EddieForager

I just did a compression test - what do you think of these results ?

135
165
165
160
155
170

A wet test was done on the 135 and it stayed there - not sure what that indicates. big gap from 135-170. That 135 sure stands out.

96 XJ i6 4L - overheating at idle and while driving all speeds. New water pump, flush, rad cap.

Now I'm really confused... looks out of place but if I had a bad HG wouldn't it be much lower ? Since it failed that engine block test (chemical hydrocarbon thing) I fully expected at least one bad cylinder. Aahhh

DFlintstone

I'd wager a small crack on #1 exhaust valve. I guess if that's the case it will get worse pretty soon.

They CAN put a smog "sniffer" to the radiator to check for hydrocarbons in the cooling system, (from a bad head gasket)

I assume you got the tester on there good behind the compressor there. "back in the day" my Dad talked of being within 25%. So you clear that mark, but 15% is more like it.

If it idles OK I guess you don't have an issue like push-rod off....Guys have posted having their rocker pivots totally shot. I guess if you DO tear into it you might watch for something like that.

EddieForager

That sniffer is I think pretty much does what the 'engine block' test was. That test indicated I had hydrocarbons in the cooling system. But I'm not sure I trust it - others have said it can produce false positives.

It was a PITA getting the tester on for the 135 so I tested twice with the same result..it was good and tight.

It does idle just fine - maybe a slight lifter tick I think. Speeds up when I increase throttle.

There seem to be no other signs of bad HG other than overheat. No mixing of fluids, power seems good, spark plugs are clean, no smokey exhaust.

Willys55

my money is on a burned valve, since the wet test failed to produce a change.

you didn't mention if it smoked at idle so I ruled out rings...however I have had two of those engines in that last three years that had score lines in number one cylinder and produced similar compression results

EddieForager

No smoke at all... other than overheating there are no other symptoms I can see. I did see bubbles coming up in the reserve tank on 2 occasions though - that can't be a good thing. Could that just be trapped air escaping ?

DFlintstone

Whoa...either I missed it or you edited. Failed HC test and overheating? Head gasket. Just a little 2000* combustion gas leaking into the water jacket will heat up the coolant, for sure.With those readings you can't go too far wrong pulling the head, having it checked and running it. You could go through your cooling system now, but you might be chasing your tail.

The weekends can be slow here....you might bump your post during the week and maybe get input from some of the others.

******, the oil on the wet test only helps seal the rings. The gasket/head and valves are left.

I don't fully get "leak-down". That said when I put compressed air to the plug hole in my old Onan Generator I could tell the exhaust valve was leaking from the sound of the hiss out the exhaust.

Eddie, if you top up the radiator, to the brim, then "power-brake" it, (cap off), do you get steady bubbles?

EddieForager

I've never tried that but can give it a shot tomorrow. Will post back here with the result.

Thanks everyone for the help.. great forum here.

DFlintstone

You are very welcome. I hate when that stuff happens. Let's hope its just the gasket.

If course be very careful power braking it. It takes two, and no-one stands in front! I had one slam a geyser up at the hood once. That test won't tell you its good, but sometimes it's pretty clear if it's bad!

There will be some surging that makes it tougher....

BatmanXJ

X2 on Burnt valve

BatmanXJ

I did not do a compression test on mine. I had very similar symptoms as you. This is what I found when broke down. Cylinders were really good considering 290K

EddieForager

I'm feeling silly now. Today was the first cooler day since I bought the jeep - it was overheating only in town. Cooled down to just above where I think it should be on the highway. So I realized I never gave thought to fan clutch. Doh. Pulled over, popped the hood and could easily stop the fan with a couple bits of rolled up paper (note I eased into it, and stopped it only after I noticed it slowing when pushing paper against the fan). So I thought... thars yer problem right thar.


I'm gonna replace the fan clutch and see if that fixes it. If so...

BatmanXJ

I hope that is your issue. That would be great.

DFlintstone

Ok....Cool! Let us know....

EddieForager

Today I swapped out the fan clutch. Damn it was tight getting in and out between the rad... but easy job. I got a good look at the rad... behind the old clutch fan the fins are pretty messed up. Also, brushed up against some fins near the bottom of the rad and they just peeled way.

So I guess I need a rad next. Which one to get??

After I swapped the fan clutch I let her idle for 20 mins... stayed at 100C (halfway on the gauge) Then went for a drive - about 1.5 hrs. On the highway and logging roads (slow and hilly). The temp maxed out at just between 1/2 and 3/4 on gauge most of the time staying just over 1/2 (100C)

I forgot to do the power brake test.

Although it was a cool day, I have not been able to run the jeep that long without rolling down the windows and turning up the heat.

Would air temp affect the engine temp this much if it were a blown HG ?

Gonna replace the rad regardless.

DFlintstone

Guess it depends how bad it is. 130 is not "low compression".

What sort of threw me before.....at speed the fans don't matter so much. You have air. If it were to overheat in traffic or hill climbing, I'd think fan(s), (& shroud).

No help here picking a Rad. DJB or someone might chime in. Is your E-fan coming on? It comes on at 218* Now I forgot your year. Anyway it might come on also with ether the defrost or AC on. Yea, 96, I think , it should come on like that^.