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[Brynjaminjones]

My XJ has been like this a while now and I finally thought I should look further into it.

Last year I replaced the following:

• Radiator
• Heater core
• Radiator cap
• Thermostat
• Viscous fan clutch
• Radiator hoses
• Water pump

Since then the cooling system has been acting a little differently to previously.

The expansion tank is full to the maximum mark and never seems to vary at all.
Every time I look under the radiator cap the level has dropped slightly (every few weeks or so) and takes a bit more coolant to top it off.

If I squeeze the top radiator hose, it normally burps some air out of the radiator cap. I squeeze it until it stops doing this and top off the coolant. A couple of weeks later when I try again there seems to be air in that hose again.

The temperature runs 1-2 bars under the middle mark and only very occasionally makes it to 100, so there's no sign of overheating at all.


Jeep runs otherwise fine - idle is fine, oil looks clean, radiator cap is clean, nothing unusual out of the exhaust once warmed up, performance is fine and gets 24mpg on a run.

What exactly does this mean, and where should I look? 

[bgbazz]

My guess is that you have a bubble of trapped air in the system (a likely culprit is the heater core)...maybe pick a cool day, turn the heater control up to the max setting, wind all the windows down and go for a long drive...that should ensure that the system gets a complete flow throughout.

Otherwise, just keep doing what you've been doing and it will eventually purge itself of air.

[daggie]

core plugs weeping

[Brynjaminjones]

Thank you for the replies. I was thinking along the lines of there being air trapped somewhere, but I thought these things were self bleeding after a few warm up cycles.

Aside from running a little hot, the cooling system operated completely normally before replacing everything (the old leaking heater core was bypassed at that point but I don't think that makes a difference).

Can you explain how a weeping core plug would stop coolant being taken from the expansion tank?

Sent from my HTC One M8s using Tapatalk

[daggie]

"Every time I look under the radiator cap the level has dropped slightly (every few weeks or so) and takes a bit more coolant to top it off."
core plugs leaking on the 4.0l is common
a weeping core. plug will let water out, air will also get in,
there's six plugs down the left hand side of the block, you should be able to see them from various angles with a mirror,
the one you can't see is the one in the bell housing, usually an oily/watery drip

[LairdScooby]

I had something similar on my XJ and it wasn't core plugs but an air lock caused by the heater matrix being connected back to front! The feed hose from the 'stat housing should go to the top stub on the matrix to minimise air locks, ensure best flow through the matrix and best output from the heater.

This was just one of the faults i found in my cooling system as the result of a poorly installed LPG system that i've worked through and eventually got everything working as it should.

You could also try parking facing downhill slightly and loosening the temperature sender on the rear end of the cylinder head to let any air locks and bubbles out of there - it's a slightly higher point when level than the 'stat housing so air locks seem to gather there which seems to cause the gauge to go up and down a bit.
Alternatively park facing up a steepish hill and warm it up then let it cool down - this should hopefully get any air locks/bubbles to the thermostat and out through the top hose. This will find its way out of the expansion tank pipe and tank.

[Brynjaminjones]

I'm still puzzled by this.
As far as I can tell there don't seem to be leaks anywhere, but I keep finding air in the top radiator hose that I burp out by squeezing it with the radiator cap off.


I was stuck in traffic yesterday for an hour and a half, which is the only time the engine ever gets right up to temperature. It got hot enough to get the aux fan on and off several times, but once moving again it cooled back down to a bar below 100 almost instantly, so it looks like everything is working okay.


The heater output is also good.


Daft question, but what's the best way to spot a small coolant leak? Do they usually leave deposits?

[LairdScooby]

Daft question, but what's the best way to spot a small coolant leak? Do they usually leave deposits?

It's not a daft question at all and the answer is "usually". However, i had a leak on my last Volvo 740 that caused a misfire when hot. Similar symptoms to yours on the coolant front but add in a misfire for extra headache value!
The relative positions of the top hose and plugs are the same on the Volvo as the 4.0 Jeep so this is more relevant that you first thought. here was a pin-hole in the top hose that was spraying water out when the engine got hot enough. Trouble was it was such a fine jet of water i couldn't see it, only feel it but it came out at a fair pressure so reached a long way - including the dizzy cap at the back of the head between the head and bulkhead and all over the plug leads and plugs. One set of rotor arm, dizzy cap, plugs and leads later i thought i'd fixed the misfire but not the coolant loss, which because it was only a pin hole was only slight but i wanted to get to the bottom of it. However, it was still misfiring which puzzled me so i took it out one dark night to try and see if it was arcing out anywhere.
Reaching in from the drivers side to grab the throttle and rev the engine, as i passed my hand over the area of the plugs to reach the throttle on the passenger side, my paw was shot with wet stuff.
I tried again and got wet again and left it there longer - long enough to realise it was hot (very F-Hot!) and i then managed by feel to trace it back to the top hose. Squeezing the hose out of shape i saw the pin hole which of course closed when the hose wasn't under pressure so no residue was left on the hose as it was washed away every time it leaked.

Usually there is a crystalline greyish white deposit from a constant leak (calcium/limescale in the water), sometimes this is tinged with the colour of the antifreeze. One leak i found on my Jeep that showed up this way was where the top hose joins the 'stat housing. The housing was generally corroded as well and the 'stat wasn't sealing properly inside so i renewed that and cured the leak anyway. I also followed this advice to try and get a more stable temperature :

http://www.go.jeep-xj.info/HowtoRadiatorRestrictor.htm

It's worked for me although i still get a little variation it's much more stable. I suppose if you still have a coolant leak that you can't find, you could try something like Radweld, K-Seal, Barrs Leaks or similar but please take advice from a few others on here to make sure there aren't any small bore coolant channels that can become blocked on the Jeep using this kind of thing.

[Brynjaminjones]

Thank you for that. Funnily enough, my Jeep does misfire if you shut it off when very hot then start again before it's cooled down, but I think that's down to heat not exiting under the bonnet once the fan turns off.


I've just been out and started the Jeep from cold with the radiator cap off, and there was the odd bubble here and there for a couple of minutes but then it stopped really doing anything of interest.
Interestingly, the coolant didn't really require topping up, and it's got to be at least a couple of weeks since I last looked at it.

[LairdScooby]

Maybe your leak has fixed itself - the greyish white deposit/limescale sometimes creates its own seal and fixes minor leaks. Either that or as mentioned above, you had an air lock and it's finally gone.

[Brynjaminjones]

I never got around to finally updating this...

Finally I decided to give in and look at the core plugs (I'd avoided this for fear of the worst) and sure enough, the front one on the side of the block has a definite weep. This is beyond the realm of what I think I could get away with at home with the tools I've got, so for the first time since I've had her, I've booked my XJ in to be sorted by somebody else!

I do however still have one question:- Why is this leak preventing coolant from being sucked in from the expansion tank? I appreciate that air is being sucked in, but the ZJ has had several different coolant leaks (mostly LPG kit related) and it always just takes coolant from the expansion tank like normal. The coolant in the expansion tank on the XJ on the other hand hasn't moved at all in over a year now!
Could I have another malfunctioning component somewhere?
I was wondering if this could be caused by a bad/incorrectly rated radiator cap?

[LairdScooby]

The rad cap might be faulty/incorrect pressure forcing too much pressure into the system or possibly not enough pressure in the system. Either would probably prevent the normal expansion/contraction of the coolant and the "suck back" of coolant from the tank.
Also the core plug leak would probably mean air is being drawn into the system and causing air locks which would further prevent the coolant level altering as it normally should.

I've renewed core plugs in the past by spearing them with a pry-driver (an old screwdriver - a friend calls screwdrivers you don't mind using as levers, chisels etc "pry-drivers" which i think is a very apt description) and levering them out. Then clean the aperture with some emery or wet and dry paper, dry it, apply some sealant to the new core plug and use a large socket as a drift to knock it in.

[Dave69]

expansion tanks are just that...they accomodate the water expansion due to temperture, they dont provide a constant top up and collection every time the jeep is run so dont get too confused by the level of fluid in the bottle. As log as its between the upper and lower level its ok. A year without moving is not something to get worried about.

Leaking coreplug, you can patch the edge with a metal filler for a cheap temporary fix.

[Brynjaminjones]

Cheers for that.

Scooby, I understand that the core plug could cause air locks, but my previous experience with both Jeeps is that they quite happily self-bleed and replenish from the overflow when there's a leak. The only changed component I can think that would affect this is the cap. I've now been reading all about vented and un-vented caps in various pressures and have become fairly confused about which my XJ is supposed to have!

I'm quite happy about the actual removal of the core plugs, it's the exhaust manifold and other bits that I really don't want to have to take off this Jeep for the third time!

Dave, I don't mind that the level is correct, but by looking at the coolant in the bottle it clearly hasn't ever been topped up or depleted as it still looks brand new, unlike the stuff in the radiator. It always used to simply suck from the expansion tank before I replaced everything. I just find it a pain having to wait for it to cool down then top up at the radiator all the time, especially as this sin't how it used to behave.

It's having the plugs done on Monday by PeakJeep in Chesterfield - I've been quoted £235 to have all the ones down the side of the block done

[LairdScooby]

Might pay to get them to renew the expansion and rad caps when they have done the core plugs and then pressure test the whole system. I would think after doing the core plugs they would pressure test just to check but maybe not.

Logic suggests the rad cap should be unvented and the expansion cap should be but sometimes things don't always work as you'd think. Maybe someone can shed some more light on this?

[Brynjaminjones]

I've done a bit of research now, and managed to find from multiple sources that the cap should be a 16psi vented one. I did next to no research when I bought the previous one, so I've ordered a new one as for £9 there's no harm trying, even if I just end up with a spare.

Sent from my HTC One M8s using Tapatalk

[Dave69]

as they say you learn by experience, and remember there are two types of cooling system, a closed and an open. if i remember an open refers to to a system without a header tank and a closed systemr eferes to the modern setup with the plastic pressurised tank where you fill rather than at the radiator.