My 96 Safari van has a weird issue with cooling.

On very cold days, when doing the morning warmup, the Temp indicator does not move, and heater/def blows not very warm air, almost cool air. But when I drive it a short distance,,, the Temp comes up to 190 + or-, and heater/def blows hot air, like it should.

Put in a new 190 thermostat yesterday, no difference.
New water pump this fall
Radiator is full of antifreeze
Even after driving, the top of radiator is not very hot.

If heater core was partially plugged, I would not think it would blow hot air any time.
It does have the rear heater,,,, I was wondering,,, if because of that, the cooling system was getting cooled down more because of the added plumbing for rear heat. Rear heater blows hot air at road speed too.


All works fine at driving speeds,,,, and the temperature of air air being blown does follow the temp gauge, up and down,, this is not a real problem, just more of a mystery.

So your saying its only blowing hot air while moving? and it takes a while to warm up at first?

yes,,,, all heat and def in entire vehicle works like it should while driving,,,, very toasty warm, and temp gauge is up.

On a cold mornings, if you go out and start it, and just let it idle temp gauge will not move,,,, and not very warm air,,,,, I have never had a vehicle do this,,, any car/trk I ever had you could get the vehicle warm inside after letting it idle in driveway for 10 minutes or so.

Like my truck,,,,after I let it idle a bit, blows hot air ,,,, basically, after running a while it reaches operating temp even at idle, and blows hot air,,,,, air temp and engine temp change very little while driving.

Never had a cooling/heating problem when I had my 96 Astro, I don't think the rear heat has much to do with it.
Have you tried to bleed the system? I know with the extra complexity of having the rear heat, you have that much more space for air to take over and displace coolant.

I'd take the radiator cap off, and start it. Let it sit and watch the level of coolant in there. See how long it takes before the level drops when the thermostat opens. If it takes a long time, I would suspect air in the system or possibly another bad thermostat. You can test the thermostat by heating water on a stove (in a non-food pan) and keeping a thermometer in the pan to watch. It should open up when the thermometer hits the right temperature.

But honestly, it sounds like air trapped in the system. If you get an air bubble near the sending unit for the gauge, it will hold the cold air in a pocket there and not change. Same for the thermostat, it holds a cold pocket of air next to it, and wont open. I had this problem and went through 2 thermostats on my 91 G20 Van before I really bled the air out (had rear heat too). I think having the extra plumbing makes it easier to trap air, but that'* just my opinion. Once you start driving, the increased rpm of the water pump will force air into a different place, and then things work the way they should. But on a cold start, the trapped air is gonna just sit there.

Well,,,, will try your suggestions, SS8704. Something is a little out of whack,,,, but I would think,,, once things got warmed up, and after driving for a while with coolant circulating constantly,,, that air pocket would get dispersed/eliminated. with the overflow tank and such, it is not really like a brake line closed system. How about the fan clutch ??? maybe it is not 'clutching'. Right now I do have the top of the fan shroud still off, as we just did the thermostat change out Tuesday. I know you need the shroud for proper operation,,, but this super cooling system acts the same with shroud on or off, just have not put it back on yet. With the old thermostat,,, nothing was different with top half of shroud on or off. This thing is just buggin' me.

Like I said, top of radiator is hardly warm after long drives, bit if you loosen cap, [or flip cap pressure release tab ] after driving, it will squirt a little coolant into overflow.

Is there guide or 'how to' sheet on how to 'bleed' the cooling system on a 96 Safari ?

all you have to do on that is park it on a small grade with the rear of the car lower and run it with the cap off for a while

You may want to look at two things, assuming the work you have done prior is functional.

1- reclean the heater core. They are known to clog on your vehicle, a easy way to clean it is with a pressure hose (LOW PRESSURE) at the self serve car wash, going straight to the heater hose opening in the firewall. The car wash equipment will get right in there.

2- do a pressure check. You have a 4.3L in your vehicle, and they go through LIM gaskets like crazy. This causes issues indirectly with the heater. That LIM gasket may be the indirect source of your problem (I did note you stated your radiator was full).

Not sure if your van has one or not, but look on the top of the thermostat housing to see is there is a screw there. If there is, that is a bleeder screw. Just back it off slightly with the engine up to temperature, and keep it open until coolant (instead of steam) comes out.