M03

Hello, in January I replaced timing belt, water pump, thermostat, and radiator. The radiator was not planned to be replaced but the upper inlet was disintegrating. Since then, I've had coolant problems. Under load, like going up a hill, the temp starts to creep up, but when coming back down the hill, it cools off. About every week and a half to 2 weeks, I have to do a full bleed and add coolant. There is no signs of leaks and I expect my coolant loss is from when it overheats. My heater works when it runs hot, but when it's at normal temp, it some what working. I dont know where I should be looking for my problem since there is no puddle where I park and I bleed the system correctly so no air bubbles should be in the system. Any help would be appreciated, thanks!!

sdls

If you’ve bled the system and there really arent any external leaks like you said, yet still have to keep adding coolant and lost cabin heat...

Ya gotta do a sniff test on the coolant to look for the presence of exhaust gases
Good luck

Einzelherz

Just to make certain, you're bleeding the air using the screw on the top of the engine right? Is it possible the thermostat was put in upside down?

M03

I am bleeding it correctly and also use a spill free funnel. The thermostat could be upside down, I really wasnt aware of the jiggle thing until after, but would that really cause the car to over heat?
Sniff test? What is this?

RA40

iTrader: (6)

Check that the heater control valve is not leaking. That's an age issue with many LS's. Do not use worm drive clamps, use the constant tension clamps like Toyota uses.

M03

I'll double check the heater valve when I do another fill and bleed. I dont think its leaking but I'll put my hand around it

sdls

it’s the last resort. I think it’s called a block tester. It adapts to where the radiator cap would go and changes color if exhaust gases are detected.

M03

I'll check my local auto parts store for one. I have a bad feeling it is head gasket and really sucks if it is since I just invested all the time and effort for the timing belt. The car hasnt ran any different since then, just this overheating issue.

bradland

Head gasket issues on UZ motors are EXTREMELY rare, almost non-existent.

M03

That's what I've heard but I cant find any leaks anywhere.

bradland

Also, how do you determine it’s Full or Low?
I remember my 99 would look a little low by the reservoir marks so I would add coolant. I thought there might be an issue but eventually realized it would never drop “too low”.
I finally left it alone and the level stayed slightly below the Cold line and never moved.

M03

When I Fill and bleed about every 2 weeks, it chugs about a gallon once the thermostat opens. I've been using a no spill funnel so, i go by if the water level on it when filling it.

timmy0tool

iTrader: (7)

i'm willing to bet you still have air in your coolant. it took me over 30 mins of bleeding to get most of the air out (and i still think there were bubbles in there). by you stating your heater works intermittently tells me you still have air in your system.

what is your method of bleeding?

Superfast1

It's possible that the jiggle pin or check valve on your new thermostat wasn't placed in the correct (upright) position so your system has had a hard time purging all the air out that's why the temperature is fluctuating instead of being constant so open it back up & re-check it.

bradland

Def check the heater valve as RA40 mentioned.
2 more possibilities-

There’s a short bypass hose approx 4” long x .1875” diameter under the thermostat above the water pump. If it’s compromised the water is likely steaming off and it’s tough to see unless you’re looking for it.

Check the line between the reservoir and radiator. It’s designed to move coolant back and forth as heat causes the volume of fluid to fluctuate. If it’s only allowing fluid to move in one direction, for whatever reason, you’re losing fluid via the small hose venting the reservoir every time the engine heat cycles. Detach these small hoses and shoot compressed air through to verify healthy flow is possible.