Check/replace your radiator caps

[Legacy777]

I had an issue the other week where the car started getting warm, and the radiator fans wouldn't kick on. I thought it was the sensor, but the problem resolved itself...

More details here
http://bbs.legacycentral.org/viewtopic.php?t=34800

Anyway, I bought a coolant pressure tester. Turns out my old radiator cap wasn't cutting it, and coolant was leaking past the cap. The system would hold about 10 psi before it peed coolant out. Which would explain some previous mysterious coolant I've noticed on the garage. Replaced the cap, pressured up the system, and it held. I let it sit for about 30 minutes.

So I think that will take care of my cooling system issues. I tested the cap for my AWIC system, and it hold about 6 psi. I'm not sure that's my sole problem, but I'll start there.

Also, for future info.

The radiator cap opens @ 12.8 +/- 1.4 psi & -0.7 to -1.4 psi

When testing the cap, it should hold the service limit pressure for 5-6 seconds.

Radiator cap service limit is 10 psi
Standard pressure range is 11-14 psi

When testing the cooling system, pressure system to 23 psi.


Also, just as an FYI, the older radiator caps seem to be slightly higher pressure, 0.9 bar, and I think my old cap was the same pressure. The new caps have 88 kPa stamped on them, which is slightly lower, and seems to match the info in the FSM.

0.9 bar = 13.05 psi
88 kPa = 12.8 psi

[dropdfocus]

Good stuff to know.

[BXSS]

+1 good info!

I had problems with a Greddy 1.3bar radiator cap on my OBS-t.
It work fine for about 2 years no probs @ all.
After that it would allow coolant into the overflow bottle but would not let the coolant back into the radiator.
I thought it was a HG prob, so I did a hydrocarbon test on the coolant - which came out clean.
I had a stock .9bar cap laying around slapped it on & problem was resolved.

I then put a OEM Honda motorcycle 1.1 bar cap on the car & have been OK for the past 3 years.

[DLC]

I wonder if this has anything to do with my overly warm car after long drives and heavy loads. Seems to lose coolant mysteriously.

[Legacy777]

Could be.

It just so happened because I kept my n/a radiator, the cap was on the radiator when I was testing through the coolant expansion tank. Typically the testers can't test the seal portion that seals the cap to the radiator, only the part that seals the coolant from the expansion tank. For a $10 part.....if you're in quesiton, you may just want to replace it.

[chochocho]

i have an aftermarket radiator with radiator cap and another cap for the coolant expansion tank. both of them have the 1.3 bar radiator cap. i wonder if that could be the cause of my lost coolant on the ground. what do you all think?

[dropdfocus]

It's very possible that could cause your problem.

[bmxpunk]

I know subaru has a tech bulletin on replacing radiator caps and I would say even on the newer cars, about 75% of the ones I test fail. One week in November, I ordered about 8 in like 3-4 days.

I have beeen wondering as far as caps go, are the Sti/greddy/cusco/whatever caps that are rated for more pressure harder on headgaskets? I know the new 4-stroke dirt bikes have options up to 1.9Bar, but those heads are o-ringed, if I remember correctly.

[Adam West]

Great Q. Watching this for answers.

[DLC]

It would be interesting to find that a weak and/or malfunctioning cap is actually making head gaskets more prone to go, simple because of the pressure difference between the combustion and the cooling side. If there was more balance, perhaps they'd be less likely to fail?

I'm going to replace mine very soon, as it's probably original, and I'm having cooling quirks.

[bmxpunk]

DLC,
you said your car gets warm after long drives or high load. When did you last change your coolant? I have seen foresters that act normal under normal driving conditions, but once you turn on the AC and go up a hill mash the throttle like to pass someone the car gets very hot very quick.

Not quite sure what causes it but the foresters I have seen in particular didn't have a lot of miles on them and I believe they were within the maintainance schedule, but they developed like a cement in the core and I would not flush out. (possibly the "cooling system conditioner?")
By the way and for what it's worth, subaru looks down on flushing, we are told only to drain and refill. And i am looking forward to the new blue "super coolant" that comes in the New STI.

[DLC]

The coolant has been changed in the last year.

My car last summer would get a little warm with AC on going uphill, but in the winter it only heats up when I've slowed down or stopped after driving at highway speeds.

I'm on my third radiator, as the previous two got clogged with the cementish/gravel stuff, and I'm avoiding the Coolant Conditioner at all costs.

I am losing coolant somewhere and somehow, but I'm just not sure where.