New overheating problem 87, 4.0, XJ

[CJR]

Ecomike,

I chased an intermittent heating problem on my 88XJ awhile back and it was a head gasket that would randomly leak. When cool, it would pressure test fine. On a hot day the head gasket would leak at random times. Finally, one day I saw a small puff of white smoke from my exhaust. The car was under warranty and the dealer replaced the head gasket and all was well. This was the same dealer who had pressure tested it numerous times and said the cooling system was fine.

I've incorporated 5-90's trick of drilling two holes, @ 12& 6 O'clock, in the thermostat and that purges my system constantly. In a turbulently flowing coolant, water pump impellers can occasionally create air gas-off from the coolant (i.e. bubbles) or cavitate (i.e. system pressure equals vapor pressure at some point in the coolant). This may occur momentarily at some RPM. Once the air bubbles form, it takes awhile for them to be reabsorbed by the coolant. So anything that constantly purges the cooling system, like 5-90's trick, is good in my view.

Good luck!

Best regards,

CJR

 

[Ecomike]

I am really hoping mine is not the head gasket. It is running hotter for sure, so it is either running leaner or the thermostat is not opening fully as it is about 30 F hotter at the Thermostat housing.

The problem was a sudden change, nothing gradual about it, so I doubt it is the radiator or the clutch, which are only 3-4 years old, and only have about 30,000 miles of mild use on them.

No signs of leaks, and the pressure is way up there, hoses are rock hard! I am planing to swap the thermostat and clutch in the morning, and I may pull the plugs to have a look see. I may break down and try the extra hole in the thermostat.

I am also going back to a 160 F Thermo for now. Lastly I am going to add some fresh brown head gasket sealer pellets to the coolant right away, since I replaced the coolant that blew out when the lower hose came off, and I lost any that I had in their from the prior fill up.

I still need someone to collect and post some intake manifold temps here on a non-overheating Renix jeep! PLEASE!

Ecomike,

I chased an intermittent heating problem on my 88XJ awhile back and it was a head gasket that would randomly leak. When cool, it would pressure test fine. On a hot day the head gasket would leak at random times. Finally, one day I saw a small puff of white smoke from my exhaust. The car was under warranty and the dealer replaced the head gasket and all was well. This was the same dealer who had pressure tested it numerous times and said the cooling system was fine.

I've incorporated 5-90's trick of drilling two holes, @ 12& 6 O'clock, in the thermostat and that purges my system constantly. In a turbulently flowing coolant, water pump impellers can occasionally create air gas-off from the coolant (i.e. bubbles) or cavitate (i.e. system pressure equals vapor pressure at some point in the coolant). This may occur momentarily at some RPM. Once the air bubbles form, it takes awhile for them to be reabsorbed by the coolant. So anything that constantly purges the cooling system, like 5-90's trick, is good in my view.

Good luck!

Best regards,

CJR

 

[Ecomike]

I ran the standard 2 minute bubbler, head gasket leak test on mine, ran it for 20 minutes to be sure. It is not a head gasket leak.

I installed the heavy duty 97 ZJ fan clutch, which helped some.

I have a new 3 row CSF radiator on order, on its way. I am also upgrading the AC condenser to a newer style, true parallel flow style condenser for R-134a, and I am installing an inline filler assy with a radiator cap on the upper radiator hose so I an bleed air easier, and so I can use a standard radiator and Rcap tester on the rig. I will also install the after market cap that has the pressure/temperature read out in the cap.

I have not decided what I will do with the overflow line in the neck. Or the poly pressure bottle. That will depend on how these mods work out.

 

[Ecomike]

Well I cranked the 87 Renix beast up today. To update, I installed a new water pump a short while ago, did not help, new thermostat was also no help, a new ZJ clutch helped some but not enough.

Today I started it up after installing a 97 AC parallel flow AC condenser (R-134a upgrade done 18 months ago). Also installed a 3 row all copper/ brass CSF (The real McCoy folks) radiator. I had also installed a Jugs in line filler neck in the upper radiator hose, currently with a 16 psi cap. New Renix POS bottle with a new 20 psi Volvo style cap by Stant on the bottle.

Got about 1.7 gallons into the cooling system, cranked her up. Let it run about 45 minutes while charging the AC system.

Most notable thing I noticed was that the right side (drivers side) of the radiator tank had a huge temperature gradient on the outlet tank from top to bottom. 120 F at the top and 190 F at the bottom. The thermostat housing was reading 220 F.

The AC condenser was 135 F everywhere (still charging so not real hot yet).
After scratching my head a while it dawned on what I was seeing.

Anyone know what causes this? (Besides me that is)

 

[winterbeater]

Automatic tranny fluid not heated up yet?

 

[Ecomike]

Automatic tranny fluid not heated up yet?

Nope.Tranny is in park.

Try again. Come on guys, you can do better than this! LOL.

Second hint, it is not trapped air in the engine.

 

[menos]

Wrong rotation on the water pump you installed recently?

 

[bluejeepkid]

heater hoses on the tstat backwards?

 

[Ecomike]

No, no and no.

I mentioned it several years ago in an old thread. Anyway, the reason it is progressively colder at the top side is that the radiator has air trapped in the top side, which in my opinion is the biggest problem with the Renix OEM plumbing after replacing parts.

The water pump hose the radiator is connected to is at the bottom of the radiator. Water (coolant) is heavy than air so the air gets trapped in the top of the radiator, possibly for days or weeks unless you get rid of it some other way. I have yet to bleed my inline filler neck on the inlet hose to the radiator that I have added to my set up.

In spite of the trapped air (I got some out by racing the engine periodically and topping off the renix bottle for 2 hours, but it is still about 1/3 air at the top of the new radiator) in the top half of the radiator, and resulting loss of cooling efficiency, my new set up is running noticeably cooler. The 3 row brass / copper CSF radiator and the 97 year, parallel flow style AC condenser on the AC I upgraded to have both helped. I will post up final test data later once I get all the air out of the radiator. For now it ran at 185 F at the thermo housing during my final readings with ambient at 88 F, no AC. AC was still charging during earlier AC test, but it ran about 200 F at the thermo housing at idle with air in the radiator (1/3) and only 14 oz of R-134a added from a vacuumed out system! And I was already getting 50 F air out the AC vents, and 40 / 225 PSI on the gauges, on Max AC (Jeep doors shut), with 88 F ambient.

 

[Electrichorseman]

Make sure the cooling system is full when cool. Then remove the temp senson (top of engine by firewall). Coolent should leak out. This is an area in the engine where air can get trapped.

 

[Electrichorseman]

"Wrong rotation on the water pump you installed recently?"

That happened to e once. The DEALER parts guy gave me a pump for a six cylinder when I asked for a 4 cylinder.

Drove me nuts. However it caused major overheating within a few minutes! Doesn't sound like his problem.

Maybe it had something to do with stopping to look at the Grand Cherokee! They're very sensitive you know.

 

[Ecomike]

Make sure the cooling system is full when cool. Then remove the temp senson (top of engine by firewall). Coolent should leak out. This is an area in the engine where air can get trapped.

Did you bother to read the entire thread here? I think not!

:twak:

The way the Renix coolant system is built and designed, it traps air in the radiator, far more air, and far more problematic that any air trapped in the block.

Last night I got most of the air out of the radiator by using the filler neck / standard radiator cap on the filler neck that I had installed in the upper radiator hose, in an elevated position, while also opening the POS plastic bottle cap. Doing this twice between cool downs, got me from a a half full of coolant radiator, to a 90 to 95% full of coolant radiator (maybe 100%, not ready to claim todal success). But the temperature profile on the right side tank of the radiator looks like I have 90-95+ % of the air out now.

Operating temperatures are lower now, and the temperature profile on the radiator right side tank looks like the radiator is mostly air free now.

 

[Electrichorseman]

I was comenting on somebody elses post.

 

[Ecomike]

I was comenting on somebody elses post.

Sorry, , then. Might help if you quote the person who you are commenting to next time.

 

[winterbeater]

Well I cranked the 87 Renix beast up today. To update, I installed a new water pump a short while ago, did not help, new thermostat was also no help, a new ZJ clutch helped some but not enough.

Today I started it up after installing a 97 AC parallel flow AC condenser (R-134a upgrade done 18 months ago). Also installed a 3 row all copper/ brass CSF (The real McCoy folks) radiator. I had also installed a Jugs in line filler neck in the upper radiator hose, currently with a 16 psi cap. New Renix POS bottle with a new 20 psi Volvo style cap by Stant on the bottle.

Got about 1.7 gallons into the cooling system, cranked her up. Let it run about 45 minutes while charging the AC system.

Most notable thing I noticed was that the right side (drivers side) of the radiator tank had a huge temperature gradient on the outlet tank from top to bottom. 120 F at the top and 190 F at the bottom. The thermostat housing was reading 220 F.

The AC condenser was 135 F everywhere (still charging so not real hot yet).
After scratching my head a while it dawned on what I was seeing.

Anyone know what causes this? (Besides me that is)

OK. That one was too easy to even guess. That's almost like: My XJ quit running, what's wrong? I'm out of gas.

So, how does the AC work with the new condenser? Never mind.

 

[Ecomike]

More details on the condenser upgrade are posted in the other thread, but briefly, upgrading to a 1997 parallel flow XJ condenser got my AC pressure with R-134a down from 330 psi (at 100 F ambient) to 215 psi (at 90 F ambient), and my vent temps down from about 65 to about 45 F. Major improvement. It has not 100 F yet, to get a direct comparison, but I doubt it will go over 240 psi, and 50 F at the vent on the 100 F ambient days.

 

[Ecomike]

OK. That one was too easy to even guess. That's almost like: My XJ quit running, what's wrong? I'm out of gas.

Exactly, it's like trying to cool coolant in a radiator without ever putting the coolant in the radiator.

As in, did you plug the computer in? LOL.

 

[Ecomike]

Final tests were all successful. AC works better than ever. Ran at 200-207 F today at the thermostat housing, on a 95 F ambient day, 66 mile round trips (last 2 days), with AC on Max.

Final changes, installed a new 97 model AC parallel flow condenser, a CFS brand 3 row copper / brass radiator, a ZJ fan clutch, (new water pump 3 months ago with a 180 F T-stat), new Renix bottle with a Stant brand Volvo bottle cap (20 psi rated) on the POS plastic bottle, and JAQ inline filler neck with a 16 lb radiator cap on the radiator inlet hose.

The system never got over about 8-9 PSI all day. The radiator style cap has never opened, as I predicted!

 

[1990JEEPXJ]

why didnt you just go with an open system? just curious as it seems to be an easy effective mod.

 

[Ecomike]

why didnt you just go with an open system? just curious as it seems to be an easy effective mod.

I don't like the pressures that an open system operates at. It depends on the radiator cap to vent excess pressure and vacuum daily. With an open system the radiator, hoses and heater core see 16 lbs of pressure almost immediately, and continuously after that as the coolant warms up as liquid is not compressible. My best guess is the radiator caps on an open system start to vent at 16 lbs at around 160 to 170 F, if not sooner.

The Renix system has to get up to about 265 F for the system to reach anything close to 16 psi, as the air in the bottle is compressible. In fact the Renix system does not vent at all, not even air with a properly working cap, contrary to what I and others have said in the past, it is a true closed system.

There is a distinct advantage to lower pressure, and an advantage to not having the coolant exposed to air and CO2 as you get with an open system. The coolant stays cleaner.