Overheating at idle 90% of time

I have a 92 Transport with 189,000 miles. Just did radiator flush an' fill and replaced thermostat. On hot days while idling, the temp gauge will go to the last yellow line before the red. I know the fan comes on because I have checked it. When I get back on the highway, it will run around 200 or so. IF it is cool outside, no problem. What should I do?

First make sure the fan is spinning with enough force and it stays on. Then check the circulation. Your water pump may be getting weak and needs replacement.

First make sure the fan is spinning with enough force and it stays on. Then check the circulation. Your water pump may be getting weak and needs replacement.


Exactly how do I check the circulation???

Depends how it looks like. I normally have the radiator cap open and let the vehicle warm up. Once it's warm (thermostat is open) you should be able to see the water circulate and circulate faster when you give it gas. If you don't see it circulate, or circulates on and off, then your pump is going bad.

How old is the rad in this van? Could be galleries clogged and flush will not clean it out. Might be time for new rad.

But it only "overheats" at idle at high outdoor temps, like over 85 f. It runs at 200-210 degrees at highway speeds in hot outside weather. It has had a rad replacement at least once in the last 6 years.

In 40 years + of mechanics, I've never seen a pump failure other that when it started leaking fluid out through the bearing, or bearing failure accompanied with horrendous noise. I've never seen a car pump impeller damaged in a way that water circulation would be compromized.. AM I really lucky? However, I've seen numerous water circulation thermostats that would block in the closed or partially closed position, clogged radiators even when they do not seem to be clogged, and thermostat switch that would not switch the electric fan on - but on the transport (mine is 3.8 '93), it is controlled through the ECM.

So once you have cured your overheating problem, please tell me so I adjust my statistics.
Bye

In fact, if I had your problem, I'd try first removing the thermostat. Cost nothing, and results show fast. If problem resolves, then install new thermostat.

LMP,

It is not the thermostat. I replaced it and still same results. Did you notice that it is intermittment? My fan comes on at 230 according to my dash gauge. ANy other suggestions?

Since it is intermittent, I would think it's the fan. You say it does turn on but you need to check when it overheats to see if it stays on. And I have replaced water pumps even though it was not leaking. And that was the problem.

Where is the switch that controls the fan coming on at 230 degrees?

No switch: the fan is controlled through a relay directly from the computer (known as Powertrain COntrol Module (PCM) with 3.8, Electronic control module ECM with 3.1) that reads the temperature from the coolant temperature sensor. So it is the computer's decision that turns the fan on. There is one single coolant temperature sensor that serves the gauge directly and also feeds information to the computer.
NOw the relay itself may be the culprit: in fact there are 2: one for pusher fan , one for puller fan. They are located RH side of engine compartment, behind composite headlamp.

LMP,

I believe I have a problem with the puller fan. As a matter of fact, I didn't know I had one 'til today. I got it up to temp (200 or so) then let it idle with the a/c on. the pusher fan ran. I then turned the AC off and in about 30 seconds or so, the pusher fan shut off. I kept it idling until the temp got to 230 and the ac fan came on again. The puller fan never came on. Now what?

LMP,

I went looking and I can't seem to find the relay.

There are several relays - 4 in fact, - located behind framework behind composite headlamp (passenger side).
Counting from radiator toward the passenger side fender, there are:
-a/c compressor relay
-coolant puller fan relay
-fuel pump relay
-coolant pusher fan relay
-one more relay position that shows empty on my picture.

mmm...and they say relays may not be indexed on mounting rail in order shown...!! However, the first three in list above are fed by wires coming from a common bundle while the pusher fan wiring has a separate harness.


I may scan the picture I have here and send it to your e-mail.
(this is ,93 service manual but this is similar to 92)

I can check to see if any electricity is going to fan with my voltmeter. Do you know at what temp it's supposed to come on? I figure I can unplug it right there at the plastic frame thingy and see if it is getting any juice. If it is then I figure it must be the fan motor. Make sense?

Makes sense...I had just posted the picture at http://www.avigex.ca/relays.jpg

I have just posted the diagram for 3.8 at http://www.avigex.ca/fandiagram.jpg
If a 3.1, please tell.I'll post it

thanks!!! AFter paintball on Sat I'll check things out.

thanks for your help. It was the puller fan motor.

Glad you are through.
Regards
LMP

HELP!
Having the same issue with my 91 transport... changed thermostat- now they are telling me its the water pump and that in order to drive it i can't idle at anytime. how do i fix??? cant afford guess work... eeeek!
thnx

HELP!
Having the same issue with my 91 transport... changed thermostat- now they are telling me its the water pump and that in order to drive it i can't idle at anytime. how do i fix??? cant afford guess work... eeeek!
thnx

First go for the obvious: turn the A/C on, and BOTH fans will turn on instantly, so just check to see if they rotate. If the car runs normal on highway and overheats only at idle, then most probably you lack fan cooling .

I really doubt the water pump could be the problem, because on the highway, water has to circulate too and if it runs in normal temperature range in those conditions, then your water pump does its job.

Do what LMP says. PRobably you will see the fan BEHIND the radiator on the air cleaner side never runs. I got a motor for $60 new. It's really easy to replace. Make sure and unplug the connection and make sure you are getting juice to the motor, though. It could be a switch or some other connection.

when you switched your t-stat, did you follow the proper airbleed proceedure for the cooling system. If not, you could have air trapped in the engine. You must bleed the air out using the valves on the t-stat housing and transfer tube (near water pump) or the air may never purge itself. The ect controls your fan operation, so if there is air in the system, it may not me immersed in coolant, thereby not turning the fans on

YEp, sure did. THanks for info though.