Did not want to hijack someone's thread so I posted this. I understand that there is a sensor that turns on the aux fan that doesn't affect the ECM? I found a listing on eBay that might fit it. I don't feel comfortable with the temp my car runs in traffic. I may have to get my chip programmed to eliminate VATS for my alarm and I could have the main fan changed then, but Wanting a simple fix to start off with. Besides, I'd like the aux fan to come on at low temps anyway.
Advice?

http://forums.corvetteforum.com/c4-t...mp-sensor.html

 

The aux fan is noisy and with those temps listed, it will run all day long.

You may want to find something in the 210 on 195 off range.

 

What do you call "high temps" ?

Because as a new owner you are probably messing with a non-issue. Everyone freaks out when they see what NORMAL is in a Corvette. If you think yours is too hot, then you should not get in a new one...they run hotter as do most of the new performance engines. That's their nature.
These cars were designed to run stock in the 200-230 range. The main does not even come on until 228...aux fan (useless as **** on a chicken) is set to come on at 238-240. THATS normal. Your "tune" is designed around those temps. Running too cool causes problems with engine wear, fouling plugs, emissions, oil contamination etc. It ain't yer grand pa's Oldsmobile....We'll never see engines that run "normal" temps under 220 degrees, ever again. Heat has been discovered to be advantageous and the engineers have learned how to use it.

To keep a little more margin for error most folks try to stay at 210-220 with a/c in traffic and 200 cruising. Those are good numbers for most climates. Your AUX fan is not there to help the engine. It is NOT shrouded to capture the air stream and force it thru the ducts or condenser. The AUX is there as a Placebo. Early c4 owners freaked out at the new high normal temps and GM responded with this add-on aux fan...THATS why it is not part of the system. If its good for ANYTHING,. that might be to help the condenser shed some heat while you sit in traffic so the a/c system does not go to high pressure from lack of air flow. These cars were designed to be moving in order for everything to work well.. They hate traffic and get pissy if they have to idle too long.

Your aux fan is controlled by a simple on/off switch in the driver head @ #1-3. Unless your car is hitting 240 all the time in traffic or staying at 220 while cruising, I wouldn't worry over it....its normal. many folks throw that aux fan away because it does nothing to help the eng cooling and it is a blockage when its not running,...and when it runs it does not help. Just makes noise. Its a chicken tit...

remember, the thermostat only controls the MIN temp. Not the max. Your min should be at least 180...all the time. 190 is a better number for min temp.

Might want to invest the $100 in a FSM set so you can learn how and why the car works before you start falling for all the aftermarket hype?
There are endless "fixes" for non-problems with Corvettes... the manuals help you understand which are BS and which might actually be helpful. Most are BS...
Those 2 books will save you several hundred $$ the first few months.

Have fun and enjoy your car ! Just remember, its over 20 yrs old. If ANY of this were a problem, it would not have made it this long...There WILL be many other things to worry over. You will figer those out as you go.
Good luck !

 

Also consider
http://forums.corvetteforum.com/1583165063-post3.html

a common cause of higher than normal operating temps .
Many have seen a significant drop in temp as a result of cleaning the rubbish out of the front of the radiator

 

Its the hair thats found in there that always bothered me...

and trying to figure out that "bump" that I felt on the road one night last month...

 

My most interesting find was one (of two) Hostess cupcake still in the original package. Given the weight, I don't see how it could have gotten up in front of the condenser.

It amazed me how many cigarette butts I found between the condenser and radiator, along with a LOT of leaves.

 

You may be right about getting adjusted to the higher temps. Other 88 cars I've owned would be on the verge of blowing a head gasket at 220. Minimum is 180. Not happy with 238 at idle, in traffic without AC on. 210-220 is where I'd like to see it. I've always understood the reason for high temps was emissions. I agree it may be factory settings but that doesn't bring me comfort. But if you guys say the engine can take it, I won't sweat it.

 

Sent you a PM.

 

I think EVERY C4 owner ( and later models) has gone thru the exact same evolution in the acceptance of the "new normal" operating temps...

I wasted no less than Hundreds of dollars, maybe a thousand or more trying to defeat what I eventually learned was "the way it is" and its that way for GOOD REASON. I fell victim to the "old school" way of thinking and trying to apply that mentality to a modern engine/car.

Quick lesson. Took me 20 yrs to learn, here is your short cut to wealth (knowledge ) C4 cooling system in 25 words or less:

The engine temps rise and fall like the tide. Moving its fine...200 ish even in an extreme climate like Az in the summer. The car has ZERO frontal area for air induction, so it has to vacuum every breath off the hot streets. THAT helps drive temps up and keep them there while sitting still. Move it and its fine. Sit and temps will creep upward and until you get to 25-30 mph again, there is NOT enough air to feed the condenser, radiator, AND the engine air intake at the same time sitting still. The nose air box is designed to prioritize what air there is from the main fan (sucker). Radiator gets it first, air filter gets leftovers. Condenser is the last to get a taste since its non-essential to engine running or cooling. The sucker fan will draw some air thru, but its directed around the condenser thru ducts on the each side of the condenser so it gets to the radiator..... very little air actually goes THRU the condenser (idling or sitting still) to remove heat and when it does, that heat is sent directly to the radiator so the eng temp goes up even more so yours does not in the cabin......

When there is no air flowing thru the condenser, the result of that is a/c that seems to stop working at stop lites in extreme ambient temps.. it works the second the car moves again and gets fresh air on the condenser.

Now, as the car moves it feeds on as much fresh air as it wants. Plenty unless you follow too close behind a truck or some other big vehicle that gets you in the "dirty air" directly behind the other vehicle. You can follow a truck 30 ft behind it at 50 mph and overheat...because the draft is moving forward and there is no fresh air entering the nose of your car...back off 30 ft and cool off.

Your air dam is CRITICAL to good cooling in traffic and at freeway speeds. It builds high pressure in front of the dam and helps keep low pressure under the car. This helps the aerodynamics and the high pressure gets directed into the nose for cooling and eng air. Remember, every bit of air for the car has to come from below...no grill like the typical automobile.
If the air dam is damaged or missing, it will tend to overheat easily.

If you are driving in "normal" climates, 70 for the low and 85-90 high for the day, your numbers are pretty avg, maybe 5 degrees high in traffic if I read it right. If you live in the desert or the gulf coast, you have GOOD numbers...238 with a/c in 95 to 100+ ambient temps is OK ! Nothing to get excited over. Yes, we would ALL like a little more room for error. A blown hose at that temp means shut down within the next 30 seconds, regardless of where.

ex:
Mine eng is bored, got lots of goodies and it likes to get real hot.. I also have a big radiator, big hi flow pump and a redesigned hose water system to make it more efficient. I have a lot of money invested in engine temp management because I lived in Phx for a few yrs and it was BRUTAL...

BUT,
I now live along the gulf coast and the humidity is like adding 15 degrees to the ambient and our highs lately have been 100+...so my car with all that 'stuff' will sit in traffic at 235-240 with the a/c
on (of course) and even a bit higher on the worst days. Street surface temp might be as bad as 125...When your shoes start to stick to the asphalt...its hot.

The moment that I get to move again, that fresh air does what it should....my temps fall to 195-200 within 4 or 5 miles @ freeway speed. Back to normal.
I am building a REAL aux fan assy that WILL actually do something when I sit in traffic but its NOT for the engine temp, that is what it is.
My upgrade project is strictly for the a/c condenser to move enough fresh air across the entire condenser surface that it WILL keep the a/c from going high pressure while idling for 10 minutes... and cooking the driver.

Now the GOOD reasons for 200+ degree operating temps are science and not just emissions BS.
Eng oil turns to sludge when you add moisture and cook it but FAIL TO BOIL it. Boil it and the moisture disappears! The oil last longer, does not turn acidic and does not turn to goop to clog passages and trap dirt and wear metals IN the engine where you don't want them...
Let it get to 220+ ...its good for the OIL and that's GOOD for the engine !

Ever wonder how they last 200,000 + miles now? That's 1 reason why.
Another is the fuel/air ratio is easier to maintain at higher temps, giving you the advantage with better MPG. That does not automatically equal less emissions.

Decent mpg is what we want and what we get from an engine that's able to run on the minimal possible amount of fuel. Fuel cost money. It takes $50 for me to spend the day running errands anymore. That REALLY sucks...

Next reason..
fuel is a solvent. If we ran any richer, at lower temps, we would be putting raw gasoline into the cylinder and that will wash away the lube that prevents the steel on steel contact from grinding itself to pieces. That little bit of extra gas, enough to smell, will take 10's of thousands of miles off the life of a modern engine. That's why grandpa's Oldsmobile was for sale at 90,000....at 100K they ALL had to be rebuilt back in the 60s and 70s. Fuel injection ended that and high engine temps are part of this process.

What you and everyone should do, is to schedule the time to do an annual cooling system maint weekend.
Pull the top shroud to clean the dead things out, and fill a lawn bag with leaves...and gently blow the radiator veins out backwards to flush as much loose debris out as you can without folding the fins over...
get under and inside and look at ALL the small rubber heater hoses. There are a cluster of short hoses under the a/c compressor that will reach up and bite you in the *** someday...hard to access, and if they leak you had better be gifted in McGyvering stuff. Best to simply replace those hoses every few yrs before they blow.

When the shroud is off, if the radiator looks the least bit dirty inside, pull it. Its not a big deal at that point. These stock plastic tanks are throw aways, and they DO wear out. When new they work great but after 15 yrs they get tired and inefficient and need replacing. The stock radiator is $75. You can get an ALL aluminum larger radiator for $200 but that horse has been beat to death and YOU get to research which to buy.... I ain't gonna go there and start another web-brawl !

There ya go, all you need to know about C4 cooling and maintenance ...

Seriously, its not something to stress over. its just an adjustment period. Like I said before, if it were a real problem the car would have never made it this far...its been hot like that for 24 years.

Enjoy !

 

Don't believe everything you hear. The cars run too hot period. The engineers did not tune these cars optimally. Heat is the enemy period. 230 degrees is too hot for good performance. I have been custom tuning these cars for years. People who don't know any better think the factory is always correct

 

ok.

 

Especially about burning off contaminants in the oil. I had 260,000 miles on my 88 before I added custom shorty headers, a custom tune which included fan on at 210 and off at 180 and a 180 t-stat. I did this to increase power not fuel economy, and saw no change in fuel economy. I did see 247hp at the wheels on the dyno with just the above changes. I did change my aux fan switch to match and the thing ran all the time. I changed the brushes last year and now its time to change them again. It was a pain the first time because the fan motor is not supposed to be re-built and the case is spot welded closed. The aux fan was not meant to run that often.
I now have a new motor and mega ported intake system but kept the 180 t-stat. By the way, at highway speeds because of the 180 temp my egr is never commanded on. Because I tested the egr when I had the engine apart I also know it doesn't work anyway.

 

That's interesting. I looked at the code in my '86 and found these parameters that determine when EGR is commanded:

TPS > 1.95% (EGR currently commanded)
TPS > 3.13% (EGR not commanded)
MAT > 0.5°F
Coolant temperature > 56°C = 133°F

 

Yes, I saw that too. I had been chasing an intermittent EGR code for a couple of years and figured it was the temp switch, didn't really want to remove the plenum. I checked temp switch and egr solenoid and both were fine. I did a straight through drive from LA to Houston with a 195 t-stat and CEL came on every time after filling up. Before I drove back I replaced the t-stat with a 180 and the light never came on again. Its when I pulled the motor I found the EGR diaphragm had a hole in it. I need to check further because I was told the EGR command on also involved vehicle speed.

 

This is working well. I'm getting some great additional information that I'm sure will come in handy as I have no background on the C4 on which to draw. Very mechanically inclined but it helps to get info from people who have ran across this problem before.
Very helpful Forum.
Any other tips in this area?

 

Get your FSM set asap and treat it like its the Bible ! As far as Corvettes are concerned, it IS !

I was guessing for 20 yrs.

THEN I bought the real FSM set. I can honestly say that I would have saved THOUSANDS of dollars and Lord knows how many man/hrs work if I had those 2 books 15 yrs earlier...

On a C4, always diagnose with the following basic info:

fuel pressure at key ON no running.
base timing
fuel pressure at idle
inj ohms cold and hot
spark

Whenever you have a running or performance issue, the solution IS in one of those. Learn the systems and understand how they work together and how they are related. Fuel inj for example...Very temp related. Also very much integrated into other systems...
You have a handful of temp sensors...learn which ones do what and which are switches or senders.

beyond that, start doing "mock" parts searches. You WILL need that info someday. Look at FleaBay and the sellers there for many items that may be discontinued. Even good aftermarket stuff is found there. Google the online catalog stores...and most important of all,

Enjoy your car !

of the few things I have accomplished in my life, having a Corvette in my driveway for most of my adult life is one that makes me quite proud.
Have Fun !

 

On some other car forums they have the FSM available to view. I like to have the paper version but have seen the CD. What is the going price for each, and best source?