Remove the radiator cap when the engine is cold.
Make sure the radiator is full.
Pour a teaspoon of ground black pepper into the radiator and reinstall the cap.
Start the engine and let idle until until coolant leak stops.
That’ll buy you some time so you can decide what to do.
Tester
Thanks for the tip!
Thanks for all the help, Tester! So the black pepper acts like a stop leak?
I drove a Beretta for over a year with an external head gasket leak. And black pepper allowed that. Until the head gasket failed where no stop-leak product was going to stop it.
Tester
Retorquing the head bolts might help. It worked on my 1984 Chevy Cavalier that had an external head gasket leak - although that may have been oil, which probably has less pressure behind it, compared to coolant,
Good luck and please keep us informed.
You can’t retorque the head bolts on this engine as it has torque-to-yield head bolts.
If you do, the head bolts will lose their clamping force, and the head gasket will leak everywhere.
Tester
Good to know. Thank you.
OK, the plot thickens! This morning I filled the radiator and overflow tank with coolant and it took a lot – maybe 2-3 quarts of coolant or so.
Since then the car has been running fine at the right temps on a few short trips I took. Also, AC is back working fine again.
I took it to a local shop and they did a pressure test on the coolant system. They could not find a leak. Their theory is the thermostat is bad and pressure was building up in the overflow tank and that’s how I lost all the coolant.
After taking it for a drive after getting it from the shop, I checked the coolant again, and this time it was filled to the brim in the overflow tank (even though this morning I filled it to the F line in the tank, which is a couple inches lower) and in fact coolant was seeping out from the overflow tank cap (engine was still hot).
I also checked that little oval pool of liquid that I took a photo of above, next to the alternator, and that does seem to be liquidy and does seem to have a slight green/yellow tint (the coolant color), but the engine is dirty, so it is likely mixed with oil and hard to tell the true color.
I did notice that the overflow spigot on the coolant overflow tank cap was pointing in that direction, so maybe that is how that little pool of coolant got there?
Anyone have ideas on what to do or check next? I’ll keep an eye on the coolant level. In the past I’d just check and refill the overflow tank, but now I know I have to keep an eye on the level in the radiator as well.
I would investigate for head gasket leak. A hydrocarbon sniffer held over the open radiator while the engine is warm and running may detect exhaust gasses there. (See George’s advice in post #4, to look for bubbles coming up at the radiator neck - those are probably exhaust gas); also there are chemical test strips that detect exhaust gases in coolant.
These are the fairly simple ways to test for a bad head gasket, or worse: cracked cylinder head. With a 6 you have 2 heads, and it will take more to figure out which, if either, is bad.
At this point I think your original idea to replace the thermostat makes sense. Years ago I had a thermostat that failed in a way where it would stick closed, caused overheating, then all of a sudden it would unstick, accompanied by a noticeable “click” and a “rushing” sound, presumably the coolant moving rapidly through the hot engine. No more overheating for a while, then a few days later it would stick shut again. Suggest to remove the thermostat, put it in a pan of water on the stove and heat it up, watching it open while monitoring the water temperature with a thermometer. Do the same test with the replacement thermostat for comparison.
Why not just install a new thermostat and forget all that?
Tester
Thanks for the tip. Earlier I cleaned up that wet spot (which I thought could be coolant) next to the alternator in the middle of the photo above, and since then I’ve driven it for probably a half hour. No other wet spots have accumulated. My overflow tank is a little moist on top, but it’s stayed filled at about 1 inch above the fill line, while the engine is still warm. This morning while cold, I filled it to the fill line.
Also the engine temp gauge has stayed where it should, in the middle between H and C.
What if the new thermostat doesn’t solve the problem? How would OP know the new thermostat wasn’t faulty out of the box?
Yeah, I’ll probably install a new thermostat this weekend. do you think a new radiator cap would also help? If it’s bad and not opening as it should, couldn’t that lead to over pressurization and resulting coolant loss?
Sounds like I’m possibly having the same problem as you did.
When you’re having a cooling system problem, you replace the easy/cheap stuff first.
But in your original post, you stated that there may be a coolant leak in the area of the head gasket.
And if that’s true, you want to stop that leak.
Tester
Ask your shop if they tested the cap as part of the cooling system pressure test. Usually that’s part of that job.
I’ve seen a bad radiator cap keep the system from pressurizing.
Then coolant boils after shutting the engine off, causing the reservoir tank to spill.
You can squeeze the radiator hose as the engine warms up as a rough pressure check.
It should get real stiff after a couple minutes.
Thanks, that’s a really good tip. Now my plan is to replace both the radiator cap and thermostat. Also, car has been running fine the last couple days on short trips and the temp is staying in the normal range.
I would like to know what exactly is the proper procedure for “retorquing” head bolts on any engine. This was something that I had discussed in the past, and was told to buy a new set of bolts, go through the loosening sequence, removing one at a time, replacing it with a new bolt, then completing all three tightening steps on that bolt, and proceeding down the sequence. I am just curious if this is the correct method if bolt tension loss is suspected.