89 XJ water reservoir keeps overflowing/ overheating

I noticed that when the weather started getting better that my engine temp would start climbing to around 230 and so i replaced my thermostat, hoping it would be a simple fix. But with my luck that only made things worse so i went and replaced my water pump and flushed the system and i even put some cooling system sealant in it, the stuff that looks like milk. And you guessed it, still didn't fix it, so nom im checking all the vacuum lines and checking the block for cracks and i find nothing, so the only thing i can think of is the reservoir cap, so i got a replacement from napa auto and i started it up. it worked fine for the 15 mile drive home and then when i shut off the engine, i could hear a bubbling and boiling noise so i opened the hood and there is water boiling out the cap spewing all over the place, it doesn't do this when its running, only when i shut it off. and when it cools down i look inside and the reservoir is completely empty. I know my radiator is old and has some fins missing in some spots so that is gonna be the next thing im gonna replace, ooh and i can only run water and not antifreeze cause im not gonna have it leak all over the ground so my pets can lick it up and die. any advice would be greatly appreciated.

Your cap leaks. You need either a new cap, or a new overflow bottle. It's not uncommon for the caps to strip.

I actually just got my new aluminum overflow bottle in the mail today, and returned my NAPA overflow bottle since it started leaking within the first month. In theory with the aluminum one with a pressure release metal cap, I should never have problems again.

~Scott

I just bought a new cap, but the reservoir is stock the cap is set to 15 lbs and fits perfectly. maybe a new reservoir or something, would that cause the overheating?

If you have any sort of leak in the system, yes. A closed system (which we have) must be CLOSED. Meaning it pressurized. My overflow bottle did the exact same thing 3 times even when the cap was tight and felt fine. Try putting a thin strip of duck tape on the overflow bottle threads, and tighten the cap up. Almost willing to bet that will solve it.

Did for me. :thumbup:

~Scott

if you get a new cap, get one from the dealer. every aftermarket cap ive tried has leaked if i didnt get it on juuuust right. dealer ones seal every time.

Muddy Beast said:

I actually just got my new aluminum overflow bottle in the mail today, and returned my NAPA overflow bottle since it started leaking within the first month. In theory with the aluminum one with a pressure release metal cap, I should never have problems again.

~Scott

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Can I ask where you got the Aluminum overflow bottle?
Thanks James L.

v8eater said:

Can I ask where you got the Aluminum overflow bottle?
Thanks James L.

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Off a guy here. But it's a Mac's radiator one or w/e. Check the interweb. They run like $130 new.

~Scott

Hate to break it to you, but you are wasting your time with the old "closed" system. You need a new radiator anyway. Don't spend big bucks for a fancy tank. I was curious, so I looked at my favorite source for that type of weird shit..........Summit....cool shit, good prices. Yeah, about $130 for a tank and then a new radiator? Anyway, put the money into a good all aluminum radiator and convert to a normal American system. Ditch the heater valve and run direct hoses. That is my opinion. Hopefully Ecomike will chime in and give you the other side of why you should keep working on your old "closed" system. You CAN go either way. IMHO, you can choose between the easy way or the hard way.

mine i drilled a vent hole in the reservior and put a bolt in it and that kept the tank from swelling up and over heatin but workin for 7 months now and im about to change to the new raditior system

Depends on what's going on with you and your rig. Me, I had to put in a new heater valve, so I did. Then I needed new hoses, so I got those. By this time when it came time for a new radiator, since I'd already bought a new bottle I figured what the heck why not. And then I found an aluminum overflow bottle so I grabbed that and I don't think my closed system is going anywhere.

After replacing ALL of my coolant components over a few months, I now wheel at under 210 all day. But my friends in their open systems run at or just above 210 all day. So to me, staying closed has been worth it. Once you figure out how to work the system and what to do if this and that fails, it becomes no biggy.

~Scott

I agree. The closed system works if all the components work. That means the system must make, and hold pressure (low pressure equals boil-over). I've found the dearler tanks/caps are expensive. Quadratec has them for cheaper...buy a couple. I end up replacing cracked overflow tanks about once every year or two...

If you're developing excessive pressure...suspect a head gasket or such...

jeepin89xj said:

mine i drilled a vent hole in the reservior and put a bolt in it and that kept the tank from swelling up and over heatin but workin for 7 months now and im about to change to the new raditior system

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This post is worthless with out pictures!

Details man, details, please explain.

On the bottle cap, if that is the only problem, a regular worm gear clamp on the outside fixes the cap problem.
I am not impressed with the aluminum radiators, or their plastic side tanks.

Best Radiator available is the 3 row (Really has 3 rows, not 2 rows that are the width of three rows), all brass/copper, all metal, CFS brand radiator at www.radiatorbarn.com, or DPG (one of our sponsors here).
Have you checked, replaced the mechanical fan clutch? Checked that the E-fan is coming on when it should? Do those first!

Take her for a drive to get good and warm. When you stop, get under the hood and look/listen around the rad for pinhole leaks. It may be spraying mist or vapor, not liquid that drips. That little pinhole could be enough to cause your symptoms, did mine.

Ecomike said:

I am not impressed with the aluminum radiators, or their plastic side tanks.

Best Radiator available is the 3 row (Really has 3 rows, not 2 rows that are the width of three rows), all brass/copper, all metal, CFS brand radiator at www.radiatorbarn.com, or DPG (one of our sponsors here).

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I agree with not wanting an aluminum radiator with the plastic side tanks (like stock). You want to pop the extra for an ALL aluminum radiator where the end tanks are oven brazed in place. No tank to core gasket. This is what BMW uses on their SUVs.

I won't disagree that the brass/copper old school style may be better as it is probably more robust, but in the same size package, an aluminum radiator "should" dissipate more heat.

Funny, most new cars are "closed system". Its way more efficient than the open system. The biggest issue with our XJ systems are 1) they are getting some age on them 2) the bottles suck at best. Look at a newer system and you will see that the bottles are internally webbed to keep the bottle from swelling/expanding. That constant cycle of swelling and contracting kills these cheap bottles. And of course if you have any kind of a leak anywhere in the system it just makes the problem even worse.

I plan on a bottle out of a late model vehicle in the future that will work better for our application.

Get a pressure bottle out of a different vehicle from the salvage yard and call it good.

Volvo, Chrysler, GM, Ford--it doesn't matter what it comes out of just as long as it fits in the space available and the hose will attach.

FlowKooler has an excellent article on overheating and troubleshooting: http://flowkoolerwaterpumps.com/cooling_faq/

winterbeater said:

I agree with not wanting an aluminum radiator with the plastic side tanks (like stock). You want to pop the extra for an ALL aluminum radiator where the end tanks are oven brazed in place. No tank to core gasket. This is what BMW uses on their SUVs.

I won't disagree that the brass/copper old school style may be better as it is probably more robust, but in the same size package, an aluminum radiator "should" dissipate more heat.

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Here is my read on that. The aluminum ones may work better at first, but I think over time they go down hill faster that copper/brass. By the end of 2 years the copper/brass starts working better than the aluminum one.

Also, from what I have read the only decent 100% aluminum one available that compares to the CFS three row Brass one, is like 3 times the price.

I have a all brass 3-row in my 90 Renix and it runs too cool/too efficient even with a bored out engine. I stay around 160-170 in the summer with the whole grill blocked except the tranny cooler. Still on and always will be on a closed system.

My take on the open versus closed is this:

With everything working properly, both systems are good.

However, as the closed system was only used for 87-90, and the open system 91-01, at some point availability of the closed system radiators may become problematic.

For that reason, and that reason alone, I will switch to the open system when I have to replace my current radiator.

My .02 cents worth.

xjtrailrider said:

I have a all brass 3-row in my 90 Renix and it runs too cool/too efficient even with a bored out engine. I stay around 160-170 in the summer with the whole grill blocked except the tranny cooler. Still on and always will be on a closed system.

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I wonder if the bored out engine cools faster, thinner walls?