You may have seen my recent thread on insulating the maf from underhood heat to hold a more consistent afr in open loop tuning. So far so good. On a 'vette, the underhood area is so tight and sealed up so well, the heat just can't get out, especially with the thick fiberglass clamshell shaped hood sealed up on sides and windshield end.

I run a 160 thermostat. Fan turns on at 180 and off at 170. When hot out it runs all the time. I think it can't pull enough air through the radiator because there is nowhere for it to escape in the sealed up underhood of a 'vette. So now, I cut down the seal at the cowl so air can escape, and I removed the seals where the inner fender tops meet the bottoms. Will allow some air to escape. (on a 'vette the inner fenders are attached to the hood and go up when the hood is open. Since my car is a fair weather car, I may remove the inner fenders completely if it still isn't getting enough ventilation under the hood.)

My question is, I've been told that a fan running can be an airflow restriction at higher speeds. Anyone know about what that speed would be? What I'm doing (6E ARAP based tune) is setting the Fan1 DC Table Mph Min to whatever speed that is (I'm guessing around 50 mph), and I'm setting the Fan DC vs Coolant Temp table to all 0's. Should effectively turn the fan off when the min mph to use that table is reached. Anyone have any input at what mph I should try to get my fan to turn off?

 

i don't see the fan being a restriction at higher MPH, unless the fan is in front of the radiator... in which case it will always be a restriction.

and the 89-90 turbo grand prixs had some interesting stuff like this...there was a fan that turned on at roughly 120*F and never shut off unless you were above ~50MPH to keep the intercooler at a better temperature. i think the only reason why it shut off at 50 was because there was already enough airflow to keep it cool without assistance.

and then there was the regular fan as well, which turned on ~20-25*Fabove the thermostat setting...

 

I put some L-something fans on my vehicle.

All "newer" vehicles are probably pretty similar in that underhood heat has only one real escape path, down.

When my fan comes on (never had it get hot enough to activate the second) you can feel the hot air coming out behind the front tires between the rocker panel and the ground.

My understanding is that the electric fan should "overrun" if it's on and incoming air surpasses the blade speed. Nonetheless, the fan SHOULDN'T be on IMO if the vehicle is moving anyways, at least not after a few seconds of moving.

As efficient as a fan is, at any sort of vehicle speeds where drag *may* be an issue, it should take at best seconds for engine temp to get back under control, assuming a good radiator.

Wrong forum methinks.

 

I appreciate your information and reply. But......Wrong forum because it's a Corvette? It's about the same as a 3rd gen Camaro in most all aspects. There is not a Corvette forum anywhere with people that have anywhere the tuning knowledge that is here. And nobody here cares what your engine is in, they will help you tune it. Well, almost nobody cares I guess.

 

This is kind of what I'm thinking, at what mph (i was guessing about 50) would the fan either be a restriction or may as well not be running because it isn't doing anything besides using electrical power and putting undue wear on itself. Sounds like, in that application, they were also thinking 50 mph.

 

i don't know much about vette aerodynamics, but what is it set at in the factory tune? that should give you a good idea of what the GM engineers thought was a good setting.

 

Well, that is the problem. Stock, it is set to start looking at the duty cycle table at anything over 35 mph. Then, the duty cycle table is all 100% DC. So basically, they had it set that the fans would run once the fan on temp was reached, no matter what the vehicle speed, unless it cooled down enough to reach the fan off temp.

 

i honestly wouldn't find that to be an issue for me, since it guarantees temperature control. and as long as your fan(s) are working correctly and there is no kind of blockage to the radiator, when you're at speed, it will cool off to just above/under/around the thermostat rating. that's why i have my #1 fan kick on 15*F above the stat rating(and where the temp stays at a steady 55MPH cruise) and then off again 10*F above the stat rating. my fan #2 is set similarly: 20*F above stat, off at 15*F above stat.

this way, i'm always between 195 and 210*F.... heat cycling is killer.

 

I'm going to try a window like that cause I just tried my way, and the fan won't kick on. Even though it isn't suppose to look at the fan DC table until above the min MPH setting, the fan won't kick on if the DC table is zero'd out. Wanted to post the results before anyone else tried this.

 

No, I just figured aerodynamics and the physics of fan restriction are probably more at home in the cooling forum. I understand the tie-in, and see that you are dealing with the PROM as well, but people that deal with cooling a lot more are probably lurking in the cooling forum, and you may get more responses there, at least in regards to the physics of cooling/fan operation, etc.

I removed the stock fan from my vehicle and tested that way. Over 25MPH there was no need for it at relatively "light" engine load (about 70* ambient).

I did however decrease the fan cut in temperature in the PROM a bit, so that the engine temp at idle didn't swing so much. The lower your t-stat rating/fan-on temp, the harder your electrical system/fan is going to have to work.

Have you done an underhood temp measurement and got feedback on what others are seeing? How about IAT, comparing to what others see with X* ambient at idle? To be honest, I'd expect a Vette and Thirdgen Camaro to be pretty similar in regards to underhood heat at idle. Sounds like you've made progress on the MAF/heat issue, so that may indeed be it, but it would SEEM that the problem would be more widespread among MAF owners if it were "normal" of the components to respond to heat as you are seeing.

Note that far from being an application snob, my signature makes no mention of the vehicle that my setup is installed in.

 

Cool, no problem. I was hoping you weren't upset about what my car my engine is in.

I don't have an overheating problem, am just trying to minimize the underhood temps and coolant temps as much as possible. I'm not sure about the 3rd gen camaros but I know the 'vettes are sealed tight under the hood. A very high compression 383, coupled with the headers, do generate alot of underhood heat. Not sure how much as I haven't checked it yet, but much more than I've felt on other vehicles. I believe with opening the cowl area and about a 1" gap in the front wheelwells, it will work good. It is drifing alot of hot air out in both those places now when idling, and when the fan kicks on it is amazing the heat that blows out in those locations. I have a couple other things I might do if I still feel too hot under the hood but I think I'll be satisfied now.

My IAT's have always seemed pretty normal, but my sensor is relocated to the air intake as the temp would drop like a rock while spraying nitrous when it was located in the plenum. Doesn't matter alot, but for datalogs I wanted to see the incoming air temp, not the temperature drop nitrous causes.

I think I'm going to take Saar's advice on fan settings, and not worry if in fact it does run once in a while while driving down the highway. For the most part those settings should keep it off while on the highway. I have a 160 stat. I set the fan on at 180 and the fan off at 175. Just watched it idling in the driveway for a while and it is cycling on and off nicely. Not on and off as quick as I thought with the settings only 5 degrees apart, which is a good thing.

 

An easy and effective method to turn the fan off above 11 mph (or whatever speed is desired) already exists in the 165 ecm masked bins (32, 32B, 6E).

Simply raise the AC off fan on/off settings by maybe 20 degrees relative to the AC on fan on/off settings.

Below 11 mph, the AC on fan settings are always used. Once 11 mph is exceeded, the AC off fan settings will instead be used when the AC is off.

This creates a window in which the fan will be turned off above 11 mph until the now elevated AC off fan on temperature is exceeded, assuming that the AC is off. This method will still provide protection for very high temperatures when above 11 mph, based upon the chosen settings.

You can adjust the 11 mph threshold to move the switch point around as desired, and also adjust the 15 second delay time, so that the fan can turn off quickly, once the off conditions are fullfilled.

In my own car, I turn the main fan off above 5 mph after a 2 second delay by this method.

I have roughly a 20 degree window between the settings in which the main fan will stay off between approximately 185 and 205 F when moving faster than 5 mph.

Adjust your settings as desired to suit your needs.

There is also a 35 mph speed threshold that only affects the duty cycle if the AC high pressure switch/flag is set. Below 35 mph a constant fixed duty cycle is used to ensure sufficient cooling. All other conditions make use of the variable duty cycle vs coolant temperature table.

Changes in the duty cycle table will affect normal fan operation at all speeds, except for the special condition of AC high pressure below 35 mph.

 

WOW, very informative post. Thanks! Think I'll give that a try. So, you say 11mph, because the "Fan1 Turn on A/C On < mph" is set to 11 in the stock bin.

So, if I set that to say 45mph, then set the A/C on setting to on at 180 and off at 170, then set the fan off settings to on at 210 and off at 205, that will effectively shut my fan off when above 45 mph unless the temp reaches 215?? But it will kick on at 175 degrees anytime I'm below 45 mph?

If so, that is exactly what I'm looking for. I realize that, with a fan on at 180 and off at 170, the fan will run almost all the time when I'm below 45 mph, but that is fine, it will help extract underhood heat. But, with on at 210 and off at 205, the fan should prettymuch never run when above 45 mph, which is what I'm looking for.

 

Yes. You've got it.

You may also want to reduce the 15 second off delay, so that the fan will turn off sooner once you exceed 45 mph with your example settings.

Just monitor the cooling fan duty cycle when logging data, and it should be obvious as to how its working.

 

Just started it up in the driveway and idled it up to 180, and the fan kicked on, even with the A/C off. You are right. Thanks for the info! Who would have thought it uses the A/C on settings even with the A/C off when below the mph set in that constant.

Thanks again! Hopefully this info will help others too.

 

This is good reading, and interesting. I might have to adjust some things. Currently I run 170 tstat, fan on at 187, off at 185(184 w/AC), min 40mph for DC table, 15 sec on min, and 20mph for turn on w/AC on. For my DC table, i set to 0 at 176, 50% at 198, and 100 for the rest. I was having my fan come on alot, and I dont think you need it on for when the car is moving good. Now I have 2 lights in dash wired up to let me know when either fan comes on. And I dont think my min 40mph setting is working. Now I realize that only tells you when to use the DC table. Might have to adjsut the other mph setting, as well as temp settings. I think a 10deg temp window swing is too wide. Actual coolant temps take a good bit of time to move.
My ride used to run real cool, until I installed the high-stall TC. Now going up hills she heats up quick. So I was adjusting the fan stuff. And my fan still runs when I am cruising more than 40. I really dont want that.
good post here.
I think the guy who said 'wrong forum' meant this post should be in the 'cooling' forum.

 

I set my fan settings as described in post #13, then drove around alot on a very hot day this weekend. I found that from 45 to about 60 or so mph it heated up more than before. At 65 and above all is good. Seems for me (keep in mind this is a 'vette), 65 mph is the majic number in which the air is coming in fast enough to not need the fan. IF the fan runs above 65 mph there is no difference from it not running. Below 60 or so, it runs hotter if fan isn't running.

Now, in a Camaro, I've been told there is more underrhood air moving and more air coming through the radiator at highway speeds. It would appear that is true but I don't have any tests or evidence. I like having the fans set up this way, but anyone doing this would want to record engine temps with the fans running all the time at different highway speeds, then set the fans to turn off at a certain speed, record again, and keep lowering when the fans kick off until a difference is noticed in the coolant temps.

 

Another item to keep an eye out for is debris build up. The area between the A/C condenser and radiator likes to collect junk. At about 60K miles my '92 had that area was about 1/3 of the way filled. Pieces of Styrofoam cups, pieces of paper, leaves, straw, and other assorted items.

I had started to notice that the engine was running warmer and warmer. Which lead me to do some checking. Which I then found the debris trap.

This ECM also has no MPH fan cut off. It is entirely based on CTS and the A/C activity.

RBob.

 

Yes, very important here. I have the same buildup, mainly leaves. Took me a while to figure it out. Maybe found it when I had to do radiator repairs. Didnt notice that much of temp rise however. Every year I just take the top rad support plate off, and just push the radiator a little out of way, and clean the debris out. Just use a good air tool with long handle.

Just burned new chip raising the AC off fan temps. Left the min speed set to 20mph, but changed fan run time down to 10seconds. Also made other changes in bin. Will test it out tomorrow.
This is good stuff.

 

Yes, but as tequilaboy explained, you can set the mph at which it uses the a/c off setting, and everything below that it uses the a/c on fan settings, even if the a/c is off. So basically you can set it up with a MPH fan cut off. Kind of weird that it is set up that way but I confirmed that it is.