*EDIT: Please forgive my silly typo in the title.

Hey all,

Forgive me I know there are many threads on this but I'd like a second opinion. I opened up my radiator cap today and found this:



The sludge is kind of foamy but pretty baked on underneath the surface foamy layer. So more info...
Jeep has been running fine .
Never overheated while I've owned it
0 exhaust smoke0 evidence of coolant in oil
Engine was completely flushed with water and chemical flush about 6 months ago, refilled with 50/50.
Nothing is leaking
I have replaced two fail safe thermostats in the last couple months, both due to becoming stuck in the open position. In the middle of winter. Not sure why, never overheated as I mentioned, so I switched back to a normal style thermostat. Not sure if that is related.
Jeep runs just below 210 at all times.
I noticed that I'm slightly low on oil. I remember oil was over-full when I changed it a few thousand miles ago.
Coolant Resovoir was completely empty. I've since added.

To my knowledge a blown gasget would cause coolant in my oil. Could this just be a really bad case of rusty coolant?

I don't have a coolant tester but I put a rubber glove over the rad to see if there were any gasses coming out. It seemed to be the opposite, the glove was sucked in slightly when I revved the engine, no gasses. I have not done a compression test but I can rent from AutoZone if need be.

Ideas?

 

I am curious what your tranny fluid looks like?
If it is an automatic.
Couple guys recently have posted, maybe one here and second on another XJ forum, about the tranny cooler in their radiator busting.
Until then never even heard of such a thing but.......

 

Just checked. Tranny fluid is clean

 

It was kind of a stupid idea but.... LOL.

 

The fact that your coolant reservoir was empty (have you searched for leaks??) and the look of that coolant would prompt me to run a compression test for starters. Easy to do on the 4.0 and a good snapshot in time of the internal condition of the engine. You could also perform a "block test" (sold at many parts stores for around $30) that sniffs the coolant for the presence of hydrocarbons.

But if this were mine, I'd start with some compression readings as testing and data are always your friend. Also, when you flushed and filled your cooling system last time, was that done with tap water or distilled water?

The compression spec for the 4.0 is 120-150 psi with no more than a 30 psi variation between cylinders.

Good luck and keep us updated!

 

Update on this:

So I gave her a thorough flush yesterday. She was pretty blocked up, especially in the heater core. Aside from under the rad cap and in the heater core however, it was all just brown water, not too much more mud. But there was plenty under the cap and in the heater core as mentioned. The small reservoir hose was also completely blocked with sludge. Its likely she wasnt getting any extra coolant for a while, not sure if that has an effect. The sludge and water did not make any sort of oil slick on the ground and sprayed away easily with the hose, which i'm hoping means it's not oil. I flushed her out with the hose until she ran clean, right now shes full of hose water and flush chemical. I'm going to let that circulate until tomorrow, flush again and refill with 50/50.

I will say that it didn't really seem like the rad was circulating right. I'm not really sure how its all supposed to look. The system wasnt building any pressure idling. It is the winter and it was cool out. Engine stayed perfectly cool the entire time and I let her idle for a couple hours. I also drove to work this morning about an hour. I had a hard time yesterday getting the upper rad hose to pressurize as well. It felt like it was full of air and no amount of squeezing, revving engine or forcing in water seemed to help. The pump is definitely working fine, when I took off the upper rad hose with the engine on plenty of water (brown again after flush chemical added) was coming out. I'm not really sure in what amount it is supposed to come out/with how much force it should come out however. So who knows.

I plan on compression testing asap.

I also changed my oil which was completely clean.

When I google "rust in coolant", the images all look exactly like mine. I also searched "oil in coolant" and they looked much different so I think thats a good sign. But why would there be so much rust if thats the case?

 

The "hose water" you're using, does it come from a well? Are you using premixed coolant or diluting it with hose water?

My well water is like liquid limestone, so I either buy premix or use distilled water. Your system looks like just pure hard water with lots of iron in it.

 

I live in NYC so the water is pretty good. And I used pre-mixed 50/50 last time and will this time as well. So are everything I've done is exactly what I did last time so I'm worried this will happen again.

 

Have you tried a magnet to see if it's iron or just mud? If it's iron, something is eating the inside of your engine. IDK what unless your system Ph is way off. The Ph should be held at around 10 (8.5 - 11). Below that it will attack steel and iron. Above that it attacks aluminum. You can get a test kit at NAPA. It can be adjusted with chemicals, but which ones, I'm not clear on. 50/50 premix is about 8.75

 

This is a good idea I didn't think of that. I'll try it out and see.

 

After the chemical flush, go to the store and pick up a few gallons of distilled water and just run plain distilled water through it, maybe even 2 or three times. The water from the hose is probably not too bad, but not as good as distilled. Distilled water is only like 1.00 a gallon anyway. For 10 bucks you can flush the system 3 times, and make sure it is real clean.

 

You would think pure distilled water would be a neutral Ph 7, but it's not. The longer it's exposed to the air, the more carbon dioxide it absorbs. It can be as low as 5.8 which is quite acidic! Your water in NYC comes from reservoirs here in the Catskills and contains quite a bit of limestone which makes it more base than distilled water. Remember each full number on the Ph scale represents a 10-fold increase or decease in acidity or base number. This is why Ph must be held in the range that's advantageous to the metals that surround it. SO, coolant with a Ph of 10 is 1000 times more base than pure recently distilled water.

 

Ok results from the compression test:

1: 65psi
2:60psi
3:55psi
4:50psi
5:60psi
6:90psi

This doesn't seem good. I should add that the engine seems to be running just fine? Or maybe I've just always had bad compression....
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Are you sure the compression tester is good and the test was done properly?

 

I should mention I didn't do the "wet" part of the test. As far as the tester, it's rented from AutoZone. Unfortunately the way they designed it there was no way for me to get the tester more than hand tight by spinning the hose it's attached to. But I've used these in the past and it never seemed to be an issue.