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1G Could my coolant be leaking?

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Car's running more or less fine, somewhat rough idle but I don't think it's coolant related. But, as part of my annual fall checkup to prepare for winter driving, I checked the coolant level to both make sure that there was enough coolant and that the ratio was sufficient to protect against the low temps we get around here (I mix concentrated coolant with distilled water to save money and fine-tune the ratio).

Turned out that the coolant was a bit low and the ratio too thin. So I drained some coolant and then topped off with concentrate after removing the coolant cap just above the thermostat. Drove it around till it reached operating temp, let it cool a bit, then checked the level and ratio. Still too low on both.

So I repeated this until the ratio was just right. But every time I remove the cap, the coolant is well below the cap opening and there's just barely enough to fill the coolant ratio tester (I used the kind with a rubber bulb like a turkey baster and a clock-like gauge).

Is this normal, for the coolant level to be this low, and for the ratio to have been this low as well, or is it indicative of a slow leak and perhaps something else? There's no sign of oil leaking into the coolant or vice-versa, so I don't think there's a head gasket leak.

Nor do I see any obvious signs of leaks anywhere (although I haven't done an exhaustive inspection yet), so if there is a leak then it's very slight and only when driving the car and evaporates before it leaves an obvious mark anywhere.

When I flushed out the coolant last spring I'm pretty sure I had the right ratio. And the reservoir is at the right level and doesn't appear to be going up or down. My recollection is that in the past when I've filled the coolant up to the cap level, it stays there and doesn't go down much.

Oh, last thing. I replaced the original cap with an aftermarket one, the kind that has a release valve. Could that be where coolant is leaking, as steam, and would it leave a telltale stain on the inside of the hood?
 
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XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Do you have a pressure tester to check for leaks real quick?
No but I can loan one from a local auto store. I kind of suspect that it's the new cap, though. None of the most obvious signs of a leak.
 

luv2rallye

DSM Wiseman
8,441
1,202
Jun 7, 2003
Minneapolis, Minnesota
I've never had luck with the release valve cap. Get yourself a Stant cap. Also your problem may be due to not burping all the air out. With the cap off, squeeze the lower rad hose a number of times to burp the system. And fill the overflow tank when engine is hot. Then let it cool overnight during which (if no leaks) it will draw fluid out of the overflow tank to top itself off.
 

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Does the valve cap leak coolant steam when under pressure? Also, I was squeezing the top hose, not the bottom. Maybe that's the problem. I haven't driven the car that much since I replaced the coolant, several hundred miles, so hopefully air in the cooling system hasn't led to cavitation issues yet. Thanks.
 

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Heat is fine, it's like an oven within minutes, and temp never gets beyond the 45% point. So maybe there is a small leak? Or, perhaps, still a lot of air in the system that I haven't fully burped out, so when I add more coolant, it only replaces some of the air but not all of it? Aren't you supposed to be able to bleed the system by running the car with the cap off?

And, what did you mean by not having luck with valve caps?
 

luv2rallye

DSM Wiseman
8,441
1,202
Jun 7, 2003
Minneapolis, Minnesota
Air in the system won't get completely out without proper burping (and coolant level will be affected). Burp first, then if still have problem do a coolant system pressure test (both system and cap) to look for leaks.
 

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Valve caps have a little red lever on them to release pressure. Typically if they fail though the car pushes coolant into the overflow container.

The only way to know is to do a cooling system pressure test.
I was going to completely clean and overhaul the intake, exhaust and turbo, replacing all the vacuum, coolant and oil hoses, o-rings, gaskets, etc., but other obligations and now cold weather have put that off till spring. So I'm going to have to make do until then and only take care of more serious issues.

But, sounds like I first need to bleed the air out of the cooling system properly, as I've been doing it the wrong way so far. Hopefully that'll tide me over till spring. The car's not showing signs of overheating, so I'm just being overcautious.
 

chrysler kid

20+ Year Contributor
2,610
579
Dec 20, 2002
Mckinney, Texas
Yeah investing in the coolant burp kit, the big funnel with the cap adapters is a good purchase. Usually you get more than just air bubbles coming out, you'll see dirt and contamination float up as well

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wparks

10+ Year Contributor
85
46
Mar 19, 2012
Fort Collins, Colorado
I love those red lever "instant pressure relief" caps for my farm trucks, but I have weened myself off of them for my cars as they tend to encourage bad habits (opening system when hot) and are really not necessary if you do basic maintenance to keep the coolant system healthy.

In my experience, by topping off the coolant after you have driven it, by the 2nd or 3rd time you should have all of the air out of the main loop- the cap is the highest point in the system and air will collect there as it cycles. I also assume you are keeping the overflow reservoir at the full line. The standard coolant cap has a spring pressure regulator that maintains coolant pressure by burping over-pressure (excess coolant) out of the main loop into the overflow reservoir when it heats and expands, then a relief valve that allows coolant to be sucked back into the main loop from the reservoir when it cools and contracts again.

If the cap and reservoir are working properly, your system will naturally burp the air out on it's own and keep the main loop full and happy will little or no air under the cap by drawing in only coolant when it cools. Since you are seeing air in the main loop after several drive/cool cycles, I suspect the new cap may have a problem- either leaking too much coolant/pressure out into the reservoir and not maintaining the proper coolant pressure in the main loop, or more likely may be sucking in air or not sucking in coolant as the main loop cools.

Make sure there are no cracks or leaks in the tube from the housing over to the reservoir, and that the tube extends far enough down into the reservoir that it is pulling only coolant back out. It is worth cleaning this reservoir, as there are a lot of solids that can build up and plug the end of the tube as it is sucking coolant back in- I preferred to not remove mine, so filled it with water and siphoned it out multiple times- amazing the crud in there.

Also make sure the aluminum lip ring inside the cap housing that the rubber disk in the end of the cap seals against is smooth, and does not have pitting or deposits that will keep the regulator from working. Once all of that is good (no more air under the cap), you can tell clearly if you have a slow leak because the level of coolant in the reservoir will be seen to slowly drop over multiple driving sessions. (A small amount is normal due to evaporation.)
 

Jk's97DSM

15+ Year Contributor
378
146
Apr 27, 2006
Norfolk, Virginia
Invest in a coolant pressure tester and a vacuum filler.
Pressure test the system. I put almost everything at 15PSI. It should hold solid. If it doesn’t there is a leak somewhere. Soapy water and whatever it needs until it holds.
There is also no need to burp a system when the vacuum filler has pulled all the air out. It should work every time if done right and the system holds pressure.
 

Mech Addict

Supporting Member
1,155
545
Jun 9, 2019
Jackson, Wyoming
Am I recalling correctly that you had a crack in your original radiator inlet? If so, how did you remedy that problem. New radiator, I presume. What kind? Or I might be confusing your car with someone else's. Hadn't seen you post for a while until this one.
 

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Am I recalling correctly that you had a crack in your original radiator inlet? If so, how did you remedy that problem. New radiator, I presume. What kind? Or I might be confusing your car with someone else's. Hadn't seen you post for a while until this one.
I got an aluminum one from RTM and it's held up well. Looks nice too.
 

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
I love those red lever "instant pressure relief" caps for my farm trucks, but I have weened myself off of them for my cars as they tend to encourage bad habits (opening system when hot) and are really not necessary if you do basic maintenance to keep the coolant system healthy.

In my experience, by topping off the coolant after you have driven it, by the 2nd or 3rd time you should have all of the air out of the main loop- the cap is the highest point in the system and air will collect there as it cycles. I also assume you are keeping the overflow reservoir at the full line. The standard coolant cap has a spring pressure regulator that maintains coolant pressure by burping over-pressure (excess coolant) out of the main loop into the overflow reservoir when it heats and expands, then a relief valve that allows coolant to be sucked back into the main loop from the reservoir when it cools and contracts again.

If the cap and reservoir are working properly, your system will naturally burp the air out on it's own and keep the main loop full and happy will little or no air under the cap by drawing in only coolant when it cools. Since you are seeing air in the main loop after several drive/cool cycles, I suspect the new cap may have a problem- either leaking too much coolant/pressure out into the reservoir and not maintaining the proper coolant pressure in the main loop, or more likely may be sucking in air or not sucking in coolant as the main loop cools.

Make sure there are no cracks or leaks in the tube from the housing over to the reservoir, and that the tube extends far enough down into the reservoir that it is pulling only coolant back out. It is worth cleaning this reservoir, as there are a lot of solids that can build up and plug the end of the tube as it is sucking coolant back in- I preferred to not remove mine, so filled it with water and siphoned it out multiple times- amazing the crud in there.

Also make sure the aluminum lip ring inside the cap housing that the rubber disk in the end of the cap seals against is smooth, and does not have pitting or deposits that will keep the regulator from working. Once all of that is good (no more air under the cap), you can tell clearly if you have a slow leak because the level of coolant in the reservoir will be seen to slowly drop over multiple driving sessions. (A small amount is normal due to evaporation.)
That's what ended up happening. I kept filling with concentrated coolant then distilled water, and eventually the coolant topped off just below the cap when cold. I also got the concentration up to where it needs to be, as temps can get below 0F here sometimes.

I'm glad I caught this in time as the ratio was rather low for some reason. I think I ran out of concentrate when I flushed the system to replace the radiator so it was less than 50/50. Now it's at a good level, in terms of ratio and actual coolant level, and all the air appears to have bled out.
 

XC92

Proven Member
1,478
321
Jul 22, 2020
Queens, New_York
Yeah investing in the coolant burp kit, the big funnel with the cap adapters is a good purchase. Usually you get more than just air bubbles coming out, you'll see dirt and contamination float up as well

You must be logged in to view this image or video.
I flushed the entire system earlier this year using coolant flush and a heater hose flush kit, so I'm good there. When I overhaul the intake, exhaust & turbo next spring, I'll clean things manually and replace any hoses that appear ready for replacement. Probably the last major task I need to get done in my overall restoration project.
 
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