sturoc

92 -4.0 Sport 5spd a/c
did a search on this but did not find same threads: usually had something else going on in them.

Just did a t-stat replacement. Symptoms included No heat, temp gauge gradually rose to just below red zone before I shut down. top hoses cold.
Jeep has sits outside typically... But for 3 nights Temps have been below 0 here in CO My mix was not ideal for these conditions to say the least there was more water than antifreeze. But I had started it up various times all day to keep it warm and at night before hitting the hay. So maybe there was some ice build up in radiator.

After new t stat went in.Did a proper mix of Antifreeze more like 70% antifreeze to water filled while engine off the added a touch while running. Heat came up great, tempo gauge reading good . But as I did test drive for 40 min with 2 stops in between . the temp gauge would slowly creep up to 200 then back down to 190 at various times. Dependant on cruising, coasting ,at a light etc.

Off the top of my head sounds like a bit of air in system even though i ran it w/o cap for a few minutes for burping.
Any thoughts ?

KHester

What temp themostat did you use?

djb383

190-200 sounds perfectly normal with a 195 stat and using the heater in cold ambient temps.

EdZ

How long has this thermostat been in use??? A sticking thermostat will eventually fail... I always make a small hole (about 7 or 8mm) on the face of the new valve... Place the valve such that the hole is at 12 o-clock postion... This allows air to pass by while filling with new antifreeze thus preventing an air lock behind it...

cruiser54

That's a pretty big hole!! I've done 1/8" before.

salad

+1

If you get it cold enough you might even see lower with the fan on max.

sturoc

Duralast (autozone) 192 deg T-stat

Prior to this change my temp gauge was always pretty steady save for the usual hot days, rush our traffic and uphill crawls etc.
My Elect fan works as it should too. Might be just that, maybe it is kickin in and shutting off as it quickly cools ?
I know to take the stock temp gauge readings with a block of salt !
But my gauge has been pretty consistent and not erratic ever.
It has been wicked cold here in CO this week though so not having seen these temps in a while it may be systems reaction to it.
I mean an average 5 deg in daytime is not the norm for this time of year here.
Normally it would cruise at around 200 degrees (again a stock gauge reading )
Then again there could still be ice in system melting away

If there is air in system what is best way to purge ?

UPDATE: Checked coolant level looked low, poured some in and started up- got it to temp and see the dreaded drip-drip from under the radiator !
Jeep had been parked in heated garage past two nights maybe it finally thawed out totally overnight but had small break due to ice once melted it leaked..
Did not see this yesterday so that may have been a contributing factor or the cause making pressure fluctuate ?
Seen this decades ago when I had a 73 Challenger I took up the mountains one weekend and got really cold Ice built up in system and until it melted the temp gauge was erratic. overheated... Ugh !
Radiator under lifetime warranty so thats a good thing and Guess I will do the water pump since I'll have the room to work after pulling radiator out.
217K on the stock water pump !

But please offer replies, tips, & info related to first part of post.
Thanks as always !

EdZ

If your using a 50/50 mix with the antifreeze, then it is not likely to freeze solid... Even if you get it cold enough to freeze at all it usually turns into a slushy mix... I drove a car years ago in -40 degree temps... The thermostat never did open (never got engine to come up to temp) and the radiator ended up freezing (turned into slush)... If I let it just sit and run for 20 minutes or so it would just start to come up on the temp gauge... As soon as I started moving again it would drop back down to the cold position...
The fluctuations you are seeing is likely due to the cheap T-stat (Duralat)
you put in... I would spring for an OEM stat as they seem to outlast aftermarket several times over... If it is the stat sticking, then it likely will continue to degrade till it just won't open at all...

sturoc

whats its worth i did not go for the cheapest t-stat on their list.
We've had 15 below and 0 daytime for 4 days now. Jeep is parked outside and was only warmed up for a half hour a couple of times a day
Didn't drive it much no need to go out lately. As stated my mix was not the best and old.

Weather is starting to warm up to now finally... its 5 degrees out !

EdZ

5 degrees, heck it's just about T-shirt weather then...

There are three areas I choose not to skimp on, cooling system, lubrication system, and the brake system... All of these areas cost far more $ over all when neglected or skimped on...

sturoc

EdZ ....Indeed !

sturoc

Another update :

After replacing radiator, water pump, fan clutch -good thing on that one it was grinding upon turning by hand ! And a general once over on the front end area. Got all together and ran up to operating temp and the stock water temp gauge still doing the same fluctuation.
Temp goes up to 205-210 then as I speed up drops 10 -15 degs and cruising will slowly climb again to that hi point temp.

I have not replaced the 'new' t-stat yet, wanted to get the above major stuff done.
So today I will get another brand from another parts store.
Water outlet (gooseneck) is brand new- replaced when i first did the T-stat last week.
Should be good to re-use that ?

Sure do hope that solves it cause i don't know what else it could be at this point.

cruiser54

Get a stat from the dealer and return the POS ones to the parts store.

EdZ

Is there any air bubbles seen in the radiator while idling ??? How about when ya rev the engine a bit after letting it idle for a bit (get up to 210) ??? Exhaust gases excaping into the antifreeze can raise the temp... Sooner or later it will start leaking back into the cylinder (white smoke will be the indicator)... If this process has started already, sometimes you can identify the cylinder with the leak by looking at the spark plugs... It will be the one that is really clean (steam cleaned) with no carbon on it...

But the t-stat would be my first choice (if no air bubles are noticed in the rad)...

sturoc

Did the uphill purge trick :
Started XJ w/ cap off and parked nose up on uphill
Got up to temp and a bunch of bubbles came out then slowly dwindled to a couple here and there But I only ran it for maybe 5-8 minutes.
topped it off a bit buttoned 'er up and took for a test drive.
Outside daytime temps here are at 40 degs. now

Gauge still had movement not as drastic though.
If I had to guess temps I'd say 205 ish to 190 but on that gauge getting an accurate read is a feat.
Goes up and down at steady speed and calms at idle and moves on acceleration etc.
BUT never gets hot i.e never over 210, though heater is great / normal.
No exhaust smoke
Oil is good color as is the Antifreeze
Engine runs smooth like it always has, especially for over 200k !

Changing T- stat today will update after.