NJRoadFan

My 4kq when I had it running always ran a tad on the hot side. It runs above the halfway mark say 3 ticks (or was it 2? I can't remember) below the top of the gauge and then the radiator fan kicks on. This is with stop and go driving around town as I feel this car isn't ready for NJ's hell on wheels highway driving. When I test drove the car I seem to recall it happening fairly quickly (about 5 mins), the other times I drove the car it took longer, say 15-20mins, next time I run the car I'll time it. I know I have a small coolant leak somewhere as the damn coolant light blinks like crazy although the level doesn't seem to drop all that much in the tank. I can verify that the t-stat is opening simply because the radiator is getting hot enough to trip the fan. Water pump seems to be doing its job, otherwise I wouldn't be getting any cabin heat. The dash gauge sender seems to be somewhat right as I get nice BURNING hot air from the vents. When I open the expansion tank cap after a good run I hear hissing and gurgling of coolant from releasing whatever system pressure there is, but I don't get a volcano of coolant, its kinda like a bottle of soda. At no time have I had steam gush out or any sort of explosion under the hood while driving. Are these indicators typical of a cooling system not pressurizing enough or really gunked up?

I checked over my cooling system and the following seem amiss.

-Cracked expansion tank at the top, right near the fender. I'm going to try to epoxy this one shut. Don't see any other cracks.

-I see stains of coolant where the upper rad. hose meets the block. I'm going to assume this is leaking under pressure, would tighting the clamp help in the meantime?

-Green Prestone.... nough said.

Finally I'm crossing my fingers that this isn't the sign of a slight head gasket leak. I DO NOT have any of the classic signs listed below (thankfully)

-white smoke or coolant smell (that my nose can find) from exhaust.

-oil in coolant or vis versa. (no JT insta-milk shakes)

-exhaust smell in coolant (smells like dead fish, just like every other Prestone/Dex-Cool filled car, the bittering agent I believe)

I have NOT yet run the engine to see if bubbles are coming up into the expansion tank. Will do tomm.

I was planning on rebuilding the cooling system come spring time since I know the hoses and other bits are original, I was going to keep the original radiator and replace everything else. My intern fix is to do a complete system flush and put in the proper blue G11 coolant, hopefully it solves the problem until I have time to do the rebuild. I hope it isn't a headgasket leak, otherwise I won't be a happy camper. If I can't resolve these cooling issues its likely I'll have to mothball the car until the springtime when its light out past 4:30pm and it isn't freezing. (although its abnormally warm for December around here at the moment)

AudiSport4000

Sounds like normal coolant gauge and fan operation to me. My fan does the same thing during the summer months, or when its warm outside.
If you are getting a coolant light and the level is fine (filled up to the MIN mark at least!) and the car isnt overheating, the level sensor may be faulty. The coolant also sloshes around during hard cornering, that may trip the light too.
Make sure all hose connections are tight. Depending on if your radiator is plastic or metal, be careful tightening the clamps on it.
When you have just run the car and turn it off then attempt to remove the cap, do it slowly. It will hiss and coolant will move back into the tank. It shouldnt spill all over, unless you do it very quickly (which is super dangerous).
Depending on your climate, the car may leak coolant at night. I had this problem recently, the thermostat housing bolts werent super tight, causing a leak at night.

Nefarious

I'm having the same issue with running a little to hot for my liking. Already did a full flush including some of that rad flush solvent stuff. Replaced the T.stat & housing (source of my leak) as well as upper/lower rad hoses. I just can't seem to get it to run below 2 ticks from the top.

If you figure it out let me know.

NJRoadFan

Had some spare time before dinner and jump started the car, I figured this would be a good time since the battery needs a charge anyway. My observations below of the cooling system was when the car was just idling with some light revving of the engine every once in awhile with the hood open. Outside temps were approx. 52 degs. F.

Car takes about 15 mins to totally warm up. Gauge eventually climbs to the 3rd mark from the top and then the rad fan kicks on for about 3-5 seconds, after which the gauge drops slightly to between the 3rd and 4th line. After that it just hovers in between with the fan cycling on and off. I confirmed my head gasket was intact (thank goodness), no jacuzzi in the expansion tank. I guess these cars run hotter then "normal" compared to other car's coolant gauges. I did notice when I turned on the A/C that the rad fan did not kick on, I'm not too concerned about this since the A/C needs a recharge anyway and this is a winter car.

During this test case I noticed 1 or 2 lifters click and clack (don't know what kind of oil is in this thing, will change it soon) and the fuel pump buzzes, good thing I got the filters on hand to change out when I have time. The engine bay looks like a disaster, but hey the damn thing runs like a top.

kelbrig1

I've cleaned up the sender for the gauge and had better luck with it reading lower, but as long as your fan is cycling as it should, everything you said looks fine.

4corners

Cooling op sounds fine. Fix that cracked expansion tank though and check all hoses.

AudiSport4000

Sounds like normal operation

TCP

Part of the problem may be the cracked tank. The coolant system usually runs at 10-15psi to increase the boiling point of cooland. If you are not getting and holding proper pressure, chances are you have a few hot spots inside the system where the cooland can reach boiling more quickly than designed. Everything else sounds completely normal. These guages are built to be linear in operation...they show actual temperature. Most modern guage systems are "weighted" to remain steady in the middle of the guage through a wider range of temps. they don't move around in regular driving, "frightening" the operator.

VWrally

My 85 runs way cool, like on a road trip back from mt baker it was barely over the first tick above the bottom! an most of the time it never hits the halfway mark. my buddy has an 86 that he just replaced the entire coolant system less the radiator and his runs similar to the car described by the OP. any thoughts to why is mine so much cooler than most?

Blewtoon

Possibly a lower temp thermostat. Fan switches come with various temp settings too.