[JEEP97TJ]

First, let me say I've searched and gone through every TJ radiator problem/leak thread. They've helped to try and poinpoint the problem.

My Jeep's been running well for a while, seemingly without any issues. But over the past week that I've been home, the radiator fluid overflow bottle has been filled back up to the full mark (from about empty), yet today it is down and nearly empty. I realize that with the engine running, the overflow bottle may be more full than if the engine hadn't been running for a while. After parking the Jeep outside last night, I noticed two spots where radiator fluid had apparently been dripping. They weren't big, maybe 4-6 inches in diameter. At the bottom of the radiator, drips were forming on the petcock and another area or two from the same corner. It was not actually dripping.

Several months ago, I had the radiator flushed, and replaced the thermostat myself. There does not appear to be any leakage of coolant around the thermostat housing, though I need to check more closely. The coolant is collecting (in drops) on and around the petcock, I can see that the actual radiator fins in that lower corner look moist as if fluid had dripped down it.

Any suggestions of what may be the issue? I have no idea how I could lose a decent amount of coolant (say a liter or so from the overflow bottle) and not notice puddles under the Jeep. The Jeep has been in the garage, been driven daily the past few months, and there's no evidence of a major leak on the floor.

I am guessing that it must be leaking when I am driving, but don't know why. I have a feeling that a new radiator may be in order, but would like to narrow down the problem.

A possible culprit is the water pump, though that typically means coolant leaking down to the front of the oilpan and dripping from there. Not the case.

I checked all of the tubes going into the radiator, and all are tight and dry. The radiator itself is topped off with fluid, just the reservoir/overflow bottle that is low.

I checked the engine oil, and it is at the right level and in good condition.

Radiator cap is fine from what I can tell, seals nice and tight. Fluid level in the radiator itself is nice and full, reservoir at the "ADD" mark.

From what I've read up on, 4.0L TJ's radiators are comprised of a metal core, but plastic top/bottom, which are crimped onto the core. The seal can fail over time, and though it seems more common for the top seal to fail, in my case it seems to be the lower seal, since it appears that fluid is seeping around the joint of the metal/plastic.

I got the Jeep up to running temp, and let it idle while I checked things out, to see if having it warm and running would reveal signs of leaking. I couldn't find anything though. I also turned the heat on full blast for several minutes to determine if the heat running had anything to do with the coolant loss, but didn't seem to do anything.

Just trying to confirm this is a radiator problem, in which case I'll order a new one to install over winter break. I've read of the top seal of the radiator failing, but not much about the lower plastic/metal seal.

[Imped]

Hmmm, that's very strange. To help narrow it down, my water pump gasket (between water pump and engine block) was where my leak was coming from. It would leak down the pulley, onto the axle, tie rod, and drag link and form a little pool when running or still (faster when still). I know it's tough to see in there, but luckily it's not difficult to remove the fan shroud, undo the fan clutch, and get some breathing room in there so you can inspect the area. I would try that and see if that helps. Other than that, I can't be of anymore help.

[JEEP97TJ]

Originally Posted by imped4now

Hmmm, that's very strange. To help narrow it down, my water pump gasket (between water pump and engine block) was where my leak was coming from. It would leak down the pulley, onto the axle, tie rod, and drag link and form a little pool when running or still (faster when still). I know it's tough to see in there, but luckily it's not difficult to remove the fan shroud, undo the fan clutch, and get some breathing room in there so you can inspect the area. I would try that and see if that helps. Other than that, I can't be of anymore help.

I appreciate it. I'm fairly certain it is not the water pump. Everything around it was dry, and the drops of fluid are coming off of the radiator itself. Though I'll see how the leak may progress over the course of a week or so. The Jeep isn't being daily driven for the time being, so it could be tougher to tell what is about to fail.

Also, another question:

The stock radiator appears to be held in by some sort of metal bracket which is bolted to the back of the grille. The bracket has two tabs per side, one on top and one on bottom, which appear to be press fitted (seared into the plastic?) onto the top and bottom (plastic parts) of the radiator. On the passenger side, the two tabs have come loose from the bracket, so that side of the radiator has a bit of play and is tilted downwards a bit. Is it normal for this stock setup to fail in that way? Anybody have their radiator breaking free from it's bracket? It seems as if the brackets may have been heated up and seared into the top/bottom plastic parts of the radiator. Can anybody confirm this?

[crusher242]

Stare, and I mean STARE at the top of the radiator. It took me a while to figure out where my jeak was coming from, it was that damn plastic top. The seal is slowly going and it's pretty hard to figure out where it was coming from.

[gmiller0737]

See if you can rent a Radiator Pressure Tester from a parts store,With a pressure tester you will be able to pressurize the cooling system then look for leaks do not pressurize more than pressure of the stock cap.

[JEEP97TJ]

As for a new radiator, any suggestions of where to get a new one from? And from what I've gathered, it should be all metal, and a 2-row radiator. I've been recommended Radiator Warehouse, and have read on here about Radiator Barn. Anybody bought from them before?

[MysticGringo]

I had a similar mystery with my TJ the other day. Yesterday, I ended up flushing everything, backflushing the heater core, replacing some hoses, and replacing a new but poor quality water pump (had weak water flow with engine running). One of my symptoms was an empty overflow bottle after the engine cooled, but a really full one while the engine was hot.

We thought the issue might be with the radiator cap (but I wanted a full flush anyway, and discovered the weak water pump during that). A weak cap would over-fill the overflow bottle when the engine is working, causing it to dump some coolant out. Engine cools, and it sucks up the left-over. The little drips once you stop might be from where it splashed onto different places while moving. And, if your checking for leaks when its idling, you won't see it overflow the bottle, because the engine isn't under much load.

Ofcourse, I may not know what I am talking about, but its a cheap thing to change, and might be it.

[Varnish]

Originally Posted by JEEP97TJ

As for a new radiator, any suggestions of where to get a new one from? And from what I've gathered, it should be all metal, and a 2-row radiator. I've been recommended Radiator Warehouse, and have read on here about Radiator Barn. Anybody bought from them before?

I've bought two through radiatorbarn (for two different jeeps) and was happy with both purchases.

[motormark67]

Originally Posted by crusher242

Stare, and I mean STARE at the top of the radiator. It took me a while to figure out where my jeak was coming from, it was that damn plastic top. The seal is slowly going and it's pretty hard to figure out where it was coming from.

Mine leaks just like this, took me a while to figure out where it was comming from too. Funny thing is I don't think it leaks while it's running just after it sits, I just keep plenty of antifreeze handy and refill it until I can get a new radiatior; would like one of those aluminum radiators but kinda pricey.

[gcfishguy]

If you don't mind spending a small amount of $$ to diagnose it right.....call a local rad shop, ask them how much to supply a bottle of dye, then hit it with the black light.

Very small amount of flourescent dye (like 1oz or so)...you drop it into the coolant, drive it a day, then come back and they shine a hand-held black light in there, and anywhere the dye has leaked will glow like it's radioactive.

The dye is left behind even after the coolant evaporates or is burned off.

I can't see them charging very much to do that for you....

But...if the coolant's running down the fins, and pooling and dripping at the bottom, it sounds like you need a rad. Provided you verified all the hoses and connections, that's pretty much all it can be.

Forwards, you have just the rad and hose connections that can leak. If the leak was coming from behind the fan (waterpump, heater hoses, etc) the coolant wouldn't be collecting in the bottom corner of the rad.

I also had a similar leak on my ZJ. Rad looked fine, but when I got it out, it was only rotten in one place...on the engine side, in the bottom corner, where it's hidden behind the fan shroud. Also, I'm guessing that that's the corner that doesn't get a lot of coolant flow through it, and minimal air flow...so if any spot is going to retain road salt and moisture, it's that corner.

[JEEP97TJ]

Originally Posted by gcfishguy

I also had a similar leak on my ZJ. Rad looked fine, but when I got it out, it was only rotten in one place...on the engine side, in the bottom corner, where it's hidden behind the fan shroud. Also, I'm guessing that that's the corner that doesn't get a lot of coolant flow through it, and minimal air flow...so if any spot is going to retain road salt and moisture, it's that corner.

^pretty much describes it. Hidden by fan shroud, one corner, damp, etc.

Originally Posted by coolants

If Green Procurement is your goal we market SoyClean, Oil Gator and Micro-Nice, biobased solutions, Coolants, machining or grinding synthetic, semi-synthetic and soluble oil coolants. We also supply a range of complimentary products such as maintenance cleaners, absorbents and wiping cloths. If anything is an issue or not clear please send an email to richard@richcatt.com or visit our website http://www.coolantsandcleaners.com

Originally Posted by MysticGringo

I had a similar mystery with my TJ the other day. Yesterday, I ended up flushing everything, backflushing the heater core, replacing some hoses, and replacing a new but poor quality water pump (had weak water flow with engine running). One of my symptoms was an empty overflow bottle after the engine cooled, but a really full one while the engine was hot.

We thought the issue might be with the radiator cap (but I wanted a full flush anyway, and discovered the weak water pump during that). A weak cap would over-fill the overflow bottle when the engine is working, causing it to dump some coolant out. Engine cools, and it sucks up the left-over. The little drips once you stop might be from where it splashed onto different places while moving. And, if your checking for leaks when its idling, you won't see it overflow the bottle, because the engine isn't under much load.

Ofcourse, I may not know what I am talking about, but its a cheap thing to change, and might be it.

I will have to check that out more closely, compare coolant levels with the engine running and when cold. That might be it, though the water pump does not appear to be leaking.

How would you diagnose a weak cap? When I checked mine, it was nice and tight and appeared to seal well.

Originally Posted by Varnish

I've bought two through radiatorbarn (for two different jeeps) and was happy with both purchases.

I appreciate the info from everyone.

The Jeep will be driven around this weekend, so hopefully I will get an update on it's status.

[gcfishguy]

Originally Posted by JEEP97TJ

How would you diagnose a weak cap? When I checked mine, it was nice and tight and appeared to seal well.

Same dealy as for pressure testing the cooling system. Usually they're just a rad-cappinsh thing with a hose attached to a pump with a pressure gauge on it.
Screw it on in place of the cap and pump the system up to the correct pressure.

To test the cap, the testers usually have a double-ended sleeve . You put your cap on one end of the sleeve, and the pressure tester on the other.

That was years ago, though....they might be USB now. ;-) LOL

*Edited for speeling

[MysticGringo]

Originally Posted by JEEP97TJ

How would you diagnose a weak cap? When I checked mine, it was nice and tight and appeared to seal well.

I "tested" mine by replacing it, and see if I still had a problem. Its only $5, might as well replace it just to rule it out as an issue.

[JEEP97TJ]

I think I am going to go ahead and order a replacement (all metal) radiator since I doubt the stock one will last much longer anyway.

What else should I look into doing if I replace the radiator?

-Flush the rest of the coolant system (the block) ? How?
-Replace radiator hoses?
-Use hose clamps and not spring clamps on hoses
-Thermostat is new so I will leave that alone.

Anything else I should look into?

Also, what is one to do with an old stock radiator? Junkyard/dumpster? Obviously with the fluid properly disposed of.

For those that got the 2 row from radiator barn, does it come with a new radiator cap? Or should the stock one be re-used/new one purchased?

[gcfishguy]

Originally Posted by JEEP97TJ

What else should I look into doing if I replace the radiator?

-Flush the rest of the coolant system (the block) ? How?
-Replace radiator hoses?
-Use hose clamps and not spring clamps on hoses
-Thermostat is new so I will leave that alone.

Anything else I should look into?

Also, what is one to do with an old stock radiator? Junkyard/dumpster? Obviously with the fluid properly disposed of.

For those that got the 2 row from radiator barn, does it come with a new radiator cap? Or should the stock one be re-used/new one purchased?

It's hard to do a proper flush at home in the driveway. Just because it's hard to flush the block with new coolant, you'll either be left with a block full of old coolant, or if you use a hose to flush, fresh water.
If you know exactly how much fresh water is in there, you can add the correct amount of fresh coolant (not mixed) to end up with the correct mixture. See the problem?

If you wanted to do it right (and likely nobody would ever do this), take it to the shop, have a proper flush and fill, take it home, THEN change the rad.
Drain carefully and you'll only lose a liter or so of the new coolant, and the entire system will be flushed properly before you begin.
Leave the scrud in the bottom your drain bucket, top it off with a liter or so of new premixed coolant, off to the races.

If you haven't changed the hoses, or don't know when they were changed by the PO, change them. Well worth the money to know that they're new when you're a long ways from nowhere. If you pull the lower hose (usually the one that fails) you'll be able to tell if it needs replacement because the rubber will be all stretched and....floppy... Hard to explain, but you'll know it if you see it. But like I say, for the price of them, just do it.
The lower rad hose you buy may or may not have a spring in it. If not, transfer the spring from the old one. The lower rad hose has negative pressure (suction) in it sometimes and can flatten out and collapse without the spring in there.

Normally, rads won't come with a new cap on them. Again, for the price of a cap, put a new one on it. The cap maintains the pressure, and if it doesn't maintain pressure, the coolant will boil at a much lower temperature, resulting in you standing on your bumper, whizzing in your rad to get home. :-)

If the thermostat was just done, there's no need to change it.

If they're good quality spring clamps, they're actually better than hose clamps if you get big swings in temperatures. They hold well, and can expand and contract. Here, when it's real cold, you see cold leaks a lot. Start the vehicle at -35 and you get a small leak that stops one things start warming up.
Regular hose clamps are fine, though. And I'd sooner have a new hose clamp than a weak spring clamp.

When you're done, if the jeep will see freezing temps, make sure you check the freeze protection, or have it checked.
Checking it with an old style tester is okay if it shows you in the safe zone. If the antifreeze is too concentrated, the pointer will be way above the safe zone. A lot of people think that if the safe zone is good, then way above the safe zone is better. Not so...pure antifreeze will sent the pointer right to the top, and pure antifreeze will freeze at -5 F.
A good shop will have a gizmo that you put a drop of coolant on a lens and look through it. I want to call it a refractometer, but I'm pretty sure that's wrong...Anywat, those testers are dead accurate and measure the specific gravity by the way the light bends as it passes through the coolant.
There may be better testers out now, but I've been out of the trade for a while now too.

Sorry, long post, but your cooling system is serious business...Important when it's sitting there in the driveway at -40, and equally when it's working hard at +30. (100 degrees F) -40 is just -40, no matter how you measure it. :-)


As for the rad, flush it with water and put it at the side of the road in the spring if your community has a clean-up day thing. Once it's flushed out, it's just like any other scrap part...

And I might be putting my foot in it here, because I don;t even know for sure if it applies...it did on my ZJ and it was a pain.
If you have a factory tranny cooler, the line needs a special tool to disconnect it. Same tool as for the fuel line at the rail. It fits over the metal line and slides inside the fitting and pushes 4 barbs out of the way to allow the tube to slip out.
My ZJ had it, and if you have a auto trans, you might.