Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Brynjaminjones]

Good Morning Birties.

I'm having a bit of trouble with the cooling system and LPG in the ZJ that you guys might be able to help with.

Lately, the LPG system has been cutting out (the switch flashes and beeps repeatedly, engine stumbles then switches to petrol) if I do certain things. For example, it will often do this if I quickly go to over 2/3 throttle from a stand still, or if I accelerate reasonably hard in a high gear. It has always switched over to petrol if I'm at full throttle over about 3500rpm, but that's normal behaviour and it does that smoothly with no warning beeps. The cutting out/stumbling/beeping issue only happens below that switch over threshold.

This all coincides with several cooling system issues. I had to replace the leaking coolant pipes that go to the vaporiser, the vaporiser itself was dripping coolant (now replaced) and the water pump bearing failed, which meant a new pump and thermostat.

I'm guessing that I've still got some air in the system somewhere, but I've bled it a couple of times now and I can't seem to stop this from happening. It doesn't appear to be losing any coolant now.
The Jeep also doesn't want to run above about 75 degrees on the gauge, although both Jeeps are like that at the moment.
One of my problems is that as the Jeep is running so cool, when I bleed the system it never seems to get to the point where it surges out of the radiator cap.

Can anybody shed any light on whether I'm along the right lines or not, and how I should go about getting it working right?

[oneof24orless]

Have you checked else where for coolant leaks? T/stat housing for example. Is the stat good?



Sent from my iPhone using Tapatalk

[Hillbilly]

They may be separate issues. The LPG cutting out has given me a problem on two different 4 litres. Both occasions have been arcing from the ht leads to the block. Only happened when I gave it some welly. Any HT problems can cause a problem with LPG under load while it may run fine on petrol.

You seem to have addressed most overheating problems, but what about the fan. I can't remember whether the ZJ has the same viscous fan system as the WJ, but my WJ overheating problems were caused by a failed relay tucked inside the inner wing.

[Brynjaminjones]

Cheers for the ideas. I do in fact have a bad HT lead that used to cause it to miss under load at low RPM, but I've recently sorted that (for now) as it was acting up again (bad connector). Even so, when that plays up it never causes the LPG to switch over to petrol, it just misfires under load.


The fan is actually good - in fact, after driving it yesterday, I've realised that the ZJ is definitely over cooling. I'm now wondering if I have a bad thermostat, as it didn't get over half way to normal operating temperature after over an hour of driving, including quite a bit of idling. The heater got warm, but this time last year it used to get scaldingly hot.
This might also tie in with the trouble I'm having when bleeding, in that it's never reaching that point where the coolant suddenly surges out of the radiator neck as the thermostat opens.


There doesn't seem to be any coolant loss, so I'm fairly confident there aren't any leaks.


Does it sound to you lot like the thermostat might be to blame? It was a Crown one that I put in.

[Brynjaminjones]

Fingers crossed this should be sorted now!
Whilst at Peak Jeep I got them to quickly check the thermostat. They've found that it was stuck open as I suspected, and that after replacement it's running up to temperature, hopefully meaning easier bleeding!

[Brynjaminjones]

I think I need some more help with this. After a new thermostat I successfully managed to get some bubbles out of the cooling system by bleeding with the nose right in the air.

All LPG components are good, and the cooling system now keeps the temperature exactly where it should be, no matter how I drive.

However, after a few weeks I can now often hear the gurgling sound of air in the heater core as I accelerate once again. The coolant level has also dropped about an inch.

I don't understand why I keep getting air trapped in the heater core - does anyone have any idea what might cause this?

Sent from my HTC One M8s using Tapatalk

[The Smiths]

If it was a diesel then air in heater matrix / heater not getting hot is an early sign of head going as that's where bubbles gather first

no idea on petrol

[ommony]

How are your heater hoses routed? When I got my XJ the hater matrix and LPG condenser were plumbed in parallel (ie, the hot water for LPG system was just T'd off the heater matrix hoses near where they pass through the bulkhead). The problem I had was that the water would just take the path of least resistance and LPG would cut in and out intermittently OR the heater would be ice cold, depending on where the water decided to go. After a chat with my LPG guy, I changed it to run in serial. Now the hot water comes out of the engine, goes through the LPG condenser, then through the heater matrix and back to the engine. So the water MUST go through the LPG system first, and only then through the heater matrix. This has made the LPG kit work perfectly, and heater is also better/more consistent. Obviously no good if your heater matrix is clogged, but if all else is well, this solution might work for you too.

[Brynjaminjones]

I'm still having trouble with this.

James at Peak Jeep took a look at it, and could find nothing wrong with it other than a bad radiator cap.
I've put on a replacement cap, which according to every online source is the correct original cap.

I have however noticed that this new cap is unvented (the valve on the bottom springs closed), rather than vented (valve on the bottom hung hung open with gravity until pressure increases) like the previous cap. I don't know if this could cause trouble, but I feel like I'm opening a can of worms as it looks like the 4.0 changed between vented and unvented as well as different pressure ratings throughout the years.

I re-bled the system with the new radiator cap and got a load of air out, but it's still having the exact same trouble. It doesn't really appear to be using/losing any coolant, but I can hear air in the heater core and the LPG cuts out when you demand a lot of gas.

I'm thinking about re-plumbing the LPG system to run in series rather than parallel as ommony says below, but I don't know if this would just be masking the issue, as I had no issued with my current setup originally.

[Hillbilly]

If you reach a dead end on this, there is a garage up the road from James in Barrow Hill. Dave, the owner is very knowledgeable on LPG.

[ommony]

I have however noticed that this new cap is unvented (the valve on the bottom springs closed), rather than vented (valve on the bottom hung hung open with gravity until pressure increases) like the previous cap. I don't know if this could cause trouble, but I feel like I'm opening a can of worms as it looks like the 4.0 changed between vented and unvented as well as different pressure ratings throughout the years.

I'm thinking about re-plumbing the LPG system to run in series rather than parallel as ommony says below, but I don't know if this would just be masking the issue, as I had no issued with my current setup originally.

I'm pretty sure yours is the closed type system. The earlier ones had the open system. But I don't think that would cause your trapped air problems anyways.

If you're not actually losing coolant, then you've got to be pulling air in somewhere, or just not getting the system bled properly. This is another issue with running the water hoses to the LPG condenser in parallel - water can just take that route instead of going through the heater matrix and forcing air bubbles out/etc. If you have a partially blocked heater matrix, the water will likely only reach it at higher rpms (which seems like what you describe and could cause the bubbling/gurgling sounds).

Re-routing things in serial just eliminates that potential problem, and ensures you have water always flowing through the heater matrix. If you do try that route, just make sure you have good flow through the heater matrix (mine was totally blocked and so when I first hooked it up, lpg didn't work at all as water wasn't moving -- once I flushed the heater matrix all was well.

The other thing I always do when I've done cooling system work on my Jeep is to take the heater hoses off at the engine (thermostat housing and water pump) then raise those hoses up as high as I can, put a funnel on the return hose, and pre-fill the heater matrix (and LPG system) with coolant, then clamp off the hoses at the ends before refitting them to the engine and then removing the clamps. I seem to get most, if not all, of the air out this way.

(Also note, mine ran fine until, I presume, the heater matrix finally clogged up completely and that's when I started having problems. I can only assume that it was running for years with very minimal flow through the heater matrix and it just silted up. I was just trying to fix my heater when I figured all this stuff out. Doesn't mean it will solve your problem, but simplifying the system does make trouble-shooting much easier)

[Brynjaminjones]

Cheers for that - that's extremely helpful. I do wonder if it's possible that the heater could be clogged as you say. It still blows hot, but not quite as hot as I remember it used to be, plus there is a lot of silt in the cooling system.

The reason I'm worried about the radiator cap is because this one has the valve on the bottom that springs shut - the previous (bad) cap had the valve dangling open. When I mistakenly put an unvented one on my XJ the coolant recovery system didn't work at all. I might try swapping the one from the XJ for a while to see if that helps/

The only question I can think of - if the heater is blocked, what reason is there that this would cause air to be in the system at the vaporiser? Is it simply because a blocked heater core is difficult to bleed?

I know I'm asking a lot of daft questions about this at the moment - it's really bugging me and I'm struggling to get my head around it!

[ommony]

Yeah, that's my thinking, anyways -- that the blocked heater matrix traps air any time your coolant gets low or you drain the coolant/etc. The heater matrix is usually a spot where air gets trapped ANYWAYS (hence why a lot of people recommend havin the nose of the jeep up in the air to help get air out), so if there's poor flow through it, surely that would make bleeding air out even more difficult?

Like I said, may not be your problem, but it costs nothing to flush the heater matrix and re-route some hoses and it MAY help you out. Worst case scenario, it does nothing or just makes the heater blow a bit better. I always like to try the cheap/easy stuff first, where possible, before spending loads of money on replacement parts trying to chase a mysterious issue -- I've been down that road before and spent £hundreds before realising there was a loose earth cable, or something like that.