Jeep 4.0L: trying AutoRX

[Zaedock]

Greetings everyone.
Last year, the coolant overflow cap on the expansion bottle on my '89 Jeep Cherokee blew off on the highway without warning (cheap plastic cap threads). Well, the coolant leaked down the fender/firewall and gave no warning until the head gasket went. I have changed the head gasket, but still have low compression in cylinders 3 & 4. Actually, at first, I had no compression in both cylinders until I let it run for 15-20 minutes and then the compression went up to 60 PSI. This is a 4.0L with 90K miles.

A couple months ago, for about a week, the compression magically went back up to 100-110psi in both cylinders! I thought it was fixed and that the rings were just gunked from coolant entering those cylinders (the truck sat with coolant in both for a couple of weeks). Unfortunately, after that week, it went back to 60-65 just as quickly as it went up. It does currently have a slight skip, as cylinder 3 & 4 are opposite in the firing order, but it doesn't run too bad. However, every once in a while, the idle will smooth out (with compression readings jumping up to 75-80PSI) and then after a few minutes it will go back to 60-65 PSI in those two cylinders. It burns none/very little oil and there has been absolutely no smoke on cold start (even on the coldest of days) running 5W30 Valvoline dino.

I currently have a low milage replacement motor to toss in, but I am really interested in trying out the AutoRX to see if it can clear up the ring packs in this engine. If it doesn't work, then nothing is lost as I have the other engine. I placed my AutoRX order today and hope to receive 'em in a few days (I'm going to try it in my '92 2.5L Wrangler trail rig too) and then I will do a baseline compression test and then change the oil with AutoRX and cheap dino 10W30 (probably SuperTech). I'm a snake oil skeptic, but I've been on here for a few years and know that many have had good results from AutoRX. The condition of my XJ's 4.0L is probably on the more severe side for any additive to try and fix, but hopefully, I'll be able to be one of the "testimonials" on their website.

Anyone here have any compression test results from using AutoRX? I feel pretty optimistic that AutoRX will be able to spruce these rings up.

I look forward to sharing my results.
Talk soon.

 

[Quest]

Since plastic coolant overflow tank cap is design to be vented, the very sign of yours blown away is a sure sign that something definitely gone wrong there, and most likely due to some sort of extreme overheating or blown head gasket of some sort.

Because your consequence is blown overflow tank cap (the cause may have something to do with headgasket failure), it would be difficult, if not too late to determine whether it's something to do with ring packs, unless the engine is completely torn apart (including the bottom end, all pistons are off the cylinders for close inspection).

In this case, I wouldn't even bother wasting my precious AutoRx ino a damaged engine if I were you, but instead: use it in the replacemnt motor to get the most benefits out of it.

 

[Rabbler]

These older JEEP Cherokee's were designed so that the expansion tank is pressurised along with he cooling system. It's not a conventional overflow tank.
The cap blowing off was not uncommon and there even was a recall for the cap around that year.

 

[Chris142]

Originally Posted By: Quest
Since plastic coolant overflow tank cap is design to be vented, the very sign of yours blown away is a sure sign that something definitely gone wrong there, and most likely due to some sort of extreme overheating or blown head gasket of some sort.

Because your consequence is blown overflow tank cap (the cause may have something to do with headgasket failure), it would be difficult, if not too late to determine whether it's something to do with ring packs, unless the engine is completely torn apart (including the bottom end, all pistons are off the cylinders for close inspection).

In this case, I wouldn't even bother wasting my precious AutoRx ino a damaged engine if I were you, but instead: use it in the replacemnt motor to get the most benefits out of it.

Those plastic bottles get soft and then the plastic cap goes flying off. Most XJ's around have been retrofitted with the newer radiator with the cap on the rad instead of the bottle.

You can also buy a metal replacement bottle to get rid of the plastic POS.

I agree that his engine is most likely damaged and putting in the replacement makes sense.

If it was my Jeep I'd swap in the newer radiator and get rid of the stupid bottle setup.......Those are nothing but trouble.

 

[Brett Miller]

Most likely the engine got hot enough that the rings lost tension. Auto-rx is worth a shot but don't get your hopes up.

 

[Gary Allan]

I say that you've got nothing to lose in the trying. $30 bucks you'll blow on ancillary parts in the swap of the new engine. dnewton3 didn't think A-Rx would work either. His ring coking was due to an overheat too.

You may get lucky.

 

[Zaedock]

I had bought the XJ from the original owners (older folks). I plan to upgrade the radiator to the 93-94+ version with a real radiator cap when I install the new motor.

Currently, I have a hose clamp around the replacement cap to help keep it there as a precaution. The engine might be worth saving because the compression returns once in a while. It also hasn't used any coolant since I've put it back together and there is no bearing noise. I'm in the process of adding new gaskets to the replacement boneyard motor. It currently runs and it's not my only vehicle, so I'm not in a hurry. That's why I thought this would be a really good test of AutoRX. That in itself is worth the $30 to me.

Who knows, maybe I'll get lucky.

 

[TooManyWheels]

Even at your highest, 110 lbs is about two-thirds of what it should be. But, as you say, it is a cheap experiment.

 

[brian]

You might have another problem.

These Jeeps sometimes have problems with the exhaust valves, exhaust valve guides, and exhaust valve seats. Mine had an intermittent rough idle and a compression test showed #1 and #6 at 50 and 85 pounds respectively. When the head was pulled all exhaust valve seats were messed up.

Did you have the head checked thoroughly when you changed the head gasket?

-brian