I have a 91 z28 5.7 tpi and its over heating, ive replaced the water pump, coolant temperature sensor, radiator, thermostat, and it still overheats, the passenger side fan doesnt come on, and ive replaced that motor as well...could that one fan not running cause it to overheat? is it a bad relay? do i have a cracked block/head maybe? im so confused and tired of throwing money into parts that don't remedy this problem...ive also considered air in the coolant system...can anyone suggest anything? perty please? thanks!

 

Puddle underneath? Any smell of unexplained " sweet " in the car, exhaust, or under the hood?

Check the oil & see if ther is water in it.
Does the bottom rad hose collapse when you rev the motor?
How old // new is the rad cap? Is the overflow // recovery bottle
working? Is there an air dam under the car? It attaches right under the rad
& hangs down just a bit lower than the front GFX.

Sorry, can't help with the fans thing.

 

_

 

Is it over heating around town ? sounds like the high speed fan is not coming on.
First look at the basic things.
Need to look at replacing the fan switch autozone part number sw502 but have them double check it. You can also make the fans come on by turning on the ac and see if that helps.
Also check all the connections especially at the switches and make sure they are tight.
Has anyone messed with the timing at all. If so is that when the problem started ?
How hot does it get ? If you have access to a scope or good hand held scan tool that shows live data get it and see what the temp is compared to the gauge and see if it's signaling to turn on the fans. Out of the 2 highlited the air dam is the most important. With our cars GM actually that was 100% mandatory because of the small grill openings. If the cap is not new get a new non lever cap.
You might try taking the thermostat out and boiling it to verify its opening temp.
What temp therm. did you put back in ? and is there a perf. chip in the ecu ?

Now the not so basic stuff.
If you do get a hold of a good hand held scan tool take it for a test drive and check to make sure that it is reg. engine ping and retarding the timing, but remember that if the engine is getting really hot that will also make the engine knock. Kind of a catch 22 there. If the temp is fine and the engine does knock is the ecu sensing knock ? If it is it trying to retard the timing ? if so, but it can't you need to have the control module checked.

This is all a start, but should put you in the right direction.

 

yeah, the gauge shows it at over 220 around town and rises slowly until it reaches red, the timing was messed with by a gm shop...seams to be leaned out...so i would imagine that would cause it to run a little hotter than usual...I put a 190' thermostat back in..new pump, radiator...havent revved to check the bottom hose yet...my a/c isnt hooked up either, when i say that i mean all electrical is hooked up but the adapter for the free-on in the back is hanging loose, i wouldnt think that is a big deal..maybe im wrong...ooh! and the knock sensor wire came disconnected a while ago...is that telling my ecu to compensate for something if it isnt hooked up? all these sensors just confuse me...the wire was burned by my header a while back...havent gotten around to fixing it...and the air dam is going back on soon....but the air dam wouldnt help it not get hot at stand still before driving would it?...eeehhh anyways

 

Really sounds like the fans are not coming on at all. Even with the a/c compressor gone if you put the controls to ac it should still trigger the fan. With the knock sensor not hooked up it should be throwing codes. What's happening is the ecu doesn't know knock exists and is not retarding the timing so peformance, mileage and engine life are all being compromised. Engine knock can break off the top ring lands off the pistons if it's not taken care of.
No the air dam won't do anything at a stand still, but around town driving it will.
Get the knock sensor fixed, air dam back on and both fans working properly and your problems should be a thing of the past. Also make sure the timing is set by the book and right on 0. You can advance it a couple of degrees after the overheating is fixed.

 

You didnt say what temp the fan was coming on I have a 91 z with the 5.7 and my fan wouldnt kick on till around 275 degrees turned out to be the fan switch was broken the one between the back two plugs on the right side stock kicks on around 238 degrees put on in that comes on at 200 and a 180 thermostat . Hope this helps

 

i figured it out guys, thanks for all your suggestions!!!