My daughters 94 Z28 is overheating after replacing the water pump, thermostat, sending unit, and new coolant. I tried bleading the two bleeds above the thermostat housing. Replaced fan relays. Still overheating. But, heater not blowing hot air. Fans kick in, but run slow.

Ideas Sugestions?

Pluged heater core maybe?

I disconected and blew thru the hoses and got plenty of fluid flow before and after the core. I am going todo a flush today of the whole block.

JohnsonB

I had no overheating problems but had no heat. I used one of the prestone flushes and replaced the dexcool (red antifreeze) with prestone dexcool approved (more red stuff). Still no heat!! Pulled the heater hosed off the firewall (not fun) and flushed the heater core with fresh water for about 15 minutes. I thought I had ok flow but opted to reverse the flow and within about 3 minutes of doing so it plugged and sputtered and spit a clump of mush and then the thing really flowed. Hooked the hosed back up and now have heat like you can't believe!!

I did some research and it seems the green coolant doesn't mix well with the red (causes a thick white goo! ) and the green is susposed to be too harsh for the alum parts. If the inside of the block and core get coated with this thick crud it will hinder the heat transfer...

Also try running the car with the air on as it turns the fans on, Mine sits steady at a lower temp when sitting with the air on. Without it it climbs what seems like a lot but never really over heats. What temps are you seeing?

It gets to 240 F with in 10 minutes the first time. I am on the way to get a flush kit now. Thanx for the tip on the red anti freeze. That could be it. She ws told by the dealer last March she had fluid that had been mixed, now it makes sense. I will let you know how it goes. I was also told by a friend to try testing the radiator cap for the right presure. If it is week, it can suck air.

JohnsonB in Washington

DjD has it right. NEVER MIX THE TWO! Green on top of Red is worse than the other way around. Some of the silicates and other additives of ethylene glycol (EG) precipitate out of solution to form a goooey mess. Pressure flushing is the only way to remove this and if it's in your heater....it's everywhere!

Today's newer EG forulas are as good as proplyene glycol(red/Dex or PG) on aluminum parts. The issue used to be that the EG was not as good at keeping conductivity down due to the acidity of the product. This has changed just in the last few years and I run EG in everything I have with no problems.

The radiator cap has no functional purpose other than closing the system. If it is weak, it will allow coolant past the cap during high RPMs or when building pressure due to rise in temperature. If it is not pouring out coolant by now, it's okay but changing it for maintenance's sake is a good thing! But,the cap is not the problem.