My 86 IROC 305 TPI has consistently ran at 260 in the red in traffic, and the single fan has never kicked on sooner than in the red on the gauge. Although my car has never puked coolant or shuddered or ran bad in this condition I still do not like seeing the temp that high. I just changed the thermostat and radiator this weekend, hope it helps, but not sure yet. What is normal for my car to run at in traffic? 220? less? Is my sending unit for the gauge bad?

Thanks

 

The stock G.M. guages are notorious for being inaccurate. On the R.S. I had, the guage would read 220*, but when I removed the radiator cap, it wasn't boiling! At the time I had just bought the car, and it had no antifreeze in the cooling system either. Get the engine temp hot, and "crack" your radiator cap. Don't remove it all the way until you know there isn't any pressure there. If you are seeing a temperature above 220* on the guage, but it doesn't boil over with the cap loose, the guage is reading high.
It is most likely a bad sender.

 

I really have to ask if this is considered to be a safe troubleshooting method. The last time I attempted to open a radiator cap after the car was running, it blew the top off and radiator fluid came flying out. It somehow managed to miss me. I don't know if I would recommend this without prior warning first. Some people may not be aware of the potential dangerous outcome. Just a thought. Not saying don't do it, I am just saying be aware of the possible outcome.

 

Get a cap with the pressure release lever on it. Solves that problem. Last time I did it the cooland DIDN't miss me, so I ran right out and got one of these caps, no problems since, 'cept for the scars from the burns. This is why a lot of beer and working on the car don't mix

 

260* is cookin. Fix your problem. These cars were designed to run warm.

The fan won't turn on till 220* stock, so I would check your connections or like said make sure the temp gauge is accurate.

 

Ok, here is what I have come up with: I have an Actron Scan Tool that I used to check my temp on my car vs the dash gauge, when I'm showing pegged out 260 in the red on the dash, the scan tool (computer) is telling me it is really 225, and this is when my fan kicks on. The fan kicks back off at 215 (still isn't right is it?) I have a 195 thermostat in the engine and the gauge reads just a CH below 220 when the scan tool says it is 195. So I think I have a variable discrepancy in the reading as the needle travels up the gauge. So which is it the sensor, or the gauge I should replace. I truly trust my dash gauges to tell the truth, should I maybe replace the factory set with a high quality aftermarket set? Are there any that fit the factory locations?

Thanks
Brent

 

Your fan cut-in and cut-out points are about right, except that the fan normally turns on at about 230°. But your scan tool is reading the temp at the top of the intake manifold, and the temp gauge sender is reading the temp of the head, and the 2 places aren't necessarily at the same temp.

Your car is not overheating, it's running exactly as it did from the factory. That might be hotter than you would like, but that's different from "overheating".

Change the gauge sending unit. It's less than $10, and it's very quick and easy to replace, except for having to drain the coolant. It's in the left head between the #1 and #3 spark plugs.

Factory gauges are not accurate, ever. They are not instruments in the proper sense of the word. They are a trim package, not test equipment. Do not trust them or expect them to read accurately.

AFAIK there are no aftermarket gauges that will even remotely come close to mounting in the factory location. Take the dash apart and look, you'll see what I mean.

 

RB is correct. It probably isn't the gauge, but the sending unit. You can verify that with an ohmmeter by testing the sensor resistance at a known temperature. If the readings are different, it could be a failing sending unit of excessive corrosion and scale in the heads, insulating the sensing element.




And the fan setpoints vary a little depending on the PROM. The stock '86 TPI PROM was probably at around 230°F, but the factory upgrade PROM (AUM) has a 223°F cut-in and 210°F off. Various years had different temperatures, but they were all close to the 225-233°F area.

 

Ok I feel a little better, I'll just change the sender this week/end I just hope it comes out easy. I have another question, a freind of mine has an 86 IROC also, same engine and options, but he has some plastic duct work/dividers under his aircleaner assembly directing air to the air cleaners, I've seen pics of this setup in a Mitchell book also but mine does not have this, I know it is factory though, not a ram air system. I just have the vertical air dam under the radiator. Does theis aid in directing air to the radiator, or just air cleaners? I was just wondering because mine is all open behind the bumper cover.

Thanks

 

If you're talking about the lower air deflector that is mounted to the lower edge of the radiator support, you need to have one installed or you can lose cooling effectiveness in traffic (over 40 MPH). This deflector, or air dam, should be about 3" wide (tall?) and made of black ABS plastic.

 

Coolant in are cars start to boil at 220? If its boiling in the radiator, would it be boiling in the overflow tank too?

 

260? holy christ i never run above 180 course i dont take it out on 95 degree days

 

I made my own fan switch so I can turn them on so the car don't get any higher in temp than I want it to

 

I have heard that a 50/50 mix of antifreeze and water at 15 psi will not boil over until about 260 degrees.

 

Who cares, 260* and you're going to risk engine damage.
Here's a pic of the air dam, I just caught Vader mentioning, I didn't read every post.

 

I stated earlier I have the air dam, I put a new one on last year. But isn't there supposed to be some sort of duct work/divider behind the bumper cover(driving lights) infront of the radiator/ac condensor, splitting the air path between the air filters and at the same time direct the air that the air dam pushes up help push it through the radiator? I wish I had a pic. I know I have you guys confused because of the air dam responses you have given, but that is not what I am talking about.

 

Well, that's not entirely true.

As they come from the factory, most of these gauges aren't calibrated very well. The coolant temp gauge seems to be the worst offender because of its non-linear scale, while the tachometers are usually better.

However, I've had two tachometers that were dead accurate between 1000rpm and 6000rpm, and a third that I adjusted to be that accurate simply by moving the needle. At least, they were accurate to the limit of the resolution of the gauge and the needle--if you're going to tell me you can read the difference between 5775 rpm and 5600rpm, you must have better eyes than I do.

Many of the other gauges I've found can be calibrated the same way, since the values are known. The fuel gauge is one, since we know it is 90Ù full and 0Ù empty. The gauge is linear, so 1/2 full must be 45Ù, and 1/4 and 3/4 must therefore be 22.5Ù and 67.5Ù, respectively. By adjusting the needle, I was able to make at least one of my fuel gauges very accurate (to be honest, 90Ù was one needle width above F and 0Ù was one needle width below E). I've done this with the voltage gauge and the oil pressure gauge as well. I had one set of gauges from an 88 IROC that were calibrated and completely accurate for everything except the temp sensor, and even that was accurate between the 1/4 and 3/4 mark.

Of course, some of the gauges are simply off, and I had to go through a few to get the accurate ones. But to say the factory gauges can't ever be made accurate is misleading.

 

I'm trying to change the temp sender right now, and it won't budge! I just sprayed some PB Blaster on it and decided to ask the 'experts' how to get this thing out while I wait. When I try wrenching on it I have visions of it sheering off How durable are these things, can I really put the torque to it?

 

I love PB Blaster, the sender broke free right after I posted that last message. Still though same result, fan doesn't kick on until past 260 (according to the gauge)!! So I took an Ohm reading from the sender in the head (gauge sender), 163 Ohms, and looked it up on Vader's table (thanks Vader!) and 163 Ohms falls somewhere between 210 and 220 on the chart. So I again hooked up my scan tool and checked what the computer perceived the temp to be, it came back as 206. I think I have a very badly calibrated gauge. Now how exactly did you move those gauge needles, 99Hawk120? If I do that and it still isn't accurate I guess I'll go hunting for a new factory gauge.

Thanks for all who helped me sort this out.

 

Try this for the factory locations

 

Man my temp gauge is off too. Its weird, I keep reading all these different posts with people having a lot of the same problems as me. STOP HAVING PROBLEMS PEOPLE SO I CAN HAPPILY IGNORE MINE!

 

That is one sweet looking dash, DM91RS Did you make the gauge panel yourself? Or can I buy one, and put in the guages? And how do you wire it all up?

 

It's pretty simple actually.

Get the car up to a steady temp and read the temperature from the scan tool.

Carefully pry the needle off (and I do mean carefully, they are easy to break!), and then put the needle back on pointing at the temp indicated by your scan tool. It may take you a couple tries, it always does for me. Then shut the car off, and come back later (after it's cool), start it back up, and compare the gauge to the scan tool as it warms up.

To be honest with you though, it sound like the gauge has gone bad. But it doesn't hurt to try calibrating it.

 

I think your right, I repositioned the needle to 225 according to the scan tool (also when the fans kicked on) and now when the engine is cold the needle is pointing at the 5 o'clock position, and operating temp is now between 100 and the first notch past. I guess I'll change the gauge, or go for a set of aftermarket gauges like DM91RS's set up.

 

Yep, it's definitely bad then. Too bad you have an 86, because I've got an 84 temp gauge around here that I know works halfway decent.

 

It's not mine....I just had it on file and will be trying to remember where I found it for you guy's.

This is mine......

 

Found it

http://www.geocities.com/jbenge/dash_project.html