I am saying basically that to rich or to lean will cause higher temps...his title says "a bit hotter", I am trying to give an example of when he may be running a "bit" hotter, it sounds to me like he is running alot hotter then he should...and the 2 cents I chipped in are based on EFI motors, not carbed, so I am probably wrong about his particular motor.

Ok, heres the answer to your questions...

Heat range

The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine head. Whether the plug is to be installed in a boat, lawnmower or racecar, it has been found the optimum combustion chamber temperature for gasoline engines is between 500°C–850°C. When it is within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits which cause fouling.

The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges. When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter.

An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate racing fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug. A rule of thumb is, one heat range colder per modification or one heat range colder for every 75–100hp you increase. In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber.

The heat range numbers used by spark plug manufacturers are not universal, by that we mean, a 10 heat range in Champion is not the same as a 10 heat range in NGK nor the same in Autolite. Some manufacturers numbering systems are opposite the other, for domestic manufacturers (Champion, Autolite, Splitfire), the higher the number, the hotter the plug. For Japanese manufacturers (NGK, Denso), the higher the number, the colder the plug.

Do not make spark plug changes at the same time as another engine modification such as injection, carburetion or timing changes as in the event of poor results, it can lead to misleading and inaccurate conclusions (an exception would be when the alternate plugs came as part of a single precalibrated upgrade kit). When making spark plug heat range changes, it is better to err on the side of too cold a plug. The worst thing that can happen from too cold a plug is a fouled spark plug, too hot a spark plug can cause severe engine damage

the next day i checked the water again and it was 1/4 emty again. it did not steam at anytime and i have no catch can at the time and there was no traces of water on the radiator nipple so i don't think it vented any out.

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You have to understand, those aren't just catch cans like the ol' days. As coolant temps. rise the overflow tank allows for the expansion and holds the extra coolant. After you park it and the temps start to drop the coolant will be drawn back into the system. You have to have the overflow, a good cap, and it all be operational. You'll have the problem you're having if not.

Michael, thanks for the Edumacation.
so on carbed vehicles, if i hear you right: as air density is decreasing (higher alt), there is some compensation occuring on the fuel side as well - being it that the means of fuel delivery in the carb, is effected itself. so the increased altitude affects both air and fuel delivery (stoichiometry) together, somewhat complimentarily.

if we were to assume that one's cooling set-up was up to par, could one run a higher pressure radiator cap to try to compensate for the lower boiling point? my recollection is that coolant does not do much at all to raise boiling temps/thresholds, vs pressure in the system. couple in the much-better heat transfer abilities of water vs coolant (IIRC, water transfers heat about 2.4 times better), then it becomes a trade off of trying to 'get by' with more water (hoping one never reaches boiling) vs running hotter with more coolant (not as much heat being transferred). this, of course, is probably moot at altitude, as it gets darn cold and a decent amount of antifreeze is needed.

interesting stuff.

i do remember the water stations in the passes of the Cascades, etc. never helped that it is always hot as all get out while pushing up those passes (at least when i was doing it).

thanks again for the tech!

Michael Yount said:

QDRHRSE - you've been quiet; we don't want to lose you on this one -- you still with us?

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Still here- a day later. Grad school is taking up most of my couch potato time. Anyway, I'm listening. In general everbody agrees lean is hot and rich is cool...except that overly rich is hot too. You brought up a good point about how that may never happen in an injected vehicle (you said this somewhat indirectly) because of the way the various sensors respond to differing conditions. However, in many (carbed for sure) applications you could see heat from running too rich. Do you disagree that a lot of extra fuel, especially unspent fuel, in a cylinder could cause more cylinder pressure? If so, would more pressure not create more heat? Before I say anything more I need to read the rest of the posts....

I'm with the "lean = hot, rich = cool" gang on this one. The extra fuel actually cools the combustion process, backwards as it sounds.


Examples:

- Headers will glow red with a lean mixture
- When a NASCAR engine runs out of fuel at speed it's very common to burn a piston

Mike,

I don't think I ever disagreed with anybody about the fact that a lean condition causes overheating, heat, engine failure....rather I said that running overly rich can cause high temps. I'd rather run a little rich than a little lean any day. Lets make sure we are all on the same page about that. The original question was "anybody heard of running a bit hotter when running rich? ". Where did anybody get the idea that I said anything about lean conditions at all. Thats not what this post is about. I read your long, and as usual, very detailed dissertation about NOX and google searches but it doesn't really apply to anything that I said. I don't see how I'm alone on this one....maybe I should have said something to the effect that "the rule of thumb" is a little general. I'm not sure. I guess that I'll keep reading....

On the combustion temp issue it's pretty straightforward -- stochiometric is the baseline (it varies a bit with temp/pressure/fuel mix/humidity/etc. but it's around 14.5:1). When there is more air than fuel - by definition lean - combustion temps rise. When there is more fuel than air - by definition rich - combustion temps drop.

On the coolant issues - it's a balance as described by hissin. Water by itself (in liquid phase) is a better heat transfer agent than the glycols mixed as antifreeze. To transfer the most heat, use water by itself. BUT - big but - you have to keep it from boiling. Because when water goes to gaseous phase (boiling) it doesn't as effectively transfer heat from the metal surrounding it. So we use glycols to keep it from freezing (which incidentally raises the boiling piont), we raise the pressure in the system to artificially raise the boiling point - so the mixture will stay in liquid phase and keep transferring heat.

MY- You know that I love and respect you but I'm going to have to lay the smack down on this one. Lets start with this little snippet from Hot Rod Magazine-try this:

http://www.hotrod.com/techarticles/54879/index1.html