I have done a search and it really has helped alot. Definitely doing the step-by-step with trouble shooting.

Here's my issue:

96 Auto runs hot in traffic. No issues once moving above 30 mph. I replaced t-stat (even though the old one still works) and have purged the system of air.

My Questions:
How do you purge the air out of the system. Hot and Cold. Currently, I run the engine to operation Temp and then crack the screw on top of the t-stat housing. Once a solid stream of coolant comes out I re-tighten.

My fans will not turn on unless I turn on the heat!!! How do I remedy this? The temps will run all the way up to the red and the fans still will not come on. ONce I turn on the heat, they run just fine and the temps drop drastically. Once I turn off the heat the fans run for about 3-4 minutes and turn off. Once again the temps climb.

I have read many posts on this issue but sure would appreciate a real basic-to-explain answer for my questions. I'm still in Wrench 101 so speak S-L-O-W-L-Y

Thanks in advance.

 

You are doing the purge correctly. What temps are you seeing on the digital gauge? Temps in traffic between 220-230 are considered normal.

 

When I got my 96 I also thought there was something wrong with it. I never heard the fans and thought I had problems I'd attend to when I had time. However one day I said F**K it! I'm going to see how hot this gets without the air on. I never let it get over 200 without turning on the AC (I think both fans come on with the AC)

Well I sat there in the heat during a construction stop, watched the temp hit 230 and almost instantly the fans came on and the temp dropped back to 197 in a hurry. Then they shut off and repeated the cycle.

After reading a lot of heat issues here I think that's pretty normal, however when I'm done with my cam change I'm going to install a 160 T-stat, then have the ECM programmed accordingly.

Yeah, we really need to know WHAT temps we're talking about here.

 

I drove my 95 about 300 miles. Only put about 500 miles on it in a year. I installed a 180* stat about 5 months ago. My temp on the highway stayed at 190-194*. When I parked it and left it running I noticed the digital guage would get to 218* but the needle guage was more like 230*+. When ever I turn the A/C on, this actuates both fans, and my temp dropped to around 195. Any temp between 170*-230* is normal and I wouldn't worry until it gets over 230* (depends on the stat). Sounds like you got the air out. I would check inbetween the radiator and a/c condenser for trash that blocks the cooling fins. Make sure both fans come on when the a/c is turned on and look for coolant leaks. What temps is your 96 running??

 

Been dealing with the same problem for over five years. Always was told those are normal numbers, but I felt it's too warm for normal ops.

So after flushes, new hoses, new thermostat, heater core, etc. Two Saturday's ago I swapped out the radiator with brand new AC-Delco model. Since then running at fairly hot days, sitting in traffic it never goes above 201. At most speeds say from idling, 30 subdivision through 45 in local traffic it is now always 197-198, never budges. Ran a few tests down the interstate after the swap and the temps stayed right there, 197. This morning got my first real run at highway speeds a 140 mile round trip to the coast and back. From the 60's on up to 80's, the temp sits there at 197. And during a 40 mile run down I-95 I (you didn't read this) took it on up actually hit my highest yet 122. Normally if I even tried to push it before to the upper 80's-90's say it would cook up to about 215-221. Not any more and the really amazing part was 197 at 85, push right up to the triples and the temps go down, I saw it stablize there at 195. Oil temps remain constant at 215. Any time now that I get on it a little instead of getting hotter it seems to operate even more efficient and I see a 2-3 degree drop.

When I pulled the old rad out you could barely see through it. Sand and road grit over time mixed with water turn it to mud clogging up the fins. So my suspicions are that the old rad was probably operating at 50-60% efficiency.

For $149. and two jugs of coolant I finally solved my hot running C4. Now she purrs at the perfect temp in my book.

Old Rad

New Rad

 

Thanks for the prompt replies!

Temps that I'm running:

When vehicle is moving above 30 mph: 190

When vehicle is stopped in traffic for more than 10 minutes: 240

When vehicle is stopped in traffic for more than 20 minustes: 260!!!

When vehicle is climbing up a hill/mountain: 240-260!!!

I haven't noticed if both fans come on with the AC. They do with the Heat. ONce again, the fans DO NOT come on unless I turn on the heat. This just can't be right. Thanks again.

 

Well it's shut down time if your at 260!

The fans should be coming on primary 226 (No AC) on with AC, 234 for the secondary. It should hold it there.

Heat should make the fans behave similar to just vents.

A fairly easy test, start it up cold and let it idle no AC. Monitor the temps and the fan should kick on right at about 228. If it doesn't then you can let it go a little more for the second fan but if it doesn't come on you need to investigate. Right before you shut it off turn the AC on by now both fans should kick on.

Check the fuse.

The fan relays are always hot, the ECM provides the ground signal based on certain parameters. (Sorry not on the top of my head) You could have faulty relays. They are located on the drivers side of the radiator upper shroud. I don't have pricing handy but it should not be that expensive to replace the relays if necessary.

Could be a fan.

Never the less I don't believe you should be seeing those kinds of temps in stop/go traffic.

 

 

When mine was running hot, I pulled the radiator out and gave it a good cleaning. You would be suprised at how much build up is on the fins. Now mine never gets above 220 sitting in 100 degree traffic.

 

I took my radiator out and cleaned it up. It weighed about 20 lbs lighter when I put in back in because of all the little rocks that got washed out of it. C4s pick up a lot of tiny rocks in the rad because of the way the nose is shaped and the low air intake. Air curls around under the nose, picks up little rocks off the road, and lifts them up where they get ingested. I made a spoiler for the front to help reduce or eliminate that problem and bring in more air. I run 10 degrees cooler since cleaning and shrouding. Even in the hot desert heat I run pretty consistantly around 189-194. Had my computer reprogramed to turn the fans on at 210.

 

The T-stat has nothing to do with those temps. Once it opens water circulates, no matter if it is 160* or 195* t-stat. But if there is no airflow thru the radiator (an air water heat exchanger is what a radiator is) the temps will climb regardless of t-stat setting. Be sure your fans are coming on properly and that your radiator is efficient (clean and good airflow thru it).

 

I hope you got the correct thermostat, there is a special one for the LT1's. I can't remember the differance but I did read it is important. Look up LT1 fluid change , it may help.
https://www.corvetteforum.com/techti....php?TopicID=2

 

Thanks for all the replies. After changing out the t-stat (got the right one and it really wasn't the problem) and purging air out of the system, I took the car out for a spin. It's actually running two degrees cooler when above 30 mph and it's hitting 220 while in traffic and holding steady. I'll keep an eye on it but I am planning on cleaning out the radiator (though it looks pretty new) and getting a flush to the system. I'll probably add some watter wetter just for some extra insurance.

You guys really are great. I'm a member of a bunch of motorcycle boards and when you ask a question you usually get about 98% of the posts calling you a dumbass, 1% who have the same question, and the last 1% possibly giving you the answer. Once again thanks and this place kicks ***

 

My LT1 ('94) has two air bleed screws. One is on the throttle body (driver's side), and the other is on the thermostat housing. Check to see if you don't have two also. If you find another bleeder, be sure to bleed at both.

Definitely make sure both fans come on when they should.

Be well,

SJW

 

I never let mine go over 220. By then I usually have the manual fan switch on and the temp falls like the rain today

 

If the normal operating temps of the LT1/LT4 leave you uncomfortable, you can lower them by installing a 160* thermostat and reprogramming the ECM to kick the cooling fans on/off at lower temps.

I did this on my '94, and I'm very happy with the results. My primary cooling fan on/off temps are now 190*F/180*F, and the secondary fan on/off temps are 195*F/185*F.

The car now runs MUCH cooler under nearly all circumstances, and as soon as I install the new radiator that Chris May is sending me, I'm betting it'll never go above 195*F under any circumstances.

I can relax a lot more easily knowing that my cooling system has a lot more headroom before Really Bad Things begin to happen. And the lower under-hood temps should help such soft parts as hoses, gaskets, seals, etc to last longer.

Be well,

SJW

 

On the '91s we don't have a digital guage, just the analog. That would be fine with me if the analog guages were even remotely linear, but they're not. My fans come on when the guage gets very near "260*F" (The only number showing on the high side). Yet when I have brought it in for service, the GM Mechanic tells me it is running just as it should. When I sit in traffic I can hear the fans come on at the same temperature every time. The thermostat is a new GM 195* (that's Corvette spec) unit.
It's hard to accept that this is how GM designed the car, but on the other hand, it's 15 years old and still running pretty good. I guess I'll keep worrying about it until I trade it for a newer model or get so nervous about it that I re-program my ECU.
Important subject for C4s. I appreciate the post.
Glen

 

Just to clarify, the thermostatic element is still on the underside of the LT1/LT4 thermostat, just as it always was on Gen-1 SBC engines.

The element is immersed in coolant that is at engine temperature until the thermostat opens. What is different is that the thermostat on the LT1/LT4 engine regulates flow from the outlet of the radiator to the inlet of the engine, and that the LT1/LT4 'stat also regulates coolant recirculation within the engine.

The Gen-1 SBC thermostat regulated flow only through the radiator (it did not provide recirculation valving), and it regulated flow from the outlet of the engine to the inlet of the radiator.

Be well,

SJW

 

If I owned an L98, I would lower my fan on/off settings, too. Just be sure that if you do this, you don't lower the fan on/off settings to the point where the fans want to run all the time. Keep the fan/off settings at least 20*F above the thermostat temp. Obviously, if you install a lower-temp thermostat, you will be able to set the fan on/off temps lower without running into this problem.

Be well,

SJW

 

Get your PCM reprogrammed by Bryan at PCMFORLESS to turn the fans on at 208 and off at 197. They are 2 speed fans in the '96. I can't hear them on low when they engage. He can tweak the fuel air and tranny too. Mine idles prefecltly smooth now. And has crisper shifts and screams a little louder. Awesome for 4 plugs and one screw and 175 bucks.

Put a bottle or 2 of Water Wetter in there.

Check relays. Whenever the AC engages there is a pressure switch that turns the fans on high speed. 260 is way too hot. It's a pleasure to watch the temps behaving in a small range now. Cruise at 187-190, when stopped in the traffic oven it just isn't an issue. I didn't like getting pushed around by my car and forced to turn the air on to keep it from exploding a hose!

Good luck