My daily driver 1993 LT1 has been having some overheating issues and getting way up to 250 (I didn't want to find out just how high it would go ). Last week, my low coolant light came on.

Discovered one of the hoses from the radiator had a hole in it. So fine, replaced that. New coolant. All taken care of. Ran perfectly all this last week with temps at around 190. So today, I take a buddy of mine to a congested part of town. Sure enough (and almost to the exact minute that I started having trouble last week ), I look down to find the temp was up to around 250. I also noticed that my battery voltage was down. The fans also didn't seem to be running. And of course, driving on the freeway back to my place was fine - the only thing I had done was let it sit for about 40 minutes and had tapped on the thermostat housing haha. All hoses were fine and there was plenty of coolant.

Right now, my dad and I are trying to run diagnostics and it's been a while since we've been into the FSM because my car's been so reliable so I may end up asking some stupid questions...

We've checked the fuses and no problems there. Now we'd like to run diagnostics on the fan itself and the FSM keeps saying to ground the "diagnostic test terminal" to make the fans come on but we haven't found anything on where that is... maybe this is a stupid/duh! question but can someone fill us in on where the diagnostic test terminal is?

Any additional advice/comments? I need it quick since this is my dd and the only vehicle available to me!

 

There's a connector on the right bottom of the trim panel under the steering wheel. It should have a black cover over it. Pull the cover and jumper terminal A to B. They're hard to read but you can see them. Then turn on the ignition but don't start the engine. The fans should come on and the check engine light will begin to flash code 12 .... once .... pause .... twice .... pause etc. It will repeat this three times and then flash other codes if there are any. Note these codes and repost. We'll tell you what the codes mean. The thing you're looking for is the fans. They will come on when you jumper pin A to B. If not repost the results and we'll go from there. Good Luck

 

In volts, low isn't a number. Normal dash voltmeter reading is 14.3 volts engine cold and the alternator output drops to 13.3 volts as it gets to its operating temperature. Lower than about 13 volts and you have an alternator that needs service or replacement. C4's suck up debris and jam it into the lower part of your radiator and block that portion of the radiator from its ability to transfer heat out of the coolant. Guess what happens when you install a small radiator in your car? With no or little airflow, your coolant temp goes way up. Remove all the screws from the top cover over the a/c condenser and the radiator and look down between them and my money is on you finding debris jammed into the lower part of the radiator. Get it out of there and you will go back to normal coolant temps. Also, your fans start running at 228F and if they don't, then you need to find out why. Read your FSM for diagnostic procedure for your cooling fans. I have an 87 vette as a DD and I had to install a new fan motor years ago. These are d.c. motors with brushes and the brushes don't last forever.

 

Thanks for the helpful info guys! Problem not solved yet but it certainly did help.

Okay, so both fans did come on when grounding A to B. Radiator is clean. Started engine and no fans came on but when started with the AC, both fans kicked in - is that normal? Maybe it's alright. Could it be a bad thermostat? Going to change it anyways as preventive maintenance.

Also checked voltages and connections and everything checked out: 5 volts to the temperature sensor and ground is good.

Once again, thanks!!

... and once again, kind of need my car so hurry back and answer!

 

Your fans are running as designed, they come on at 228 F, when the a/c is turned on, and when forced on by jumping the two pins on the test terminals. At 250 F they had better be on or something isn't right.

 

jfb is correct. One thing to remember though. When the temps come up the lower fan on the right will not come on unless the A/C is on. The upper fan on the left is controlled by engine temp and the lower fan by the A/C. There is a mod done by a lot of owners who jumper the 2 relays together to get both fans on at the same time. This does help with the cooling. Now if you want to check the thermostat you can put in a pan of water on the stove, wife permitting, (I usually have to send her to the Hairdresser when I do this) with a cooking thermometer and watch to see what temp the stat opens at. This will tell if it is working and what temp it is.

 

How'd you bleed air from the system? If you saw a low coolant light and higher that normal coolant temperatures, I'd suspect the coolant being low and/or air in the system.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!

 

Alright, thanks guys! I'm hoping that the problem is solved... and of course, it seems to have been along my dad's initial thought of what was wrong. If not, I'll be back with more questions at some point.

Pulled the thermostat out - it was warped and stuck. Replaced it. Let the car run for awhile, tried to get it to heat up but couldn't get it hot enough to where the fans would kick on anyways so time will tell.

My dad's theory: knocking on the thermostat housing while it was hot was enough to knock it loose long enough for me to get home. Thermostat was probably warped from last week's overheating/leaking coolant issue.