Over-Heating '92 Lumina z34

[Schurkey]

where are the drain plugs located on the block?

My '93 3.4 DOHC has a drain plug (steel pipe-thread plug with a hex-head) on the firewall side of the engine, low and towards the transmission bellhousing. As I recall, it takes a 9/16 socket. It's a pain in the ass to get at, since it's tucked behind the exhaust downpipe and to the left. You'll have to get at it from underneath.

The front/radiator side of the engine has hoses for the oil cooler, so I just drop a hose to drain the forward engine bank. A 3.1 probably has a plug similar to the back side of the engine, rather than the oil cooler hoses, and this would be near the oil filter.

I tend to replace steel pipe-thread plugs with brass pipe thread plugs; or better still--brass draincocks. I use Loctite/Permatex PST #565, #567, or #592 for thread sealer, but any pipe thread sealer will work.

The draincock in the radiator needs no sealer, thread it out to drain, thread it in to seal.

[Alan_m]

I have the 3.4 DOHC in this '92 as well so I'm defiantly going to follow your lead here, i actually feel more confident now talking to someone about this motor that knows their way around it. When I told my friends I bought a car with the 3.4 DOHC one said, "That’s a pain in the ass under the hood" lol

[Alan_m]

Ok I flushed the system, now when I run the car I get a "service engine" light after driving for a few minutes. The car still overheats with the thermostat, but I can take the thermostat out and it doesn't overheat, but will rise to about a 1/4.

[Schurkey]

Ok I flushed the system, now when I run the car I get a "service engine" light after driving for a few minutes.

What codes? What does the scan tool show for coolant temperature, fuel trim, IAC position, etc?

The car still overheats with the thermostat, but I can take the thermostat out and it doesn't overheat, but will rise to about a 1/4.

Wrong thermostat? Defective thermostat? Does it open if placed in a pan of water on the stove--use a cooking thermometer to see when it opens, and if it opens smoothly and fully as temp goes up. Should be fully open 15--20 degrees F. above the 'stat rating. 195 thermostat opens at 195, should be fully open at 215.

[Alan_m]

What codes? What does the scan tool show for coolant temperature, fuel trim, IAC position, etc?

Going to see if I can find someone to pull the codes today since I dont own a diag tool.

Wrong thermostat? Defective thermostat? Does it open if placed in a pan of water on the stove--use a cooking thermometer to see when it opens, and if it opens smoothly and fully as temp goes up. Should be fully open 15--20 degrees F. above the 'stat rating. 195 thermostat opens at 195, should be fully open at 215.

Yes I placed the new tstat in a pan of boiling water and it fully opened, ill use a thermometer to check the water temp.

[Alan_m]

Ok I figured out the problem...I had a total "Duhr" moment. I had the belt routed the worng way and the water pump was turning backwards..geez I feel like a dumb ass! But there is another issue..I found out that the secondary fan is being jumped in the relay box to run continously when the key is turned. The primary fan never turns on. The "low coolant light" is on and the fans wont turn on(with relays in and engine at operating temp) without jumping the relays. Im thinking the ECT Sensor since the relays are being ignored?

[TGP37]

EDIT: Backward belt, lol. I guess I should've checked for a solution before posting. Either way, good advise below.


I just mentioned this in another thread.

The line between the rad cap and the overfill is important and all too often over looked.

Any crack around the fittings will allow coolant to slowly dribble out when warming up. Once fully warm it won't leak, usually.

Once the car cools down the contracting coolant places a vacuum on the over flow tank and pulls coolant back in. If there is a crack, air is drawn back instead.


The air can be pressurized which allows the coolant to boil over at a lower temp. The steam pockets prevent proper coolant flow.


Seal the overflow line, I bet that is the problem.