Standard over heating problem

I recently lucked into an '89 XJ for dirt cheap. The previous owner told me that the engine needed replacing. I jumped the dead battery and it ran just fine, until the coolant begin "boiling" over. I've read most of the forums info on this and think I have a pretty good grasp on the problem. I had a mechanic replace the fan clutch and he used a vacuum system to refill the coolant into the system. This seamed to work for about a week but then it began bubbling over and overheating. I'm worried the head gasket may be bad but when the mech used the vacuum system, we let it sit for about 5 minutes and did not notice a drop in the vacuum pressure so we assumed there were no leaks. Could the defect in the head gasket be small enough to not be noticed in a vacuum but when exhaust pressue is applied, it leaks into the cooling system? I replaced the thermostat with a Checker Auto one, but was not familiar with the breather hole and may have installed it wrong. I am going to get an OEM one and install it soon. Also, I plan on replacing the "closed" system with an "open" system. Will there still be a problem with the cooling system if there is a defect with the head gasket but I update the radiator first? This is a budget spare Jeep and I can only do a little at a time.

Thanks,

dgoxj

I would suggest a radiator cap and thermostat from the dealer. Also, could it be that the radiator either needs a good cleaning or replacing.

Also, what do you mean by boiling out? Out of what? the radiator?

The whole cooling system may need cleaning as well.

Also, if you have a blown head gasket - as others have suggested before, check for water in the oil. Have you done a compression check?

Tom Dennis

The cap itself is a weak spot. It can look all right, but have a leaky rubber gasket, and that can be enough to put you over the top. Try running it for a while, then shut it down and let it sit for a while to cool. When you crack the cap, it should still give an audible hiss. If not, suspect the cap. Take a good look too at the radiator itself. At that age, the fins can start to corrode out, and even if they're still present, they won't make good thermal contact with the tubes. If you see gaps or holes in the fins, suspect fin rot. A radiator with bad fins will never cool properly.

I would suggest...

first to drain the system, replace the thermostat with OEM and refill with water and add a bottle of prestone super flush, the kind that tells you to run it for 7 hours of normal operation. Then I would install one of the prestone back flush kits, it has a 'T' fitting that goes on one of the heater hoses. Drive it per instructions then back flush it, the purpose of this flushing is not to get the rad cleaned out but clean out the heater core and the engine itself. Then I would do the following, I would not even think twice about it, just throw in a new radiator, new hoses, new thermostat, either replace the plastic pressure bottle and cap with OEM or get the aluminum one from summit that takes a normal radiator cap, that costs more up front but is less of a PIA in the long run.
When the fins on the radiator start to 'rot' you can run a thumbnail gently along them just enough to deflect them a bit, if they are good they will spring backup, bad they will stay bent.
When removing the hoses don't pull them off, gently slice them with a razor knife or exacto knife, be careful of the plastic fittings, might want to have a new mixing valve on hand when you do this, cheap insurance if the exisiting one falls apart while replacing hoses and several here have had that happen.

I concur with Matthew and Rich. An '89 XJ radiator is going on artificial life support at this point. I don't think you have a head gasket problem, I think you have a radiator problem. The OEM heavy duty radiator on my '88 sprung a leak late in 1999, so you're on borrowed time.

If you feel you simply must convert to the open system, you might as well do it when you buy the radiator. Just remember that you WILL then have the problem of finding a way to control the auxiliary fan. The open system does not cool any better than the closed system, so personally I cannot find any way to justify the headaches of dealing with the fan issue. Quadratec has the plastic pressure bottles for $20, so that's less than you'd spend mucking around with alternate ways to control the fan. Of course, the Moroso aluminum tank is far better, but it also costs 4 times as much as the plastic bottle from Quadratec.

Why is the aluminum radiator better than copper. Does it stand up to corrosion better than copper? It would not be for cooling efficiency as copper is better.

Tom Dennis

Anthropy said:

Why is the aluminum radiator better than copper. Does it stand up to corrosion better than copper? It would not be for cooling efficiency as copper is better.

Tom Dennis

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Who said aluminum is better than copper? Cerrainly not me. The OEM radiators are aluminum and that's part of the reason they plug up with corrosion so fast, as well as why they rot out in half the time old copper/brass radiators used to. And you are correct -- copper is a better conductor of heat than aluminum.

The factory uses aluminum and plastic to save weight.

By "boiling over" I mean that coolant is bubbling out of the pressure bottle a lot, like big mess. There is no perssure sound when I remove the cap so I am begining to suspect the cap. I forgot to mention that when I purchased the Jeep, the previous owner claimed to have installed a new radiator. My mech confirmed that it appeared to be a new radiator, including the previous mech not re-installing half the bolts that hold the readiator in. I think I will install an OEM thermostatand new cap and try that. If it works I will probably began replacing the hoses and other equipment and leave the closed system in place.

Thanks for all the advice, I've always dreamed of owning an XJ since my family grew out of my '63 CJ5 and I won't let minor design flaws discourage me.

dgoxj

A word of caution -- the reason the cap doesn't seal is probably as much due to deformation of the bottle as to the cap. People have posted here in the past that installing a new cap on an old bottle often doesn't work. With Quadratec selling the complete bottle and cap for $20, IMHO it doesn't make sense NOT to replace the whole shebang.

Yes, with an XJ that old I would renew the entire cooling system for no other reason that it 14 + years old. The cooling system is too important to mess with.

In the real world I would use a brass radiator. First off it been shown to work in thousands of XJs on the road with stock engines. Remember AMC & Chrysler had to warranty the vehicle with what ever radiator installed, so they had to take in all operating conditions for design to minimize warranty pay out.

Another reason to use a brass radiator is because of the low corrosion. Basically brass is pretty neutral to corrosion.

I have had multiple classes in corrosion prevention, at college and short courses at work. They get into the anode/cathode and how certain metals will corrode for other metals. The Natural gas companies use magnesium blocks connected to their gas lines with wires. The Magnesium corrodes and the steel pipe with the natural gas does not corrode. Same principle for galvanized water pipe, the plating corrodes for the pipe. Eventually with no maintenance the base metal of the steel pipe will rust and permeant damage to the pipe occurs.

Like I was saying brass is the best all around material for a radiator because of it's resistance to corrosion. Here something for your next happy hour at the bar, it is only called rust when it ferrous metals - steel/cast iron.

Aluminum on the other hand is susceptible to corrosion, more of that cathode/anode stuff. To make aluminum radiator work they need to be electrically isolated from the chassis. Even with this the coolant is conductive enough to provide an electrical bond to the chassis. With the bond the aluminum radiator will corrode for the entire vehicle. That why aluminum radiators rot out so fast.

The Military uses magnesium gear box cases on their helicopters, magnesium is Illegal for use on civil aircraft, and much attention is paid to the cases. During manufacture special coatings are applied to prevent the magnesium from being exposed to the air, also regular inspections are required. On benefit of the military the mechanics HAVE TO do maintenance or they can get an all expense paid trip to Leavenworth, KS.

It too late for me to pull out my heat transfer book BUT from a heat flux rate viewpoint aluminum is the best material to use for a radiator, or as the designers call them "heat exchangers." I can try to look up but there is a term which is composed of two constants defining the material. The result is used to determine the best material and help the engineer "size" the heat exchanger.

Eagle is right aluminum radiators rot out do to galvanic corrosion, and for us mere mortals cooper is the best choice; however, if you are anal retentive on maintenance, change your coolant on a regular basis, and have a motor which is pumped up for horse power then use an aluminum radiator. You may also have to use dex cool since it has a lower pH when compared to normal green coolant. I don't want to get into a dex cool discussion right now.

For peace of mind get a good name brand cooper radiator.

Simplest fix of all and only costs a couple of bucks is a new pressure bottle cap. All the OEM thermostats and 3 core radiators in the world will not help if that stupid little rubber gasket in the pressure bottle cap is not doing it's job.

Your themostat is probably not a problem, OEM or not as long as it's a quality one.

Before you waste any time or money on this BUY A NEW CAP. I spent a ton of time and money on my '88. The cooling system is better than perfect now, but I had problems with it overheating and boiling the coolant until I replaced the pressure bottle cap.

Cap

I bought a new cap from Chrysler and the darn thing leaked worse than the old one. I took the gasket off the new one and installed it in my old cap, and viola! No more leak. I'm going to find me a rubber gasket or two of the correct size to have on hand. Better yet, this Christmas, Santa is going to bring me a new 1.5 Quart Moroso bottle with a REAL radiator cap.

Re: Cap

XJTripp said:

I bought a new cap from Chrysler and the darn thing leaked worse than the old one. I took the gasket off the new one and installed it in my old cap, and viola! No more leak. I'm going to find me a rubber gasket or two of the correct size to have on hand. Better yet, this Christmas, Santa is going to bring me a new 1.5 Quart Moroso bottle with a REAL radiator cap.

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Or just go to the local junk yard and grab a pressure bottle out of a pontiac. it is larger than the stock one and comes with a real metal cap. it will fit if you take the old shelf out and move the ac lines a little. There is a right up somewhere, i forget where... I will post a picture of it.

RINGKONG:
Questions about your picture:

Is your system converted to the "open" ('91+) type?

If so, does the tube from near the cap lead to an overflow bottle?

If not, is there another hose from the bottom of the tank or does the coolant circulate thru the top hose?

Also, where does that small tube go that taps off the brass(?) fitting in the heater hose?

Thanks.

Larry A. said:

RINGKONG:
Questions about your picture:

Is your system converted to the "open" ('91+) type?

If so, does the tube from near the cap lead to an overflow bottle?

If not, is there another hose from the bottom of the tank or does the coolant circulate thru the top hose?

Also, where does that small tube go that taps off the brass(?) fitting in the heater hose?

Thanks.

Click to expand...

No it is not converted to the open type. the tube leading from where the cap is ... is indeed a overflow tube... leading directly to the ground. the other tube from the side on the top is the recurculating one. I had to get a splice to go fromt the two different size of hose. if you look at the bottom you will see the other hose.

the brass fitting is for my water temp gauge.. the OEM one sucks.. the aftermarket one would not fit in the head.. and I couldn't find a brass fitting large enough to fit where the water temp sensor for the fan in the radiator is. so I comprimised. its pretty accurate.

the cap is a 15lb radiator cap(it came with the pressure bottle of off the pontiac). I have no idea what the jeep is rated for... but I haven't blown it yet.

martin said:

It too late for me to pull out my heat transfer book BUT from a heat flux rate viewpoint aluminum is the best material to use for a radiator, or as the designers call them "heat exchangers." I can try to look up but there is a term which is composed of two constants defining the material. The result is used to determine the best material and help the engineer "size" the heat exchanger.

Click to expand...

I must respectfully disagree that aluminum is a better conductor than copper. Right now there is a new trend in heat sincs for computer CPUs. The old standard was all aluminum, but now the trend is to use a copper insert to promote heat transfer. Copper has show in measured tests, to increase the disipation of heat from computer chips rather than using aluminum by its self. One reason they don't use all copper is the weight factor. Look at the fancy new (and pricy) computer chip coolers and you will see a copper plug in the bottom.


There was a big write up about it on www.tomshardware.com and www.overclockers.com if you do a search for the tech articles.

Tom Dennis

Anthropy said:

I must respectfully disagree that aluminum is a better conductor than copper.

Click to expand...

First off heat transfer is a black art, not a science. The problem with getting heat out of a computer processor and into the heat sink is there is never a perfect thermo conduction. This situation is called "Thermal Contact Resistance".

Also with computer heat sinks you are talking about fins and sizing those can make you head spin. The fin sizing equations use e you know the inverse of natural log to figure out critical length.

Heat is tranfered 3 ways: Conduction, convection, and radiation. So how cooling air flows through the computer case has a great impact on how hot a computer processor works. I personally think more effort can go into computer processor heat sinks. There can be more work on fin spacing and fin length.

So what does computer processor heat sinks have to do with radiator material for an XJ, no much.

As pervious discussion on here have revealed the XJs radiator is not optimal. The shoe horned in the largest radiator they could. A lot of design applications are just that, fit it into the space available.

I had a professor who told us he was testifying before Congress. They were discussing energy demand. I am sure most of us know the rule of 72. Say you get 6% on your money in the bank, the you divide 72 by 6 to find the period of time to double your money. In this case it is 12 years.

This professor told congress with a 5% annual growth in electrical energy demand that in 14.4 years the energy demand will be double - you know a simple math relationship. One of the congressmen responded "in your opinion Dr Culp".

I feel like Dr Culp, told you guys what the facts are and you doubt what I say. That your right. If you recall I bascially said to avoid aluminum raditors because of the corrosion problem, even if they do peform better.

For any of you who have a Degree in Mechanical Engineering and had a decent heat transfer professor you understand the point I am making.

There is a lot of interesting stuff in heat transfer. There is a critical radius of insulation you can place on items and actually increase the heat flow. So among the many things you have to check is to make sure when you insulate you have insulation thicker than the critical radius if you want to keep heat energy in the item.

Guys, we all can have fun just sign up at your local college and take 14 hours of calculus, 3 hours of differential equations, 6 hours of thermodynamics, 3 hours of fluid mechanics and then 3 hours of heat transfer. With all that we can warp our minds doing heat trasnfer problems as we enjoy a cool beverage of your choice!