Real strange backwards radiator problem

I have have had an unusual radiator problem for the last four years. :bawl:By backwards, I mean most radiator problems have to do with leaks. Mine does not leak, and to be a little punny it does not suck either, and that sorta sucks if know what I mean. In other words it refuses to refill itself from the overflow bottle when it cools down overnight.

I had the radiator cleaned, rodded out, and repaired recently, 3 weeks ago and the unusual problem did not go away.

The system works normally and runs fairly cool while the engine is running (170 winter, 215 summer with A/C on at 100 F ambient). It is an open system with an overflow bottle. The problem I have is that the coolant in the overflow bottle, about 80% of the time, refuses to return the radiator when the radiator cools down overnight. Sometimes it has returned to the radiator in the past, like 20% of the time, but since I got the radiator rebuilt it has not returned on its own, yet.

There are no external leaks anywhere and have not been any for 3 years ( I would have noticed). The radiator had a small head leak at the top of the radiator that sealed itself (good use of radiator sealant) but that got properly soldered at the radiator shop a few weeks ago, so it is no longer a possible source of air getting into the radiator during cooldown.

The overflow bottle and return hose is air tight, no fluid or air leaks, the radiator cap has been replaced and tested with several brands and pressures over the last three years (tried like 5 new caps). The overflow nipple on the radiator cap throat is OK. I have put 20,000 miles on this beast while I had this problem. I just manually poured the coolant back into the radiator each morning if the coolant bottle was full. The engine/radoitor system runs cool. The overflow quantity is normal.

I have run out of ideas. Any one else ever had this sort of problem and found a solution, or figured out what was causing it.

I thought it might be something like a water pump seal going out, but its been doing this for 20,000 miles since 2003!

Its a 1985 jeep radiator (was 2.5 Liter gaser) in a jeep Cherooke Pioneer , now with a Nissan SD22 diesel transplanted engine with a manual tranny so no tranny fluid in the radiator. Absolutely no engine problems and no coolant/oil mixing, etc. Everthing is normal except this da#n coolant return problem. Oh, and all the coolant hoses are only 12 to 18 months old. I am currently running a 13 Lb. pressure cap and the overflow that does not return to the radiator is about 1 quart.

So what's my problem????:helpme:

Does the radiator make a sucking sound when you open the cap? Could the hoses be collapsing and relieving the vacuum that would pull the fresh fluid back in?

How about a leak at the neck the cap mounts on, either the top seal on the cap doesn't seal, maybe a pin hole in the neck or a bad join for the recovery tube to the neck?

I was gonna say radiator cap but you've already tried several, so that's not the problem. How about the hose going to the overflow bottle (if you haven't changed it)? Any cracks or loose connections? And lastly how about the overflow bottle itself? Any cracks that could be sucking air in instead of coolant from the bottom of the bottle?

Kyung

Rick Anderson said:

Does the radiator make a sucking sound when you open the cap? Could the hoses be collapsing and relieving the vacuum that would pull the fresh fluid back in?

How about a leak at the neck the cap mounts on, either the top seal on the cap doesn't seal, maybe a pin hole in the neck or a bad join for the recovery tube to the neck?

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I have on occasion heard the vacuum release when opening the cap first thing in the morning, so yes there was some vacuum in the radiator. It was not a lot of vacuum, probably the residual caused by the spring (2 lb?) in the cap itself.

I tried tightening up the clamps on the return/overflow hose and I may just replace the clamps and the hose next. It is currently nylon/ soft clear plastic, I will try vaccum rubber tubing next. The neck is in great shape, but I have not looked under the bottom side of the thin overflow neck/tube for a tiny vacuum leak. Also it is covered with tubing so not readily visible. But it all looked good to go when I got it back from the radiator repair shop. Should have checked it (the neck) with a magnifying glass I guess.

It's got to be somewhere in that neck seal tube, tubing area. Just gotta find the bloddy leak. Time for my microscope I guess.:laugh:

The thing I keep thinking is a vacuum leak would also be a coolant leak, but I guess in that overflow neck tubing area it just shows up as a slow tiny vacuum leak, and no visible coolant leak, unlike the pressurized part of the coolant system.

ive had it where the sealing surface on the neck wasnt perfect and the vacume leaked out of the top seal. no coolant loss just a very small vacume leak. I double gasketed it and fixed the problem. might be worth a try

dzraces said:

ive had it where the sealing surface on the neck wasnt perfect and the vacume leaked out of the top seal. no coolant loss just a very small vacume leak. I double gasketed it and fixed the problem. might be worth a try

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Thats what I was getting at, the bottom seal is what holds the coolant in the system, the top seal is what seals the vacuum to return coolant as the system cools. A leak at that surface or the neck could lose the vacuum that is needed to draw back fluid into the system.

Don't know if the 3lb difference would be an issue, the recommended psi on the cap is supposed to be 16lbs not 13lbs. At 13lbs it may push more coolant into the overlfow than it's supposed to and stop pulling it back in like it's supposed to.

RichP said:

Don't know if the 3lb difference would be an issue, the recommended psi on the cap is supposed to be 16lbs not 13lbs. At 13lbs it may push more coolant into the overlfow than it's supposed to and stop pulling it back in like it's supposed to.

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The Nissan FSM for the SD22 deisel engine I am using calls for 13 lb cap, so that is what I am using. It is a cool running engine, 2.2 liter four banger that replaced the 2.5 liter OEM gaser.

The coolant bottle is about 1 quart, and the overflow is only running 1 pint into the bottle at peak operating temperature (A/C on, Idling in 100 F traffic for an hour) from an initially cold, full system, meaning radiator and engine are full and burped. Don't have the typical jeep air bubble problem and air purge problem that we have with the 4.0s.

Have you checked the overflow hose itself, to make sure there isn't some crud or obstruction in it? The vacuum in the radiator is pretty weak, and it might well still be able to pas the fluid out under pressure, but not back in. Make sure the overflow bottle's vent is free too.