MikieG1971

Today the car idled 30 minutes in 80 degree temp. Upon turning the car off, coolant overflowed from the resevoir.
What are common reasons why the fan would fail to come on?
1996 LT1 auto coup.
Thanks

belairbrian

Did you try turning on the A/C to force the fans on?
Did you check the digital temp reading in the LCD?

Could be:

fuse
fan relay
fan
temp sensor
ecm
wiring

Tom400CFI

I'm going to go ahead and say that the fans DID come on; I can't believe that you could go 30 minutes w/o massively overheating it, with no fans. Starting it "cold" -with coolant and oil at your 80˚ ambient temp, the engine should warm to 230˚F in less than 10 minutes.

I think your fans are coming on, but your cooling system needs all the same typical maintenance the many folks' do. Clean debris from in front of the radiator, and flush the system out.

MikieG1971

Fan did come on with a/c turned on. The coolant system was flushed one month ago using a cleaner and the thermostat was also replaced.

Paul Workman

Well, having recently dealt with coolant overflowing issues, some things in your initial post popped out at me:

Too "coincidental"?

IF the system was recently flushed and refilled and properly "burped", the level in the overflow reservoir shouldn't have been filled above the "COLD" line before the engine was allowed to come to operating temperature. Otherwise there won't be sufficient reserve space in the overflow reservoir for expansion, once the engine heats up!

OR...Air leaking into the system* will result in coolant not being drawn back into the system as the motor cools. (This is a major clue of air leaking into the system!) Next time the motor is started, the temp may zoom up quicker and higher than normal, and coolant overflows from the overflow reservoir, especially after the motor is shut off (trust me!).

belairbrian

OK since yours is a 96 the fans work a little different than my 92. Looking at the wiring diagram: when the system hits 219 both fans should come on at low speed. This is done by placing the fans in series using the contacts of a de-energized third relay. When High fan is commanded relays 2 and 3 energize placing the fans in parallel.

My suggestion would be verify radiator is clear of debris.

Refill cooling system.

Start car and monitor coolant temp on the LCD display. When it reaches 219 both fans should come on. If they do then you have another issue.

Could be as simple as a bad radiator cap or as bad as a bad water pump or clogged radiator.

Did you just buy this car? Has it previously worked properly? The reason I ask is if relay 3 is replaced with a 4 pin relay the low fan circuit could be disabled. At least that's the way I read the circuit.

Also a defective relay 3 could cause no low fan function.

johno504

the 1996 OBD2 cars can be reprogramed thru the ECM to turn the fans on at lower temp. even though my car has a manual fan override switch I did the reprograming and consider it money well spent.

MikieG1971

All very good suggestions. Is there a way to check these relays?
Also, what is the proper burp technique?

Mr. Peabody

As noted in post #3 & #7 you need to check to insure that the radiator is clear of debris. The system may have been flushed but if the radiator fins are clogged with debris (which VERY often they are) the system will not function properly. This also holds true if there is a bunch of debris between the AC condenser and the radiator.

On the 95 (and I believe your 96 functions the same way):
First fan comes on around 227 degrees
2nd fan does NOT come on until around 237 degrees.
BUT when car is standing still and you turn on the AC.... BOTH fans come on at their high speed. (this is pretty easy to check).

billschroeder5842

Have you checked the "in between" space for the radiator and the AC condenser? You can have a super squared away system and if the junk in between blocks your air flow, nothing will keep your car cool.

Here is what I found with my "perfectly normal" system that over heated. I cleaned out the junk and the system worked perfectly.

kenmohr

Yep me too

MikieG1971

Did you have to take it apart to get it clean?
As i said in my battery thread. I am slowely going thru this car upgrading and modernizing as i go. I am looking at going to a 3 row polished aluminum radiator, new water pump, hoses, and high performance fans.
You might say, "thats alot of $ for nothing". I am planning the powerplant overhaul. My choices are, rebuild the current LT4 to 383, 500 rwhp. This is likely to go upwards of 10k, Or..... just suck it up and drop some coin on a new GM LT4 plug and play crate engine.
A super charged 650 hp engine will probably require rear axle mods. Sounds like a fun toy huh.
With my kids all grown up, and no wife, i can finally have a cool old hotrod Corvette!!

Tom400CFI

Take the upper shroud off, then look/clean down between the rad and the AC condenser.

kenmohr

The first time I did mine I pulled the radiator