Question : Overheating at stop

[Rabbi]

My 1992 lumina z34 with the 3.4 dohc in it has been having this problem for quite some time.

The car runs great, Doesnt overheat when driving down the road. Until you hit a stoplight or a stopsign.

Any long periods of sitting idle the car will begin to overheat and sometimes stall out.

The temp gauge does work, So im assuming the fans are just not cutting in. Is there some kind of sensor that tells the fans when to turn on?

Im going to replace my "Coolant Temperature Sensor" this week. Is there any other sensors i should replace while im at it?

Thanks

[Incydowt]

First off Iwould remove water pump and make sure it has the correct impeller, usually only the remans have this, otherwise you get a completely different impeller and it causes chaos with yor cooling system, I would also replace the coolant temp sensor as this is the switching device for the fans.

[RedZMonte]

there are 2 sensors.... one on the front cyl head below the dog bone mount, this one is for the guage only. the one on the back side of the lower intake manifold (drivers side) is kind of a pain to get to is what controls the fans, ecu, fueling ect..

1st verify that the fans are or are not coming on... could be a bad relay, blown fuse, short or a bad ground... IF they are not coming on i would start by jumping the power to the fans to manually turn them on to make sure the fan is not bad.. then follow it backwords... swap the relay, check the fuse ect... hope this helps. the car is fine when driving because the air is pushing threw the rad and cooling it down... IIRC the fans are not running at high speeds anyhow while driving.

[pocket-rocket]

IIRC the fans are not running at high speeds anyhow while driving.

True. I was told it is like this because they push less air than can flow through the radiator at speed and act more like a wall if on while up to speed. It's programmed into the ECM this way (not to turn on over a certain speed).

I also second Incydowt's comment on the water pump impeller. Remans have a junk stamped impeller. Some pushrod guys have gotten away with using them on pretty much stock builds, IIRC, but the DOHC produces more heat so we have to use a better flowing stock style impeller.

[Rabbi]

well i checked the radiator fans with a jumper wire and they do in fact turn on with 12v thrown at them.

But they will not come on by themselves when the motor gets hot or has been running for awhile.

any ideas?

[pocket-rocket]

Check to see if the fan relays have power and if the relays function correctly.

[jman093]

Check fuses too

[Rabbi]

well i went to pull codes today and did the "paperclip trick"

the fans turned on

this would mean the relay/fuses are infact good correct?

on a side note i ordered the rear 2 wire temp sensor, but really dreading doing this since its going to probably be a pain in the ass to do.
Hoping i can solve this without doing that replacement

[pocket-rocket]

well i went to pull codes today and did the "paperclip trick"

the fans turned on

this would mean the relay/fuses are infact good correct?

on a side note i ordered the rear 2 wire temp sensor, but really dreading doing this since its going to probably be a pain in the ass to do.
Hoping i can solve this without doing that replacement

Yes, your relays and fans are fine. The temp sensor IMHO is a good move.

[Rabbi]

arrg i was hoping that wasnt the problem
guess ill change that as soon as i get the time

[86FieroSEv6]

If you want to quick check the sensor circuit, you can disconnect the harness and jump the connector with a paper clip . . . . . . it should generate a coolant sensor circuit short code.

[velasaa2522]

hey guys im having the same problem with my LQ1 getting hot. It has a brand new thermostat, radiator cap, water pump, and coolant. but its still getting hot. what should i do? get a new radiator? the fans aren't coming on till the temp gauge gets in the red.

[pocket-rocket]

Welcome to the forums!

Did it start this before or after the new water pump? Also do you lose any coolant over time?

[velasaa2522]

yeah it has been getting hot for a few months now. i just put the new water pump in last week hoping that would stop the engine getting hot problem. but no difference. it does not leak any coolant. ive purged the coolant hose valves and everything.

[pocket-rocket]

The new water pump, did it have a stamped steel impeller or was it cast?

Cast:


Stamped:


If it's stamped, get that thing out of there and buy one with the cast impeller. As far as coolant circulation, the stamped can't keep up at stops like the cast can.