Hi all!

I called the Chevy dealer in town yesterday to see about getting a Radiator Cap for my 1997 Saturn SL2. I picked it up and brought it home and noticed that the cap the dealer gave me is an 18 PSI cap, but the one that’s on there is a 15 PSI cap. Is this ok? It fits and all, but I don’t want to damage anything.

To give you a little background, my coolant light started flashing a couple weeks ago, so I thought I would remove the tank to see if the sensor inside the overflow tank was sticking because it looked pretty cruddy. I noticed a small crack, so I went to Autozone and bought a new tank. I replaced it and thought everything was fine until it started flashing again the next day. I looked and saw that, the radiator was now dripping steadily. I brought the car in to have a new radiator installed and thought everything was good. But then, four days later, the light came on again. I filled it back up and noticed there was coolant on the top of the new tank. The next day I went to check the coolant level after I turned the car off and noticed when I popped the hood that coolant started pushing itself out around the cap. I bought a new cap at NAPA and the next day the same thing happened after turning the car off. I then noticed a cheap Napa cap wouldn’t stay on tight. It got to a certain point and then just kept spinning like it was stripped. I brought the car to a different mechanic who changed the thermostat and told me that it could be the Autozone tank and if it happened again to go to the dealer for an OEM one. Of course as soon as I got home it happened again right after I turned off the car and popped the hood to check it. It only seems to be happening after I turn the car off. I figured I’d try to replace the cap with one I bought at the dealer before replacing the tank I just bought but it has a different PSI. I don’t want to hurt anything so I thought I’d reach out to you smart folk.

Any thoughts? Thanks in advance!

 

Just popped my hood on my 97 SC2 (same DOHC engine) and it is indeed a 15 psi cap. I have replaced the tank as well due to dry rotting of the plastic and the propensity for them to develop cracks, holes from rubbing against other surfaces, etc.

Most of us get our parts at rockauto.com.

Dorman makes a coolant recovery tank that fit just fine on my 95 SC2.

DORMAN 603121 {#21030881} Coolant Reservoir (Includes Level Sensor) $33.79

Interestingly, the coolant recovery tank cap offered by all manufacturers is 15psi BUT the GM OE one from AC Delco is listed as 18 psi. That is likely how you ended up with the 18 psi from the dealer.

More interestingly, there is a comment next to one of them that states 15 psi but also states (SAE range 14-18 psi). Never really thought about the accuracy of the relief pressure mechanism....so it seems to imply that a cap marked 15 psi will vent the system somewhere betw 14-18psi.

That of course brings up the question of the range for an 18psi cap to vent the pressure.

I have driven DOHC S cars since 1992 and NEVER remember seeing an 18 psi cap -- they were always 15 psi. Personally I would use a 15 psi cap if for no other reason than to be conservative, because you really want to avoid overheating these engines as head warpage can occur, etc.

It sounds like you may be having circulation issues in the cooling system = water pump. Or possibly a restriction /blockage.

When you are driving, where is the temp needle on the gauge?
When you turn the car off but leave the ign in the RUN position, what does the temp gauge needle do, and how fast?
What happens to the temp gauge when you are sitting at a traffic light?

The answers to those questions may help explain things.

When you are driving, the air rushing through the radiator and around the engine provides SOME cooling. But you are likely running at a very high engine/coolant temp.

When you stop moving, if the coolant is not circulating through the system and dissipating the heat at the radiator, everything just heats up further, increasing the pressure in the cooling system until it reaches the venting pressure range for the cap and lets coolant out to drop the system pressure.

Put your hand on the upper and lower hoses attached to the radiator. They should both be warm or hot. If one is cold, then you pretty much know that the coolant is not circulating. Then the question is why not?

 

Thanks for the reply!

I will take a look at the things you've mentioned after work today and report back!

 

Prior to having the radiator replaced the car's temp gage was running a little more than a quarter of the way up at most times. Since the tank and radiator were replaced it's been hovering slightly below halfway once it warms up. It doesn't tend to spike when at traffic lights but it will rise until the fan kicks on.

Both the top and bottom hoses are hot, so it doesn't appear to be a blockage. Neither is cool to the touch.

When I turn the car off then put the key in the run position it jumps up to the temp it was at by the time the car dings twice.

 

These cars were designed with barely enough cooling capacity as it is.
Find out what brand and model radiator was installed.

If your temp needle sat steady at red lights near the 1/4 tick before the new radiator and is now near the 1/2 tick and moves up steadily until the fan kicks in (which was to be my next question), then

1) the new radiator MAY be serving as a flow (rate) restriction (incorrect size, too small, can't dissipate heat of all the coolant fast enough)

2) something got lodged in the passages of the new radiator and is blocking the full flow of coolant through the passages.

Did the shop perform a flush along w the installation? If they did, and did it with the new rad in place (which would make no sense) they would have flushed all the sediment in the cooling channels of the head and block into the passages of the new rad.

3) There is a pressure leak in the system, causing it to overheat at a lower coolant mix temp. After talking to the shop about the brand make and model of the rad put in, and whether they flushed the system, take it SOMEWHERE ELSE to get the cooling system pressure tested for a leak if you can afford the extra diag fee--otherwise ask them to pressure test it since their repairs (t stat and rad) did not solve the problem you brought the car in for (overheating). You found the rad leak, they took it from there and in my opinion have not returned the vehicle to normal operating conditions. So the pressure test should be on them. Confirm this with them so there is no misunderstanding.

Have you tried burping the system? With an ice cold engine, remove the reservoir cap and watch as the engine heats up if you
a) see evidence of flow in the reservoir
b) any air pockets bubbling through the coolant

Having air trapped in the system is much less efficient at heat transfer than the same volume of coolant.

PUT THE CAP BACK ON

 

I was always impressed on how quickly my SC2 got to operating temperature. That said, I'm kind of glad I was running with an entirely new cooling system in the car (new radiator, heater core, hoses, coolant). The thing never overheated even at the peak of summer. As a result, the cap was never stressed.