Okay...so yesterday my 1990 Jeep crept up over the 210 threshold and was midway between center and overheating. I went and got a new fan clutch and thought I solved my problems as it wasn't leaking this morning on my commute to work (temperature was around 65 degrees outside). When I came back from work, the temperature was never over 210 degrees the entire commute (it's 85 degrees outside and I was in stop and go traffic).

I parked the car at home and looked underneath to see coolant raining from my engine bay. I opened the hood and saw coolant streaming from my Mac's expansion tank port by the cap.

What I've done prior to this problem:

New head gasket.
Had cylinder head machined.
New water pump.
New radiator.
New expansion tank.
New thermostat (fail safe 195).
New thermostat housing.
Backflushed heater core to ensure no obstructions.
Ensured springs in radiator hoses.
Filled cooling system by pulling off hose from water pump going to heater core and waited until it came out the water pump port.

How much pressure is in the system? Mac's expansion cap doesn't seem too snug, I would think there would be a little more tension while tightening....is this normal?

This is only happening on hot days in traffic for two days in a row but temp was under 210 (Sensor was working yesterday as it went up to about 230 degrees). Why does this happen on only hot days?

Any ideas?

 

Don't see a new radiator cap on your list.....

 

The Mac's expansion tank comes with a new cap.

I'm thinking about putting on the old one to see if it's a poor fit between expansion tank and the cap they provide.

 

Don't mean it's good....can be tested.

 

btw cruiser54....I went to your link on the renix info....good stuff

I already added new grounds.

 

You need to get on that when you get this cooling system issue solved. What pressure rating is that cap?

 

16 psi radiator cap but I think it's leaking between the cap and tank, very loose connection between the two.

 

Imagine that........

 

I put the big ugly green Volva cap on mine that Cruiser recommends and it helped my temp and it doesn't leak.

Cruiser how in the world did you ever think of using a Volvo on a Jeep?

 

Yeah...silly me for assuming that a brand new expansion tank with a brand new cap would fit together correctly.

 

I didn't. A guy on NAXJA name of Joe Peters came up with that. He worked at a Jeep/Volvo dealership at one point. He must have realized that the cooling system pressure tester adapter was the same between the 2 or something. Anyway, I'm mighty glad he stumbled upon it.

 

What's wrong with you anyway? LOL.

That was a silly assumption.....

 

The Volvo cap is a life saver, I fought that damn cap for years, always leaking. I would buy a new one, and it would leak, I would buy one from the junk yard, it would leak, the only one that hasn't leaked is the Volvo cap.

 

Cheap fix. Even works on the crappy coolant bottles.

Not made by WunHungLo and his comrades......

 

Mine is doing the same thing what it's the Volvo cap I need to try