Over-Heating '92 Lumina z34

[Alan_m]

I bought a '92 z34 last week that needed an alternator. Drove it home on the battery and it didnt over-heat at all. It would heat up to about the 3/4 mark and back down to the 1/4 mark and didnt seem like it was holding pressure in the upper rad hose. Seemed to me that there was no tstat or it was stuck open. So after I changed the alternator, all seemed well until I broke the golden rule of "If it ain't broke don't fix it!"

So i changed the tstat to a 180 to replace the 195 that was in it. I bled the system at the valves located on the tstat housing and the heater hose and the temps looked fine while idling. On my way to work the next day i drove about 12 miles and it started to overheat, hit the first red-line, about the same time I pulled in the parking lot so I shut it down until that afternoon. on the way back from work I drove about 5 miles on the highway and it started to get hot , first red line and the dummy light came on so I pulled it over to hopefully prevent any damage. 2 minutes later I startedit up and it drove fine the rest of the way to work without over heating. Today I wasnt so luck, I made it about the same distance pulled off to the road sat about 5 minutes the temps were around 1/4 mark then back to almost red within about 2 miles down the road. pulled over again...pretty much limped it home..bled the cooling system again. Let it idle and it was getting to hot idling so I shut it down. I also noticed that the coolant in the res doesnt change levels at all. I actually over filled it to see if it would drain or over flow and it just sat there. the rad is full of coolant and I just replaced the rad cap this morning and the upper line seems like its holding pressure so does anyone have an idea what is wrong I dont know a lot about mechanics so any help would be appreciated.

[pocket-rocket]

If the radiator cap is original you might want to replace it.

Over time they get weak and the release pressure gets lower and lower. The reason for the pressure in the first place is water boils at higher temps at higher pressure, so if you bleed the pressure off (bad cap) the boiling point is lower than what it could be, and steam won't cool your engine like coolant will.

Hope this helps, and welcome to the forums

[Alan_m]

just changed the cap this morning ... Im thinking its the water pump? Also is the water pump as bad as the alternator to change or worse lol? I was thinking about just changing it since I can get a new one for like 20 bucks.

[Schurkey]

How about some actual diagnosis before you start flinging parts at it?

Do the fans work? Both of them?

Does the system re-fill with "air" after bleeding? Defective head gaskets will allow coolant into the cylinders, and combustion gas into the cooling system. Neither is good.

Is the engine actually getting too hot, or is your temp gauge/sensor faulty?

[Alan_m]

How about some actual diagnosis before you start flinging parts at it?

Do the fans work? Both of them?

Does the system re-fill with "air" after bleeding? Defective head gaskets will allow coolant into the cylinders, and combustion gas into the cooling system. Neither is good.

Is the engine actually getting too hot, or is your temp gauge/sensor faulty?

I havent noticed any air after bleeding this last time. I can only ever get one fan to kick on and I think it runs constanly, the other Ive never seen on, I think i read if you turn on the ac the second fan will turn on but I havent gotten it too. I dont have any equipment to test the actually engine temps.

[caffeine]

I would think if it was overheating the second fan would turn on. You could test if the fan works by jumping two terminals in the relay.

[pocket-rocket]

I would think if it was overheating the second fan would turn on. You could test if the fan works by jumping two terminals in the relay.

The fans also turn on when you jump the diagnostic port terminals to pull codes.

If your water pump were bad it would most likely be weeping coolant and the overheating would be a little more consistent, I would think.

Sent from my HTC One X using Tapatalk 2

[Alan_m]

Last night I let the car idle in the drive for about 40 minutes. The temp would get to 1/2 then drop to 1/4 this happened several times, so I decided to drive it. Drove about a mile and it overheated. SO I got back to the house let it cool a bit then uncapped the radiator and let it run for a few minutes. I revved the motor just to get it flowing and it looks like there's some corrosion in the system, I noticed some trash in the coolant that purged also it started looking more brown than green at times. Guess I'll flush it this afternoon and see if that fixes anything. Thanks for the help by the way and ill look at the fan situation too.

[Syndicated]

This same thing happened with my jimmy, right after I changed the head gasket and intake gasket.
Turned out my new thermostat was bad, after changing the rad cap and thermostatic fan clutch.
The motor would act like the stat was stuck open while warming up, as soon as it hit 180, the temp would sky rocket to max with 2 mins.

Bad batch of Chinese thermostats maybe?

[robertisaar]

IIRC, only fan 1(driver's side) will come on during a code pull.

but even if neither fan worked, there should be more than enough airflow on the highway to keep it out of any dangerous area.

since this all happened after changing the thermostat, Syndicated's suggestion doesn't seem that improbable.

[Alan_m]

Ok what would be the next step? Should I Remove the thermostat and see how it runs without one at all and if it still overheats flush it? if it does run better without it should I get another 180 or a 195? I do still have the original 195 I replaced as well...

BTW this is the tstat I put in there, dunno if anyone has an opinion on the quality, just wondering if these are notoriously crappy tstats or something..

http://www.oreillyauto.com/site/c/detail/MCS0/3898/03442.oap?year=1992&make=Chevrolet&model=Lumina&vi=1053942&ck=Search_thermostat_03442_1053942_730&keyword=thermostat&pt=03442&ppt=C0331

[Schurkey]

Ok what would be the next step? Should I Remove the thermostat and see how it runs without one at all and if it still overheats flush it? if it does run better without it should I get another 180 or a 195? I do still have the original 195 I replaced as well...

Don't bother to run without a 'stat.

Either re-install the original 195, or put in a new 195. A 180 is not right for this vehicle.

How old is the coolant? Probably due for a flush anyway? If it's older than five years, you're probably due. If it's not older than five years, you might be due. If it's less than two years old, you're not due for a flush unless it's been contaminated somehow.

Can you see corrosion in the radiator through the rad cap opening? Have access to a borescope or videoscope?

[Alan_m]

Actually I have no idea how old the coolant is, I think the car was setting in someones yard for about 6 months or more before I bought it. I think ill flush it today. Any recommendations on a good flush solution?

[Schurkey]

DRAIN the coolant first, using the radiator AND the block drain plugs. Around here, we're supposed to flush the coolant down the toilet or dump it into the sink to be processed at the wastewater plant. Other places accept coolant for recycling. The LAST thing you want to do is to dump it on the ground, or into a storm sewer.

After you've drained the coolant, flush with water. I've been using Prestone flush tees connected to the garden hose.

http://www.amazon.com/Prestone-AF-KIT-Flush-Fill-Kit/dp/B000CCFY5W/ref=sr_1_1?ie=UTF8&qid=1360796051&sr=8-1&keywords=Flush+Prestone

I tend to run the engine after flushing for a few minutes, with the engine running--and revving at 2000--3000 rpm, the water pump helps to scour the cooling system.

Drain the water using the radiator AND the block drains, and then install anti-freeze BEFORE adding pure water (reverse osmosis or distilled) DO NOT buy "pre-mixed" anti-freeze/water coolant mix.

[Alan_m]

just picked up that prestone flush and fill kit and flush chem at the local parts store, thanks! I have resealable 5 gallon buckets I put my fluids in for recycling so Im set there. I will preceed with the flush after work tomorrow, had to work late and it got dark outside, so heres the dumb question...lol where are the drain plugs located on the block? i'll keep you posted on the progress.