My 92 Z has 34,000 original miles on it. I have had a problem with it not getting warm(above 110 degrees) while driving. The car doesnt want to idle while cold and wants to die while coming to a stop unless I 2 foot it.

If the car is sitting idling, the temp will go up to over 220 over a period of time and continue to climb. That is until I start to drive, then the temp goes back down to a little over 100 degrees. I have replaced the T stat, changed the coolant, bled the system of air. Looked for vacuum line leaks, checked fuel pressure etc for the idle problem. I found nothing, Im sure the car not getting to temp and staying there is most of the problem.


Any help would be great.

 

no one knows?

 

Sure sounds like the thermostat is open all the time.

If you leave the radiator cap off w/ the engine cold and start it, does coolant start flowing immediately or only after the engine warms up a bit and the thermostat starts to open? If the thermostat is open all the time (stuck) or the engine doesn't have one, the radiator will dissipate a lot of heat when you start driving and air is moving through it. Otherwise, the temperature will continue to rise (just as you described) until the fans kick on and pull air through the radiator.

Does the car still have a heater control valve? The valve that prevents coolant from flowing through the heater core until the heater controls call for heat. If that valve is bypassed or stuck open, depending on how the system is plumbed it may cause coolant to flow through the radiator all the time causing the same condition.

 

The T state is opening and closing like it should. I removed a 160 from the car and replaced it with a 195.

Yes the car still has the heat control valve, teh system hasnt been touch since the factory installed it.

 

do you have electric fans?

 

You should hook up a mechanical temp guage and make sure thats actually whats going on, and its not just a failing sensor or temp guage. The guage in my '83 failed, and it read way hot at normal running temp, and way cold at slightly below that (like maybe 10-15* less, like when you're moving).

 

Yes the car has the stock electric fans. The sensor is fine. For instance, I let the car sit at idle today until it reach 160 degrees,the car idled fine when coming to a stop etc, as the idle normally jumps all over and wants to die.

As soon as I started drving the temp went back down to 110 and teh car started surging, and idling from 1000 to 1500 to 800 back and forth.

 

I almost wonder if you have a slightly leaking head gasket. Just a thought, don't want to alarm you.

Reason I say that, is because that has also happened to me. The head gasket was not blown, but had a slight leak into one cylinder. When the engine would sit, it would leak in a very small amount of coolant into that cylinder, but not enough to hurt anything or get any into the oil.

BUT - it made the cooling system and temp guage do some really funky weird things... One being some really erratic readings on the temp guage because of compression being forced from that cylinder into the cooling system in the form of a hot air bubble. When this happened, the temp guage would quickly climb to about 230*, then stay there for a bit, then drop right back down to about 180-190*. Changing the guage sender or the thermostat didn't help at all.

Was never bad enough to cause any running problems though. But over a week or so, you'd have to add to the coolant level... maybe a liter or two over a week. It wasn't leaking externally.

 

Im not missing any coolant, the overflow tank stays at the same level when hot and cold. Im thinking it could be the tune thats prgrammed into the E Prom.

 

Something has to be changing to cause the problem. What's the timing doing while this is happening? Same question for the EGR and IAC valves.

If those seem to be operating normally, check the TPS and CTS outputs.

 

The timing stays the same. The EGR was just recently replaced in July. The TPS is working like it should

 

Bump...

 

My car is doing similar things. I did previously have a 160 thermostat, but now that its winter it wasn't getting warm. So I got a 180 stat from Autozone and it worked great for about 4weeks, now its stuck open and my car temp doesn't go higher than 100-110degrees driving and takes its time to warm up at stop lights (if I'm stopped long enough). So I'm replacing it with a 195 stat soon. Its a dumb question, but do you have the correct t-stat? There isn't a possibility that coolant is going around it? As long as you don't have Mr.Gasket...

 

Same thing here as well. Must be the time of year we need heat or something. I have done 3 new stats and all the same. I get to temp fine and hold fine, but the minute o go down the road she cools off to about 130-140 and holds till i stop again. Sucks with no heat.

The only thing i can find is that the heater control valve must be letting coolant flow from the intake to the heater core and around the oil cooler and back to the radiator. This must be enough flow to drop the engine temp even with a fully closed stat. I should go get a new control valve snd try it. Does one port on the valve always stay open? If so how would a bad valve even matter, as coolant will either flow to the heater core or just around it. It would still bypass the stat.

 

I believe the basic purpose of the heater control valve is to prevent coolant from flowing through the heater core when it's not needed. So, the answer to your question is: Yes, there will always be coolant flowing through two of the ports, but not all three at the same time.

If I recall correctly when I flushed my system and replaced the coolant right before storing my car, coolant will flow through the heater core when there's no vacuum to the valve.

I've often wondered what the benefit is of the thing - increase life of the heater core, improve A/C performance, shorten engine warm up, etc.?

In case you're interested, there's threads or tech articles on this site for relocating or even eliminating the heater control valve. Other than improving the looks of the engine compartment, I don't know of the pros & cons of eliminating it.

 

That is how i see it as well, and mine is working that way. All the valve does is allow or block the heater core loop only.

How GM designed this it looks as if the intake outlet (bypass stat) can flow enough and return it to the radiator that the stat can stay closed. Older cars plumped this return line to the plugged inlet side on the top of the water pump and didn't dump it to the radiator. So the fluid never was exchanged for cool water but only back into hot water. I don't see how these worked right form the factory. What am i missing? This is a 5/8 line to bypass the stat basically. How can this be right?

 

I think it's still a similar setup when coolant is flowing through the heater core - only a bit more confusing.

Instead of returning to the top of the water pump like the old configuration, coolant is sent to the 'cold' radiator tank. But, this coolant doesn't go through the radiator core (to dissipate heat), it goes directly to the water pump inlet and back through the engine block.

 

My T stat is the right style for the car. I have tried 2 different new ones, A high dollar end one that I found in my garage, and 1 from Oreily's. The car still wanted to overheat while idling, and wouldnt go above 115 or so while driving.

Now The car doesnt get a little bit over 100. There has to be soemthing with it. It shouldnt overheat while idling, and get that cool while driving.

 

Have you checked the CTS? I'm not positive, but I believe there are two temperature sensors. One for the gauge and another for the ECU. The one next to the thermostat is the CTS for the ECU.

 

No I havent checked that sensor. I'll have to do that once it warms up, I cant stand to be outside more than a minute or so.

 

Look up the resistance/temp specifications for your CTS thne remove it read the resistance as you cool/heat it, or simply replace it.


There's a possibility that the eprom was reprogrmmed for the proper fan on/off temps so changing back to a 195 will cause problems.

 

I went back & reread your original post. The two problems you're fighting may need to be addressed independently. The more important of the two being the engine coolant temperature.

The coolant temp is controlled by the thermostat, fan(s), and the ability of the radiator to dissipate the heat. Since you've already changed the thermostat and the radiator obviously dissipates enough heat while driving, the only things left are the fan(s) and the water pump's ability to generate enough flow at idle. Are the fans kicking in at or before 220 degF? If not, again the CTS is the device the ECU uses to determine coolant temp in order to control the fan(s). Two more things, the radiator cap & coolant itself. I'm assuming you're not using plain water as coolant - at least not w/o a wetting agent. What condition is the radiator cap in? I don't know what effect system pressure has on flow. But, I know it's needed to prevent the coolant from boiling and possibly causing cavitation & vapor lock at higher operating temperatures.

Now for the heater issue - with all heater controls in the off or cold position and the engine idling & approaching 220 degF, feel for the presence of heat in each of the hoses connected to the heater control valve. One of them should be cooler than the other two - the one leading to the heater core. When the heater controls are moved to the heat / hot position, that once cool hose should get as warm as the other two very quickly. If it doesn't either the valve isn't diverting the flow of coolant (try disconnecting the vacuum line, too) or there's something blocking the flow. It could be a plugged heater hose/core or vapor lock. Sometimes, vapor lock can be solved by simply revving the engine a couple times. If that doesn't get the flow going, see if you get any flow through the heater core by isolating it from the rest of the system and using a garden hose. If you get a good flow through the core, the heating problem might be related to air flow through the heater core. Does the heater fan run and are you getting any air through the vents? If not, there may be a blockage from debris or a little varmint making a nest in the venting somewhere.

 

Drop $60 for an ALDL cable, or make one up for $10.

Beg/borrow/steal a laptop and read what the ECU sees from the CTS for temperature. If you don't get a good feeling, replace the CTS. It should be pretty obvious.

Once you have done that, THEN you can compare to the gauge. If the ECU temp and the gauge temp are different, replace the temperature sending unit and or/gauge.

Right now, you think you have temperature issues, but you are basing it on the gauge, which along with its sending unit, are known to be unreliable.

 

I am using a 50/50 of antifreeze. The rad cap is brand new. All the vents have air being pushed out of them. Thats the other problem I have noticed. Here by me its been about 20 degrees and cooler at night. The car doesnt get any warmer than 110. It can idle all day long and the temp wont budge. The heat inside the car on full blast and on the warmest setting should blast me out to crack a window. It doesnt, it gets warm but isnt what it should be. I would say 78 degrees maybe?

Im think the tune in the E Prom has something to do with it. The car has a aftermarket eprom that wa tuned for the engine work before I bought it. I also have no clue whan the fans turn on or if one fan turns on since I dont have A/C anymore.

 

I'm at a loss for any new suggestions. But, I'm also baffled ... in the orignal post you stated "..If the car is sitting idling, the temp will go up to over 220 over a period of time and continue to climb.." which is why you would want to check when the fans are being turned on and the CTS.

When I replaced my CTS, the bad one read ~10K ohm @ 75 degF and ~30K @ 180 degF or so. The replacement read ~3K ohms @ 75 degF and ~200 ohms @ 180 and was around $20.

 

Now with the cold the temp will not move over 110. The only time the temp rises to 220 or over is when its warm outside say 50 and up.

 

If you don't know what has been modified in the EPROM I would suggest running a stock chip until you get this resolved, but that may be easier said than done. Data logging might be easier if you can find someone who has the equipment, that would show when the ECM commands the fan to turn on among other useful data.

For now I would look into the fan situation.
As was said the primary fan should turn on somewhere above 200°F, but nothing has been posted about it turning on at all. One way you can test it is by jumping the ALDL diagnostic port A&B pins ECM will test the fan (among other things.) The secondary fan can be tested by disconnecting and grounding the temp switch connector on the passenger side of the engine.

 

Either coolant is bypassing the thermostat and getting to the radiator or it's so cold the engine isn't generating enough heat to overcome radiant losses. You might try a block and/or oil heater in this colder weather.

 

When I bought the car, the old owner did state the the car doesnt like cold starts. Even when it is warm outside you have to give the car gas to start up immediatly. Otherwise just cranking on it, takes a few seconds (5) for it to start, and then the idle will fluctuate.

It almost acts like its carbuerated and the choke doesnt open.

If I run the stock chip, wont that make the idle problem (surging) etc even worse? This what is done to the car.

TPIS Big mouth Intake
TPIS runners
TPIS plenum
ZZ9 Camshaft
GM performance 1.5 rockers
Springs,pushrods,locks,Comp cams Rocker studs
MSD distributor, 6 AL Box
Cloyes double roller timing chain set
TPIS throttle Body
So called Re programmed E prom, I have the stock one.
24# injectors
Hooker haeders
Borla catback


I would think that the car with another E prom programmed for the ecaxt mods would have the car act, run Idle like it would stock. Meaning no surging, etc. If the E prom doesnt have the exact specs preogrammed into it, couldnt that possibly cause what Im experiencing?