Closed Loop problems

I am out of ideas.

I get an almost free 88 2 door, PO says it has a blown head gasket(warped head) So I pull the head, yup its warped, get it rebuilt, valves etc. Put it all back in with a new waterpump, Tstat, tstat housing(so I can run an electric gauge), fan clutch, radiator is fairly new, PO didn't know how old, but its not rusty, clogged etc.

The water pump and Tstat are working properly, the jeep runs perfect, nice and smooth good power etc. I have driven it a few times with a new head, runs perfect except when it warms up it empties the coolant.

The coolant is coming from the coolant bottle cap(It is a brand new cap) but only after it gets warm. You can feel the coolant going through the radiator as it warms up. The flow feels good, tried bleeding both at the new TStat housing and the temp gauge in the back. Drilled the hole in the TStat, I am pretty sure there is no air in the system.

These temps are all with an IR temp gauge:
Tstat out to radiator 200
Inlet side of radiator 180
Outlet side of radiator 110
Hose to heater core 210

Makes me think it is cooling fine, once the coolant starts to leak out though is when it gets real hot real quick.


With those temps, I am loosing all my coolant out of a new radiator cap. It worries me that I am have another headgasket leak that is pressurizing the coolant system. But it doesn't start leaking untill its warmed up. Then when I shut it off, the coolant in the bottle is will buble a few times. There is no oil in the water or water in the oil that I can tell. Its all new coolant and water.

I am out of ideas, the jeep runs so good, should I try a new coolant bottle, its not cracked it just pushing out around the brand new cap. Should there be that much pressure in the system?

I would get a new bottle. I have a 88 as well, and had the same problem. I replaced both the bottle and cap, which solved the problem. Since I replaced both at the same time, I don't know which one (if not both) was the culprit for the leak. The old bottle was quite hard and brittle, but with no visible cracks.

Closed loop systems are under a naturally high pressure, don't worry about that.Just replace the bottle and it should be fine, it's usually the first thing to go as far as I know.

If you can, keep the closed loop system running well, it's supposedly more efficient than an open loop.

Happend to me all of the time when I had an '87. I had a stripped out cap that would hold pressure with just the right conditions otherwise it would dump a bunch of coolant when I shut off the engine. New bottle with cap was about $45 and 30 minutes to swap out. Never had a problem again.

Try a worm gear clamp on the bottle cap first. If it still leaks get a new bottle and cap. They are about $25, Ebay has them, and several of our sponsors have them. Even the new ones benefit from a worm gear clamp on the bottle cap. Search for "Renix Bottle clamp" to see the thread on this.

Now, about the radiator, 110 F on the radiator outlet with a 180 F inlet tells me the radiator has poor flow due to blockage, or the water pump is toast. The temp drop across the radiator should be about 30 to 40 F, and the 30 F difference from the radiator inlet to the heater hose is another dead give away that the flow through the radiator is partially blocked.

My radiator had large hot and cold spots in the core when it did the same thing.

You have not over filled the bottle have you? It should be no more than half full at room temperature.

Nope the bottle is about half full, as the engine warms up the coolant will get higher and higher in the bottle untill it is leaking out.

I will probably just go right to a macs metal bottle. I would really like this to be reliable when it is 110 and run it with the AC on. I am not opposed to aTaurus fan or even a new radiator to help down the road. Once I get the bottle I will be able to let it get very warm and figure out what is going on with the radiator. Those temps were pretty soon after the Tstat opened and the coolant started flowing through. I couldn't leave it running because of the coolant pouring out from the bottle cap. I am sure a pressurized system will help with the cooling efficiency through the radiator.

thanks for all the help.

From the sound of that you had a bad cap on the bottle for sure, or the engine is pressurizing the coolant system, i.e. cracked block or leaking head gasket still. Mine only rises about 1/2" at most in the plastic bottle from 100 F to 235 F (based on temp readings I got with my IR). A bad cap will make it over heat very quickly.

Did you buy and use new head bolts???!!!!!!

Did you have the top of the block checked for flatness?

The bottle caps are notorious for expanding as they get hot, which loosens the threads, leading to loss of cap seal, bingo loss of cooling system pressure, etc. The worm gear clamp eliminates that problem, it keeps the plastic caps sides from expanding.

I am also sure you have a radiator, and or water pump issue. My money is on a blocked radiator, and a bad bottle cap (that needs a clamp to work properly for more than a few weeks in this weather), both indicated by the data you posted.

Things happen slowly around here.

So I tried the worm clamp on the bottle cap, still leaked. Got a Macs metal bottle, didn't leak but still overheated.

So I ordered a CSF radiator from DPG. He didn't have any closed loop radiators so I decided to convert the system. I have a new 3 core all metal radiator. converted hoses with a new heater valve. I have 2 temp gauges, 1 is in the Tstat housing(aftermarket) and then the stock in the back of the block. I finally got a real drive on it today. It was about 105 today, with the AC on to run the aux fan that I haven't rewired yet.

On the stock temp sensor(back of the block) it never got over 200. On the aftermarket sensor in the Tstat housing it was 240.

Is this normal? It is running great, it will warm up on the freeway an cool off when I coast so I think the radiator is working. It's just that 240 temp is scaring me.

On another note, how in the world do you tighten the exhaust manifold bolt in the middle that is impossible to reach. After doing the head I though it was tight, but a small leak has shown up. I there something obvious that I am missing?

You need to figure which gauge and sensor is giving you accurate temperatures. Not unusual for the thermostat temp to be higher that the rear head sensor temp by a good 20 F or so, but 240 F, is that is accurate is too high. What is it after a few seconds at 2000 rpm, versus extended idle now.

If you remove the airbox, you should be able to get to that middle bolt with some extensions.

FYI if you really want to lay your head gasket fears to rest, I'm pretty sure there is an additive/tracer you can find in various stores that you put in your coolant. It'll turn the coolant an unusual color if exhaust gases find their way into your coolant, I believe it actually detects the elevated levels of dissolved carbon dioxide (which produces carbonic acid in solution) resulting from the exhaust gases but I'm not sure.

It does sound more like a bottle/cap problem though.

EDIT: it's not an additive, it's something called a "block tester" you can buy for approx 45 dollars. You put some tester fluid in it and then suck up some coolant and if the tester fluid changes from blue to another color, you have a leak. Just found via google.

kastein said:

FYI if you really want to lay your head gasket fears to rest, I'm pretty sure there is an additive/tracer you can find in various stores that you put in your coolant. It'll turn the coolant an unusual color if exhaust gases find their way into your coolant, I believe it actually detects the elevated levels of dissolved carbon dioxide (which produces carbonic acid in solution) resulting from the exhaust gases but I'm not sure.

It does sound more like a bottle/cap problem though.

EDIT: it's not an additive, it's something called a "block tester" you can buy for approx 45 dollars. You put some tester fluid in it and then suck up some coolant and if the tester fluid changes from blue to another color, you have a leak. Just found via google.

Click to expand...

Block tester is a free rental (just make a return deposit) at places like AZ, AA, and O'R parts stores, and buy the bottle of test fluid, $7, not refundable. The test fluid changes color in a bubbler, it does not go into the coolant, or change coolant color.

I don't think he has much of a problem left, if any. He is in Arizona, hot, 105 F and the read head is reading 200 F with the AC running. I bet if he checks the thermostat at 2000 rpm, he is at about 210 to 220 F at the T-stat with more water flowing.

I also suspect his 240 F reading is off. get an IR temp tester and double check it.