XJStock

Hey Guys! New user here. Running out of options, so I thought I would turn to my fellow XJ Enthusiasts for help! So, here's the problem...

Bone Stock 89 I6 4.0 closed cooling system. 107K

Everything was working fine, No overheating, all is well. Small leak at thermostat housing gasket. Replaced Thermostat and Gasket. Started to overheat, replaced thermostat again with Motorad Failsafe Thermostat, 195F rating. Top radiator hose does not get hot. Reaches operating temp withing 5 min of idle, then PROCEEDS to red line! seems like thermostat is just NOT opening up. went through the forum up and down, Seen all the normal responses. (Change to open system, Fan clutch, burp mod, Holes drilled in thermo, etc.) Fan clutch stops as soon as engine shuts off (does not spin freely). Electric fan comes on with AC but does not seem to come on when operating temp is reached and passed. Put end up on ramps(Rear end in the sky), filled through the Temp Sender. Opened Upper Rad Hose filled through there. Got minimum burping action. NEED HELP! Not sure what else to do here guys! Any help appreciated before I go emptying my wallet on the entire system!

djb383

Go back and re-trace your steps......if I'm reading correct, u had no overheat, then u repaired a small coolant leak and now it overheats. Repairing a small coolant leak, in itself, will not cause a overheat. Gotta be something else.

Have u verified the dash gauge with a infrared gun pointed at the stat cover? Fill the cooling system thru the bottle, let the motor idle (on level ground), bottle cap off, keeping the bottle +/-1/3 full until the motor has heated up, then replace the bottle cap.

Air rises in a liquid to the high point......coolant/air exit the motor at the front of the head....the front of the head/motor is also the high point.....never have understood jacking the rear of the vehicle up in order to make the rear the high point. I've read that "burping" method before and personally think it's garbage......but since it was post on the Internet, it must be true........not.

FWIW, a "open" cooling system WILL NOT cool better than a "closed" cooling system.

Ok, went back and re-read the op.......t-stat was replaced as well. Reaching operating temp (indicated by dash gauge) in 5 min doesn't sound right either (possible wacked gauge, bad electrical).

Hey Cruiser and DFlint, chime in and help the Renix bro out.

cruiser54

I'm wondering if you got a bum stat.

Was there a bleed hole in the new stat?

FWIW, be sure to replace the standard coolant bottle cap with a Napa 703-1396.

5-90

You've probably got air trapped behind the thermostat - which will prevent it opening. There are a couple of ways to handle this:

- Jack the vehicle's rear end up. Remove the coolant temperature sensor at the driver's rear of the head (7/16" hex I think. Be careful! This thing can be seized in, and they often break if you're not careful! Use a six-point wrench, and pay attention to what you're feeling. Slowly add coolant until it comes out through the sensor hole, apply PTFE paste to the sensor, reinstall. Tighten "two flats past finger tight" (finger tight + 1/3-turn.) Check for leaks after 24 hours back in service, tighten one additional flat if necessary.

- When you install the thermostat, drill two 1/16" holes in the flange, 180* apart, about midway between the poppet and the edge. Install with one hole at 12:00 and the other at 6:00. This will make the system purge itself of air during normal operation. (This is my normal approach.)

XJStock

Yeah, Second T-stat so far. The current T-stat installed is the MotoRad Failsafe. ( No bleed hole, or install arrow.) Dash Gauge worked before I started this. I DID replace the Sender, as I used a 8 point instead of 6 point deep socked and stripped the top. Learned the hard way there. But went to Oreilys and replaced.(had them look it up). Today I may finger tighten the old one back on to check for differences as I don't own a IR Thermometer.

See now as far as the jacking the rear end goes... the highest I can get it is as high as some steel ramps will get me, which to the naked eye makes the Inline six look pretty dang level with the ground. And trust me djb383, The internet wasn't my first option! I'm Skeptical of the whole sender burp as well but so far everyone says that's usually the culprit!

Even on level ground the Tstat won't open, and being that its designed to fail in the OPEN position..... and that its the second one i have installed.... i'm very confused by what is going on. Anyone know if maybe the waterpump could be the problem? what are some symptoms of a bad waterpump besides the weephole?

XJStock

Napa 703-1396. Writing that one down. Good info


Ive listened carefully while it was hot and under pressure. cap and bottle seems to be maintaining ok and not releasing. (except for the bleeder on the top). All seems in working order.

As I said before what I touched was the Tstat and the Sender. And im pretty sure the sender is accurate as the entire system gets hot(except that upper rad hose.)

Leads me to think Tstat but i just dont see it failing twice. Ive always just popped em in and was good to go. Maybe ill try the drill thing today.

djb383

Is the front of the Renix cylinder head different from the later models? Is there not a coolant bypass passage (see pics, yellow circles) directly beside the t-stat opening in the front of the head? Wouldn't any air behind the t-stat immediately escape to the side of the t-sat thru the heater hose attached to the t-stat cover the moment the motor is started? Presuming the block/head are full of coolant, coolant does flow thru the bypass the moment the motor starts, no? Shouldn't need any bleed holes drilled in the stat.....bleed holes drilled in the stat just slow down engine warm-up. Look at a Mopar factory stat and u'll see the bleed hole is designed to "seal off" (by the bb) when the motor starts (coolant flow pushes the bb into the hole). The Mopar factory stat bleeds air when the motor is off (bb falls out of the hole when coolant flow stops thus allowing any air to continue to rise and pass to the upper rad hose, eventually being purged from the system). Again, I've never seen the logic behind raising the rear of the vehicle to "burp" the cooling system.

A properly functioning t-stat will open in either air or liquid as long as the air or liquid heats the t-stat to it's designed open temp.

XJStock

Yeah thats exactly what im working with. I noticed that notch and figured thats what its there for. But now im not sure seeing as the two thermostats are not working. I cant remember if that notch connects with the heater hose or if it goes into the upper rad hose. If its connected to the rad hose wouldnt coolant still be able to flow through? hence why i think it may be the water pump not pumping water through. oh man i dont know. Ill have to update you guys as I mess with it some more

djb383

That notch is connected with the heater hose and is part of the coolant bypass loop. The bypass loop returns coolant to the water pump where coolant is pumped thru the block, up thru the head, out the t-stat cover heater hose, thru the bypass tubing and back to the water pump over and over and over again. There's a continuous coolant flow "loop" (presuming the water pump works/no major blockage) the moment the motor is started, hot or cold, t-stat open or closed.

djb383

This water pump didn't leak.......but it didn't pump either.

PocketsEmpty

wow, what was that thing pumping, sulfuric acid??? lol

That was going to be my guess...are you sure your pump is in good order?

djb383

It was pumping years of owner neglect.

XJStock

Haha. Id say that one has seen a neglected electrical system and overheated batt once or twice. Id hate to see the rest of the engine compartment.

Not sure If its pumpin or not. But.... the heater hose does gets hot. And you're saying that the coolant located there circulates from the pump....So immediately when I start the jeep, coolant pumps into the pressure bottle from the heater hose.(I remember seeing it when looking at the post with cap off) .... so in theory that means the water pump should be pumping....right??

I'm new to this system and I guess I should of looked into this more when I realized I didn't have a rad cap to pop as i'm used to.

Your time and help has been greatly appreciated so far youz guiz.

XJStock

In my mind..... I've got it narrowed down to yet another bad tstat...
Or this strange .....infamous air bubble. . .
the latter being one i'm leery of seeing as I've never run across the problem before.

*Note- Remember- Everything was fine.... up until I decided to replace that tstat gasket and thought "well while I'm at It ill throw a new tstat."

tiwvr1

Surprised know one posted this, ARE you SURE the tstat is not in up side down? Large copper pellet and spring go in towards the head.