Hi folks,

Been working in my garage addressing a delayed overheat while idling issue on my 97 SC2.

Car idles for 15 min, temp gauge stays below half.

Minute 18, while I'm of course doing something else, the stench of old cooling system wafts across the garage, with a nice small flow of dexcool coming out from between the cap and the reservoir. This cap reservoir pair has been fine for years. Now the cap backs off as everything heats up and when cold, seems to go past the threads and loosen again so that I can never get it quite tight enough.

I replace the reservoir with the original 23 year old one I had replaced proactively. The top fits like a glove. I even put a slow quarter turn extra with a pair of channel locks to ensure it is sealed.

18 minutes later, while of course still doing something else, I look up to see the waft of boiling coolant mix.

Can the reservoir and the cap both behave as defective all of a sudden? Well, that's not fair, I have been very very very very very slowly losing coolant for a year with no residue at the cap.

Which of the two expansion tank caps below doesn't seal properly?

The answer might surprise you.

I left one wet just to confuse the issue if you think you're being smarter than the average bear

A

B

Yes I burped the system

Yes the top and bottom radiator hoses and the hose to the expansion tank are extremely hot

 

Thermo stuck shut? Fans coming on?
how old is the ECTS?

 

Thermo stuck shut wouldn't last that long and hoses would not both be hot.
ECTS allows fan to kick on if the car runs long enough to get hot enough.

The answer is A seals for 30 min, fan cycling, all seems fine, fan kicks on at correct place on temp gauge, but after 30 min idling in place, out comes boiling coolant past the cap with the temp gauge reading at one half.

Having had it over heat three times today, I noticed that the boiling stops and the steam stops within 2 minutes of turning it off. And I can remove the cap with no hiss of pressure.

So I am thinking, based on all of this, I need to investigate the water pump for a leak. I thought this was just a tiny leak at the cap seal but apparently the entire system cannot pressurize fully and it literally just boils at 1 atm pressure.

The fact that it spews coolant with the temp gauge reading one half also seems to point to insufficient coolant circulation. Leak at the water pump would account for that as well. A thermostat stuck closed what also affect that, but if I can run for 30 minutes with full cycling of the fan multiple times, I'm thinking that is not the issue.

Ironically, I couldn't not find my newer bluetooth reader until after the third overheat so I don't know what the coolant temperature was but my eyes tell me it was boiling when it shouldn't be.

Also, I was told many decades ago to always replace the cap after an overheat incident. I assumed this was because the pressure relief valve built into the cap is a one-time deal and or the gasket on the cap may get distorted from the excessive heat. in my case, there doesn't seem to be enough pressure being built up so that doesn't seem to be an issue. So does the overheating damage the cap seal? And for that matter possibly swell the reservoir so that the threads can actually get messed up?

This quiz post was supposed to have a nice simple answer, now it's a diag post.

 

Something about the black locking tabs on the second one don't look right to me, derf. I suspect that they're NOT actually locking things down anymore.

 

I like to pressure test cooling systems as a complete system. Most modern cooling systems have a 3/8” hose somewhere to bleed air to the expansion tank. I add a T to the system and pressurize the entire system if possible. I usually find a bad cap this way without having to purchase special adaptors. It seems that the manufacturers like to change cap and tank threads every few years. Also the coolant tanks seem to fail more often as the vehicle ages, probably just more cooling system ailments over time and the plastic tank is the fuse.

 

Okay this site ate my last post.

Upon closer inspection, you were correct Rube. The black tabs on that cap are not really holding the threaded lighter piece in place. I'm not entirely sure how much this has to do with affecting sealing, but it shuffles around in there and that is not right.

More damningly, I took a real good look at the threads inside the same cap.



Using this cap overheats in 10 minutes

I hate it when the threads are effed up. That cap is old as the hills and I've always tightened it the same way. the system never leaked so I pretty much never took it off. What can you say it is what it is.

Indeed there is a line coming off of the expansion tank that feeds back to towards and below the intake. Might just be routed to the ground . I will have to check . in that case I can't tee off it

For the record, the garage floor was absolutely dry before each overheat so if it is leaking by the water pump it is probably evaporating off of something else hot, something I saw Andy mentioned in a different post from earlier years.

I guess I will get me a dual purpose mighty vac pressure hand pump as my vacuum mightyvac is used only for brake bleeds as I don't want to ruin an expensive multifunction one should I ever get brake fluid in it.

This car has spewed more coolant in 48 hours than it has in the past 23 years.

And every overheat has been in one of my driveways or garages. Suppose it could be a lot lot worse

 

Maybe a zip tie around the perimeter of the black tabs would hold it in place? IDK, just speculating.

 

I didn't think it through. Haha

 

Ok, did some more thinking.

For the car to idle for 30 min and the fan to cycle on and off repeatedly, everything in the system must have been operating properly. ECTS turning on fan properly, water pump circulating coolant, thermostat open when it needed to be, cap seal holding.

So what will lead to the ECTS reading in the head to be normal with coolant out the expansion tank?

Bad etcs or lack of coolant circulation.

ECTS is fine based on normal fan cycling.

So lack of coolant circ. Water pump or thermostat misbehaving. It is a 195 thermostat and to be honest, I never checked the temp via ECTS when the fan is on. I don't know but I'm guessing that it might be cooling the coolant below 195.

That would check if the thermostat to begin to close. It may close, it may close partway

However if it sticks part of the way or all of the way closed, it will cut off coolant flow throughout the block when The coolant in the block is at its lowest, right after the fan turns off. And when the thermostat doesn't open as the corn and the block heats up, it's basically creating a pressure bomb where the only pressure relief is the expansion tank . The cooling gets hotter and hotter but is not moving oh my God expands and increases in pressure until the cap gives period once it does, the pressure relief is over with so there is no residual pressure when I take off the cap.

What was the last thing I did to the cooling system on this car? Replace the thermostat.

Proactively.

Do not buy the AC Delco thermostat for the s cars. I found it was exactly the same as some cheap *** brand on RockAuto, and reviews on some of the Saturn forums basically said it was something that wouldn't last very long. But I put it in. And here we are. Going to buy a stant.

 

Don't look now, but whenever I do proactive part replacements, I always keep whatever it is that was in there...





I need to get a new cap I do believe, because the pressure relief valve has been triggered. That is how the fluid is getting out. Then I can pressure test, make sure there is no leak, then drain again and replace thermostat or shall we say reinstate thermostat. Should probably track down the gasket