Mystery P38 problem.... Circulation / overheating...

Hi all.
I’ve been lurking for a while, picking up tips here and there, but despite the pages and pages that have been written about P38s overheating, I’ve not found anyone with my exact problem.... so I open the mystery to the collective wisdom of this forum....! I'd posted this in the general chat section before, but got no replies, so moved it to here instead....

A bit of background:
The car is a 2000 P38 4.6 V8 with an LPG conversion.
I’ve owned the car for about 4 years, and despite various problems with the LPG system which were eventually resolved properly last year, I’ve had no major problems until this overheating started.

Probably worth mentioning, I did have a gradual coolant leak that I kept on top of by topping up every couple of days (I was pretty lax about antifreeze though, so it ended up a very weak mix).

I had the car booked in to my local independent garage for an MOT, trying to solve the coolant leak, and some service issues (not a Land Rover specialist, but a very good mechanic IMHO). I could see part of the coolant leak around the throttle housing, so this was due to be fixed....

The evening before my garage-date, the car decided to do a proper overheating number on me – all the fluid blowing out of the cap. I topped it up and eventually got home by stopping periodically to let it cool down.

At the garage, the initial diagnosis was a faulty thermostat, so this was changed, along with work on the throttle housing. This throttle housing work does seem to have solved the gradual leak.... (NB – dry footwell also), but the car does seem to lack a little power since this work.

Got the car back, a couple of days later, same problem – new radiator this time.

A couple of days later, same again - new water pump.

Losing patience, and running out of money, I decided to have a go myself. I’ve re-done the thermostat, and re-routed some of the LPG plumbing to reduce the height of the pipework relative to the header tank, and installed a bleed valve on the LPG pipework at a high-spot.

My work seemed to have solved the problem, lasting a week this time, but the old problem has returned. A summary is this:

• I’ve tried my best to bleed the system completely, but I can’t be certain...
• New radiator.
• Two new thermostats.
• New water pump.
• New pressure cap.
• Problem seems to be intermittent.
• Top hose pressure seems ok until I get to the point where the coolant is boiling over – then it is very hot and very firm.
• Bleed pipe from top of radiator isn’t blocked.
• It has got worse since the work on the throttle housing... coincidence...?
• Power seems down slightly since the work on the throttle housing.
• Coolant has been tested negative for combustion gasses, though I have to say, the fault never appeared whilst the car was in the garage (typical!)
• The overheating only seems to occur when the car is travelling – rather than being stood on tickover.
• No sludge in oil.
• No obvious oil in coolant.
• It has spent a lot of time over the last few months with a very weak mix of antifreeze.
• Usually, when it is overheating, the middle of the radiator is cool.
• Passenger footwell is dry.
• I’m in the UK. Weather not particularly warm or cold, and doesn’t seem to be a factor either way.
• Even when the car has been ‘behaving’ over the last week or so, when looking under the bonnet immediately after going for a drive, the pressure cap has been hissing gently – releasing gas.
• I can’t think of anything else.

I suspect it is a circulation problem / airlock, but I can’t work out how or why or where – or more crucially, how to test or fix.

I suspect some will start suggesting slipped liners.... I’ve seen it suggested many times, but I’m unsure exactly what the symptoms of that would be? I don’t claim to be an expert, but does that fit with being intermittent? Also, how would it explain my cool radiator? I did read only today about a bloke who’d had his liners done, then got his car back and it still overheated...!

I've also remembered - since writing the original post - I remember hearing a 'tinking' noise just before it overheated last time. I don't recall hearing it any other time. Also, the first time it overheated after the 1st new thermostat was fitted, there were copper particles in the header tank - looked a bit like some copper slip had got in there....???

Sorry for the long post, but I’ve tried to be thorough.

Any help, suggestions, or answers gratefully received!! – I’d especially like opinions about whether the throttle housing work could have anything to do with it.....

Many thanks in advance!

Did u check the viscous fan?copper inside might indicate that the po added a seal (ironite kseal) and when u added anti freeze it has dislodged it.with lpg i can't tell u a thing.but normaly when tstat hoses leaks cap water pump vc fan have been replaced and overheating is still present,it is an indication of slipped liners or blown hg.remove the plugs and check if they have been steam washed.good luck

Ok, back again. Been away for a week, so not managed to get under the bonnet until today....

I've checked all the plugs, and all seem normal - no evidence of steam cleaning. I'm guessing the viscous coupling is fine given that the rad seems cool even when overheating. Anyone any thoughts or suggestions?

doesnt the fact that rad seems cool when overheating ring a bell rad should be hot no rad actually cools coolant down to luke warm when driving it just stops it going above whatever stat opening is say 86 degrees or around ,either stat isnt opening or rad isnt colling as should be hot all over cooler areas on warm engine indicates no coolant flow through that area ,which could be thermostat ,rad or low coolant level

I'm not sure it rings a bell, but it certainly has me confused....:I've done new rad, 2x new thermostats, attempted fastidious coolant system bleeding & filling, and coolant level is fine (until it overheats and blows out of the cap!) though possibly rather diluted at this stage.

I suspect a circulation problem, but don't know how to pinpoint it....

sorry hadnt read the rest, but statement still stands rad should be hot if system okay ,new rads can be faulty ,id be thinking about cracked block ,gas entering system from vapouriser ,head gasket

So gas can get in via the LPG vaporiser?? Would I be able to smell that in the coolant header tank?

I guess it is the lesser of the evils.... I can reasonably easily bypass the vaporiser for a while to test, so I'll do that later....

If it is a head gasket or cracked block, how can I tell?

you could just connect coolant pipes together and bypass vapouriser ,its not common but have come across it a few times , can normally smell the gas in header tank ,but i find lpg smell around engine to confusing to be 100% so test is best,headgasket will be slight so may not show up on compression test ,cracked block unless catastrophic wont show or have indicators other than head gasket fault ,i have stripped blocks to prove they crack by removing liners ,and tested blocks by removing heads blocking water ways filling with hot water and pressurising with air ,it shows with leak between liner and block but only when hot usualy hence the hot water often would show with air when cold

I know nowt about the LPG system, but would have suggested getting a sniff test done at a garage. If negative you can then discount slipped liners h-gasket etc. Seems thats been done.
How long were you running with no anti-freeze? Coupla weeks shouldn`t have done much harm, but remember it acts as a corrosion inhibitor too, not just to stop freezing.
You say middle of rad cool? If top or bottom is hot with middle cool then looks like a blocked rad. Have you tried taking hoses off rad and giving it a good flush? Over -heating could have dislodged some gunge, that`s now lodged in the rad couldn`t it? The copper coloured stuff that came out? Possibly rusty powder stuff?

Run it on petrol and see what happens as faulty vapouriser
Can cause weird problems

is your new cap faulty?header tank cracked?what are your top and bottom hoses like? check the internal condition of the hoses,ive had the internal lining of a hose collapse and prevent water circulation.any doubts change them.hope this helps,a few more things to eliminate

Iv had the same sort of problem recently overheating with no gas in the header tank no oil water mixing.
I tested the rad take out and lay it flat on the foor poor water in one end and it came out the other fine so i decided it eas fine. Then i teasted the stat by pouring water starght out the kettel in one end it took a couple mins but it came out the other end. So that brought me onto the vicous fan teastes that by getting a dum child to put his arm on it and it dint stop. Then came the water pump ripped that out and desided that was fine to no movment on the impeller. The bottem of the rad wad still cool when the top was hot. So i went back to the stat after rememering how long it took to open at kettle temp close the boilling point. So i drilled some holes inside of the stat and bent it till i could ser though it. Back to gether and privlem solved.

fix it,do you work in one of those Indian call centres,English please:hysterically_laughi:fish:

Ok, I've done a bit more....
- I've completely disconnected the LPG vaporiser and capped off the coolant pipes for now.
- Having inspected the hoses, one looked a bit knackered - the one with a 'U' shape coming off a t-joint - header to thermostat I think... Anyway, I've changed that (once I got it off, it seemed ok internally, but changed it anyway.

Car has run ok for a few days on very short 'test-run' journeys. However, it overheated today on the way back from (ironically) going to buy some coolant of the correct type...!

Are thermostats a weak point on P38s? A couple of times I've felt the rad when it is overheating, and it is cool in the middle, but red hot at the top and on the engine side of the thermostat.... A few other times, I've stopped and checked the rad when not overheating, and it seems to be working just fine. Its as though the thermostat isn't opening early enough, but all is ok once it does open.

On a different thread, someone suggested Radflush to clean out my system of any blockages.... is this a good idea? Bearing in mind I've got a new Rad, so if I do have any blockages they're probably in the engine somewhere..... Is it worth a shot? Is there a downside?

Stop me if I`m wrong, but,
If the top of the rad is hot then the thermostat must be opening to let hot water there.
If the rad middle is cool then there can be no (or little) flow.
So either there is a blockage OR water pump fubar-ed ??
Any more comments?

My interpretation is that the top of the rad can get hot because of the water coming in from the 'top hose', but can't circulate properly through the rad until the thermostat opens...

Water pump is new. Rad new.
Confused.

I'm increasingly thinking it must be a failed HG, but I can't shake the niggling about the seemingly poor circulation, and I've no 'proof' that it is a HG problem... or am I just in denial about the inevitable?

I had something very similiar, however the heating in the car also stopped when the engine overheated, do you have that problem?

When you say "overheating" exactly what do you mean?
Temp gauge goes into red and stays there?
Steam?
Temp gauge goes above half, then drops back to normal?
Is there always a big temp difference between top/middle of rad?
How long are these test runs? Enough to get up to normal working temp?

sionnach said:

I had something very similiar, however the heating in the car also stopped when the engine overheated, do you have that problem?

Click to expand...

I'm not sure.... I did notice a lack of heat once, but I can't be certain it was every time... You said you 'had' a similar problem.... how did you solve it?

gtland said:

When you say "overheating" exactly what do you mean?
Temp gauge goes into red and stays there?
Steam?
Temp gauge goes above half, then drops back to normal?
Is there always a big temp difference between top/middle of rad?
How long are these test runs? Enough to get up to normal working temp?

Click to expand...

Test runs are long enough to get up to temp, but I've been cautious about how far from home!! Certainly a few good test runs in there - if often 'goes' at about 2 miles from home.

The overheating currently manifests itself as needle going from solidly in the middle to rapidly rising into the red & light coming on. Under the bonnet, the cap is blowing water all over the place, lots of liquid and steam coming from the cap threads and the overflow pipe.

After a short wait, temp guage drops back to middle.

There is usually a temp difference between top and middle of rad when overheating, and usually a very distinct temp difference on either 'side' of the thermostat.

Just to answer a couple of qus from a previous post.... no splits in header tank, no idea if pressure cap is faulty, but it seems to be doing its job.... up to a point! How tight should it be on?

to test if lpg vaporiser is faulty simply turn off gas at tank and run on petrol if problem goes away bingo.