Last Lemming

Hard to tell with a turbo. There is so much stuff in the way you can't easily get your hand in front of the fans without your fingers getting hit by the blades. That being said the fan seem like they're really getting after it from what I can see and if I put a piece of paper on the front of the radiator it gets sucked to it flat right away.

marc abrams

Okay, the air flow is good. If you let the car idle for 15mins will the fans turn off eventually after they come on?

Last Lemming

No. Once they kick on the stay on

marc abrams

I would take the radiator to a radiator shop and let them check it. Sounds like the fans are not removing the heat from the radiator. I know that you said the radiator is new but you never know. Let us know how you make out.

Last Lemming

While certainly a possibility - why would the car cool just fine once on the move?

Charlie

A couple of thoughts. Was it doing this before replacing the water pump? Was thinking the impeller on the wp shaft could be slipping.

When you put the new radiator in was the thermoswitch corroded badly. If so that can act as an insulation, make sure it is good and clean and functioning properly.

marc abrams

I was rethinking this. The odds of the radiator being blocked are rather low.
Is it possible the small radiator vent hose (left radiator tank to expansion tank) blocked keeping the radiator air bound?

Last Lemming

I can't really tell if it did it before since I pretty much changed it out when I first got it.

As for the impeller - it depends on how it's attached. I did mark pulley relative to what seems like then end of the shaft and I haven't seen any rotation. However if the impeller is pressed on to a shaft behind the pulley then slippage is possible I suppose. It's a new Laso pump. I wonder what the fail rate is on them.

Last Lemming

Thermoswitch and ragdiator are new. And the fans do come on when they are supposed to

951Tom

My fault Last Lemming, after looking at your video, I realized the foam strip mounts to the shroud that goes under the intercooler & butts up against the top of the radiator.

Another thing I'm wondering is the fans aren't receiving enough voltage so they are turning slower thus not moving as much air. They should cycle on and off at idle.

Jfrahm

I had a spun water pump impeller and it'd overheat at speed. It seemed to move a little water at idle but no way enough when driving, even slowly.

It sounds like the radiator is dropping heat appropriately at idle with the fan running. If true this means you do not have enough water flow through the radiator at idle, or too much heat is being produced.

You say the thermostat is new but is that new, replaced since the problem was identified or new from some other work? I dislike running without a thermostat (fat running, carbon deposits, etc.) but it'd be worth trying.

I wonder if it's just leaning out or otherwise running hot at idle? Or maybe always? O2 sensor?
The cat inlet and maybe the hotside should glow red at 525F or so and if this is happening at idle that's probably no bueno. It might take a while to heat up the hotside but the cat, before the heatshield and just after, should get hot quick.

thomasmryan

I am in the sheared composite impeller group set on the original 22 year old water pump.

Last Lemming

I have a new Lindsey Racing exhaust with cat. The new thermostat I replaced a few days ago does seem to keep the car cooler. Usually when I come to a stop, under the old thermostat, the needle kept moving from the normal position between the two white lines all the way to the top white mark until the high fan kicks on. Once they kicked on the temperature did not drop but held the needle just under the top white mark. Now with the new thermostat when the lowfan kicks on it holds the temperature about an eighth of an inch below the second white mark and it does not seem to creep up at all - but the temperature does not drop either - however the hi fan doesnt kicks on either. So that is an improvement.

One caveat here is that the AC condenser radiator is not on the car currently. It is getting tested and cleaned so I don't know how much that had to do with hindering the cooling process however it was not dirty at all on the outside when I took it off.

I also bled the system very well and even rented a pump to pressurize the system to get rid of any extraneous small bubble.

One thought I'm having is the impeller does not have a tight enough tollerence and I could just not be flowing enough coolant at low RPM because the gap between the back of the impeller in the block is too great, but at higher RPM it follows enough

Jfrahm

Some observations before I forget, stock 1992 968.

72F degree day, sunny. Exterior temp gauge showing 75-80F due to sun and hot roads.

Fully warmed up after 25 mile drive. Radiator hoses near radiator, idling in the driveway, 195 degrees in 145-150 degrees outlet.
On the highway, top down, AC on, 75 mph I get almost to the top thin white line on the gauge.
AC off, 75 mph, at middle of the gauge
AC off, 60-65mph, maybe 1-2mm over the lower white line
AC off, 45mph, pretty much on the lower white line
AC off, 25mph (neighborhood) just below the middle of the gauge (note, warmer than 45mph cuise)
AC off, idling, just above the lower white line. Some fans running.

mikey_audiogeek

Ignition too retarded at idle? Creates more heat.

Cheers,Mike