Just wondering what would cause a radiator with plastic end caps to crack. This has happened twice now, first time I replaced the radiator cap. I never replaced the thermostat but I have a set of electric fans that constantly run and the temperature never goes above 130* (verified with another gauge). Both times it cracked the car was in neutral and revving to about 4500 rpms for a few seconds (while checking timing). Under normal driving it doesn't crack. Both times it cracked I quickly felt the upper radiator hose and it was under a lot of pressure. Neither time had the motor been anywhere over 130-140 degrees.

Cylinder compression is good. Oil is not milky. No loss of coolant. No white smoke or sweet smell from the exhaust. I can't say I've noticed a single symptom of a bad head/intake gasket, cracked head/block etc.

Can a bad thermostat cause this to happen even if the motor never gets to a high enough temperature? Would I be better off taking out the thermostat completely since I only drive it locally anyway?

 

Normally heat, psi and time will crack them.
Are these new rads or used?

 

Both were used. One cracked, had another and it had a hairline split in it. I jb welded it and had the same issue. I don't understand why the upper hose is under so much pressure (abnormal amount) without the motor getting hot.

 

The upper hose gets hard like that. Fairly normal.

 

Would a descent set of fans constantly running make the car never get to operating temperature? Even running 10-15 minutes with the fans disconnected it only gets to 130-140 degrees (verified with two gauges)

 

What temp T-stat do you have in the car?
It needs to get warm enuff to open that.

 

If you only drive it locally taking out the stat is the LAST thing you want to do. You want that engine to have every opportunity to come up to temp as quickly as possible when you're doing a lot of short trips.

Can't say why you car isn't warming up faster, but a new stat would be a good place to start. Might be your old one is stuck open, even if only partially. I would do a fresh radiator cap while you're at it. If yours isn't relieving pressure when it should (~16 PSI) you WILL crack radiator end caps. Normally it's just age, temp cycles and pressure that eventually fatique and crack the plastic, but they can be murdered by excessive system pressure as well. And make sure the line to the overflow container isn't plugged up (acts the same as a cap that isn't opening when it should). You can just blow through the line to see if it's clear.

It's also possible there is an air pocket trapped in the engine and it's preventing proper coolant flow. Some parts will take seemingly forever to heat up, but on the business end (inside the engine) other parts will be overheating. But I'd do the simple stuff first and see where that gets you- stat and cap.

 

Used radiators are like used condoms , they leak ........

 

Not sure why you would buy a used radiator when you can get a decent new one for under $100.

 

Had them laying around but this is a $180 pickup truck radiator. Anyway I redid the entire cooling system and it cycles and runs perfectly. Truck pulls damn good too now that I can actually test drive it lol

 

Still under $100 from rock auto.

 

I bought a used aluminum radiator for my 83Z out of an 83 Firebird because I am religiously trying to restore it. Imagine how stupid I felt when I saw the you can still buy the exact same radiator for under 100 bucks from the local parts store...they haven't changed...