ronnie87iroc-z

I have a stock 87 iroc with 305 tpi. I changed the thermostat today with a new 195° and the sensor for the guage with a new gm sensor. Now my question is that is it normal for the guage to be at the first mark above 100° driving down the road? Sitting still it will get up to slightly above 220 but goes down to the mark between 220 and 100 when moving.

85-87IROC-LB9s

iTrader: (1)

Hello, welcome to Thirdgen.org,

First a couple questions. How is your cooling system in general? How are the radiator hoses? Are they cracked and are collapsing when the engine rpm's increase? How is your coolant? Does it have the proper 50/50 mix? How about the radiator and radiator cap? Is your water pump leaking at the weep hole? Are the seals on the radiator good and tanks un-cracked? Has your system been properly flushed? Finally, the most important, how is your fan harness wiring and relays?

The 1987 TPI setup is designed to turn on the primary fan either by the A/C or ECM by the CTS. This fan turns on @225 degrees F. The secondary fan, which is your fan on the right side, if your in the driver's seat looking out, is designed to be turned on by the fan switch (which is located on the right cylinder head between the no.6 and 8 sparkplugs). This secondary fan turns that fan on at 245 degrees F!

Make sure the you have the right psi radiator cap, and if you can borrow the radiator pressure tester you can test your cooling system for leaks. These cars, especially the TP cars were designed to run hot for emissions, but also decreases engine life. The gauges on these are a hit or miss. Some read correctly while others are off by about 20 degrees, depending on the sending unit installed (aftermarket or OEM). Also, take a look under your car to see if your air deflector is still in place, because that is one crucial element these cars need to cool the engine.

ronnie87iroc-z

No leaks anywhere. The fans work as they should . All hose look fine. Just wondering if what its doing is ok.

85-87IROC-LB9s

iTrader: (1)

For the most part, for it to be at the first mark while driving, that's ok. Sitting at a stop light and the gauge goes above the 220 degree mark, is pretty typical of the cooling system on the TPI. They are known to get that temperature. I would recommend putting a lower fan switch on the cylinder head (preferably hypertech's 200 degree switch), and having the member, TunedPerformance reprogram your memcal or make you a memcal to reprogram the ECM to turn on the primary fan at around 192F or 200F. In my opinion, and from my experience, anything over 220F is already too hot for me. The ideal temperature would be around 200-210F (in between the first mark and 220 mark) depending on your climate and driving habits. I have my car running at the first mark all the time, when I'm driving with my fan switch combination, and of course the radiator I have helps too. From the sounds of it your car seems to be running what is considered "normal" for a thirdgen TPI. Again, I'd recommend the lower fan settings.

ronnie87iroc-z

Ok good thats what I was needing to know thank you very much.

85-87IROC-LB9s

iTrader: (1)

One more thing, it sounds like your fan settings are operating as programmed. If the car gets slightly above the 220 degree mark, and goes down while driving, this means the fan is coming on at the programmed 225F setting. Meaning you have one fan working, because the other does not come on until 245F...

ronnie87iroc-z

Yes the fan on the driverside is working properly. Just seems weird that it runs that low but every other vehicle ive owned ran around the 210 mark most of the time. But at least I know the cooling system works great!