Surge Tank Leak at Radiator Cap -- Help!
 

Superformance Surge Tank Persistent Leak

I pressure tested my whole system to 19 psi and it held rock steady for an hour and a half. I also removed, tested and replaced the thermostat with a Stant Superstat 180 degree part number 45358. I just returned from a 10 mile drive to get everything up to temperature and this is what I get. Everything I try ends with the same result.

I monitored my temperature and it never got above 195 on the coolant and 205 on the oil temp. (very cool out today) I am running 50% OEM green coolant and 50% water. Boiling point should be way above that.

All I can think of is that the leak occurs at temperature but I can not confirm if it's where the radiator cap tank neck is welded to the surge tank or the primary radiator cap seal on the inside or if it's the seal between the surge tank and the radiator cap. The original cap that came with the tank had a similar issue. The cap that is on the surge tank now is a Stant 10230. 16 psi. When tested the cap actually bypasses to overflow at approx. 14 psi.

The other odd thing is that I am getting coolant moving to and from my overflow tank which should not happen with my temperatures and a 16 PSI radiator cap. I am filling the surge tank to about 2/3 so there should be more than enough space to allow for expansion.

Help Appreciated

Attachment 26700

I would start with a brand new cap.
If it still does it go to the next option.

I had a similar issue after I changed the cap. I put a 16 lbs Rad cap Sacrificial Anode Radiator Cap Stops Electroylsis RC 35 ve Labs Radcap | eBay and it keep leaking. I changed it to a new one and it was fine. I fill my tank maybe 1/2 full.

Scott

Part Number
 

Does anyone know the correct radiator cap replacement part number?

I currently have a Stant 10230 16 PSI

There is no cross reference that I can find to match the original cap.

Check that small hose connection clamp.... the clamp does not look to be compressing the hose tightly in the photo. Car will discharge some coolant after a refill to attain the proper coolant level in the expansion tank thru that hose. The coolant discharge could be just that. Contact me off line if you have other questions I can help with. There is a divider plate inside the expansion tank with a hole in it. you can feel it with your finger if you stick it in there. That is the proper level for the coolant. Also empty you overflow tank, it is probably filled with overflow coolant too.

Check the rubber seal on the existing cap for cracks or missing edge pieces or just replace it. A little dielectric grease on the rubber seal of the cap doesn't hurt either - promotes a better seal and less effort to remove the cap later. I fill my expansion tank about 1/2 full.

One other thing that I never saw mentioned and this happened to me once on one of my cars is the small outlet tube for the overflow came loose and my pressure tester would not show anything. But I could drive it for a little and there would be coolant leaking. Finally I cleaned and dried everything off around the radiator cap neck and then started looking by trying to move something and that small tube had a very small crack in it where it was soldered to the neck. I had already changed radiator caps, checked the hose from the tube to the overflow tank, and that was all that was left. I soldered it again and never had another problem.

Ron

I had a similar experience with my surge tank that I bought used. The prior owner said he had pressure tested it and it was tight but upon installing it I had a slght weep around the soldered flange when hot. I took it down to the radiator shop to see what they could do with it and when I went back they said they had a real hard time finding the seep because it would hold pressure just fine when they aired it back up. After several repeated tests they finally did spot a very small seep and soldered it up. So apparently pressure testing these tanks isn't always a sure thing.

Replace the radiator cap with a stant cap at your local auto parts store. They all fit.

Surge Tank
 

I just purchase another radiator cap. Stant 10230 16 PSI This will be my third but at $6 a piece I would not rule out faulty craftsmanship.

I am also going to do a combustion leak test with a block tester I picked up at NAPA. I just want to rule everything out. I have a feeling my coolant pressure is higher than it ought to be given my engine temp. The block tester is a pretty simple tool and cheap piece of mine at $40.

NAPA AUTO PARTS