Fan or themostat? Would like to see temps drop sooner

[MacManInfi]

I have a 97 Viper with a 99 fan. The temps climb pretty high (almost to midway between 190 and 250) before the fan kicks on. The temps will instantly start to drop and they'll go down to just above 190 and turn off again. Doesn't matter what the temps are outside, if I'm moving slow in traffic, I see the same thing. On the highway it seems like the temps stay pretty solid, just above 190.

I was thinking that I wanted the fan to kick on sooner, but it seems weird to me that the fan should be able to instantly effect the temps unless the temp sender is in the radiator. If it is, then perhaps what I really need is a thermostat that opens at a lower temp?

Interestingly enough, I recently had my car at the dyno. We made two different pulls, the first one while the temps were at their peak, and then a second pull a few minutes later just after the fan had kicked off so the temps were at their lowest. You know what the difference was? 12rwhp and 13rwtrq.

-Chris

 

[Joseph Dell]

the fan is suppose to kick on at 208 and again some other time (i forget which). that is the LOW speed fan. i forget when the HIGH kicks on.

sounds like your car is perfectly normal. you could always put in a 180 thermostat... and you could even change to a different radiator. the fan is probably fine, though.

If you _really_ want the fan on sooner, DC performance does a computer update that can make it come on sooner.

good luck!

JD

 

[Tom F&L GoR]

The further from 212F your coolant temperature is, the harder it will be for water to boil off from the oil, the more unwanted chemical reactions will take place, the greater the stress on your oil and potentially the shorter the life of engine....

Could you install an oil temp gauge and see what that says, because lower temperatures aren't universally better? I suggest that because my car gained power on the dyno because even though the ('99 on a '94) fan came on, there is no coolant in the intake manifold to cool the intake air - the benefit came from the oil which was still getting warmer and thinner.

 

[got one]

Thermostat...no question. Although the fan is not too far behind...

 

[Tom F&L GoR]

>I was thinking that I wanted the fan to kick on sooner, but it seems weird to me that the fan should be able to instantly effect the temps unless the temp sender is in the radiator. <

There are three (3) sending units. One for the red idiot light, one for the gauge, and one for the PCM to monitor. On a Gen 1, the gauge sender and PCM sender are at different ends of the engine, so the gauge always reads the highest temp!!! So all those Gen 1 guys with lower thermostats are asking for oil trouble.

I think the thermostat in a Gen 2 is up front so maybe the two sending units are showing close to the same temperature, but everything is working like it's supposed to. If you want to control it more, install a manual fan switch. And an oil temp gauge.

 

[got one]

> On a Gen 1, the gauge sender and PCM sender are at different ends of the engine, so the gauge always reads the highest temp!!! So all those Gen 1 guys with lower thermostats are asking for oil trouble.

Please explain...because without it we run 220 quite frequently...with the thermostat we average 180-210 vs 190-220.

I was under the impression (based on prior posts) that running between 180 and 210 was better for the longevity of the car...

 

[grcforce327]

Read the temp from the computer,not the gauge!My fan turns on at 208 to 210 always!Purchase a scanner with real time data!!!

 

[Tom F&L GoR]

First, if I could magically separate the discussion between coolant temperature and oil temperature, I would. But since they both come in contact with that large aluminum thing called the block, they are confounded; one affects the other.

My discomfort is that it's just directionally bad for the oil to not let it warm up enough to boil off the water that accumulates. A byproduct of perfect combustion is water vapor, so there is always some water getting into the oil. Water, oil, other exhaust components combine to form sludge and acids. Yes, additives in the oil combat these effects, and oddly enough, cold oil is simulated by the industry as "Aunt Minnie" driving - back and forth to church on Sundays only so the oil never heats up. By the end of the test there is over 5% water in the form of thick jello-like sludge. Unfortunately with 10+ quarts of oil, it takes a long time for it all to reach high enough temperatures to drive off the water.

I think everyone believes running cooler provides more power. In the days of heated intake manifolds (remember carburetors) that might have been true. Your Viper intake manifold does not have a water jacket, so lower temp coolant doesn't directly produce a more dense intake charge.

Cylinder temperatures are affected by coolant; in both directions. A cooler wall will not pre-heat the intake charge. But, a hotter wall will not **** out as much of the combustion energy produced, either. If you can discuss which physical phenomena predominates, please do.

Another argument for colder thermostats is that the PCM runs richer. If it does, then you are also adding more fuel to the oil, which "uses up" other additives in the formulation.

I once had access to a good diagnostic reader that showed the temperature sensor output of both the gauge and PCM sender. In my Gen 1, the difference was about 10-12F (from front located PCM sending unit to back located gauge sending unit of engine.) If the cooling system actually opened the thermostat at 180 and kept it there, then the front of the engine is at 170F. It may sound good because your physical sense of "hot" believes you want to stay far away from boiling temperatures, but it's not so for the oil.

If the oil is kept colder, it stays thicker, too. The power gain from colder air is handicapped by colder oil; I've been to dyno tests with my car using synthetic 15W50 and during the first five pulls, I was gaining power because the oil (and transmission fluid and gear oil) was warming up. My point is that if power goes up on a dyno, it may not be just from the one thing you're looking at (coolant temp) it may be from a few other things. Every race engine I've seen numbers from targets ~230F oil and ~200F water.

I have an oil temp gauge and it takes 30-45 minutes for the oil to warm up to around 212F, so all the "boiling off" doesn't happen unless you're on a long drive. I keep coming back to this; everyone is concerned about keeping the coolant temp low but not enough about keeping the oil temp up.

The above argument may be a little disjointed, sorry. It just shows that it's not as straightforward as it seems.

 

[got one]

Thanks Tom...makes me want to go out and get a good oil temp gauge (any suggestions) and install it...now...where to put it...

 

[GTS Bruce]

Conclusionut in 180 deg stat.Have DC turn on the fans sooner.Drive it long enough to heat up the oil properly. Bruce

 

[viper spray]

My gauge reads 10 deg. hotter than the info. from the computer , I think the gauges are not spot on.

 

[Jerome Sparich]

Question for Tom

Scenario here,

Lets say we have vehicle that runs 180* water temps.

Would the water in the oil not burn off from coming in contact with engine parts that are at or over 212*?

 

[PhoenixGTS]

My experience with my cooling system (which is probably as good as it gets as far as parts go but does not have early fan turn on via PCM reprogramming) is that the thermostat does not do much if anything. No possible way my triple-pass radiator, overdrive pump, and Roe ducting kit can get anywhere close to the 180F thermostat when the ambients are over 60F or so. 190F on the guage is about the best it can do in cold weather and 200 in 80F+ weather. In other words, other than warm up/maximum temp timing my system is unaffected by having a low 180F thermostat as compared to a 190F for sure and probably even a 200F thermostat.

 

[Tom F&L GoR]

Jerome, perhaps the oil thrown on the cylinder wall might have a flash boil-off, but the oil passing through galleys and hydrodynamic bearings won't see very high temperatures until it is under the momentary extreme pressure of the minimum oil film thickness.

I also don't want to pretend there is a direct relationship that sounds like "180 thermostats WILL prevent oil from driving off water and that 195 won't." I'll go back to my rant - it is directionally bad for the oil.

It should get many to think about measuring oil temperature (don't the new Vipers have this gauge) and as PhoenixGTS explained, you can't lower the maximum temperature by lowering the minumum temperature.

 

[MacManInfi]

Awesome discussion. Thanks for the added explanation Tom. I was a little confused by your first post, but now it all makes sense for me. Good stuff!