Odd Coolant "Loss"

[g20ooh]

Hello CT,
If your still wondering.....I,d take a good hard look at the over flow bottle in the area just above where your coolant level stabilizes.What you are looking for is a pinhole- spidercrack- defective mold seam kinda thing that is probably very small and is temp. dependent.I've seen this more than once - last time it was the seam.Invariably it will be located where it is most difficult to observe so really checking the entire circumference may mean removing the bottle.I gather from your post that its near the top of the bottle. Sometimes you can trace down from the tube fitting.You're looking for white cloudy damage points as well.Many years ago I found one by pressurizing the tank(DO NOT DO THIS) while still hot by blowing thru a thin cloth directly into the bottle.Well I DID find the leak but I do have one exGF who probably stills wonders just what I really was doing to her truck one Saturday morning.

 

[ConfederateTyrant]

I have replaced the radiator cap with the Motorcraft replacement, topped off, and the level seems to stay at the top.

I am currently running an RMI-25 treatment to see if it finds any junk in my system. When I took ownership of the car, it had 88,000 miles on it, and when I "flushed" (I used the prestone power flush and followed the instructions there) at 89,000 miles, there were a good bit of rust colored deposits in the drained anti-freeze. I have flushed twice since then and the deposits are minimal, but I want to see if, and how well, the RMI-25 removes any more crud in the system.

Either way, the level has stayed at the top of the max level so far.

 

[va3ux]

Confederate,

I have exactly the same symptoms that you describe in your original post. Level stays put in the coolant tank for weeks, and then suddenly it seems to be down an inch or so. No external leaks, no smell, nothing at the weep hole, UOA shows no coolant. Top it up, the level seems to stay put again for weeks and eventually I notice it needs another few ounces of coolant again. Weird. I would say I add 3 or 4 ounces every 8 - 10 weeks.

I think I too will try replacing the coolant tank cap.

 

[ConfederateTyrant]

va3ux,
I kept my old radiator reservoir cap, incase the new one was not the correct one. I am going to get a mechanic friend of mine to pressure check the old cap next time I see him.