As some of you will remember, my P38 has been using coolant for a long time. 5+ years. It was also pressurising the cooling system and showing signs of coolant in the cylinders (some of the plugs were stained orange). It has however never actually overheated, so long as you keep it in water.

It seemed to be a multitude of issues, leaks in the engine bay pipework, leaks from the water pump, leaks from the heater core orings as well as dodgy head gaskets.

I took everything apart in the summer, gave it new headgaskets, new water pump, new heatercore orings and replaced every coolant hose on the engine. Removed the horrible T-pieces feeding the LPG and rerouted that to be fed from the throttle heater loop instead. Basically ticked every box in the "fix your P38 v8" hot list...

Except, its still using coolant, and still pressurising the coolant system. The top rad hose is properly solid after the engines warmed up, feels like pressing on a car tyre. I've got a leak on the hose on the inlet manifold that goes to the LPG vaporisor that i cant seem to stop, i've already striped one jubilee clip from tightening it up that much trying to stop it. This morning when i got in i noticed red drips all over the side of the centre console carpet and some contorting later it would appear the new heater core o-rings are leaking.

It seems to be leaking LESS than before, which i guess is something, but i'm getting somewhat pissed off with it now.

The interiors in bits as i didnt want to refit all the plastic trims until i'm sure the leaks are sorted. Its also mouldy and horrible inside as both footwells and the boot are damp... The wife tried to use it yesterday while i was at work to find the child seat was covered in mould-fur. So that had to get stripped down, bleached and put thru the washing machine...

Any ideas beyond getting rid and buying a Toyota?

Hmm, my daughter has a Toyota and there's a number of jobs I've got to do on that now mine is back together.....

If it is over pressurising that will put extra strain on any weak points. It will pressurise with thermal expansion but, without anywhere for the pressure to escape, then once cold there should be no more pressure in there. If you have leaks around a liner or two, that will make the plugs go orange and you have two options, top hat liners or water glass (Sodium Silicate, the active ingredient in Steel Seal).

Water in the footwells is usually rainwater leaking in either through the pollen filter housings or through the screw holes where the plastic plenum is attached to the bulkhead. Take the screws out, lift it up a bit so you can squirt some RTV under the plenum and refit it with new screws. A leak into the boot is either through the rear light gaskets or the tailgate seal.

Yeah stone cold it's still fully pressurised. The head gaskets were in a bad way, but given it's still doing it I guess it has to be a liner leak... I guess water glass is the next option, I don't think I want to spend the money going top hat, I'd rather put another engine in it instead, especially as it also needs camshaft and lifters.

Really need to dig into the plenum and try to figure out what's going on there, is there any photos showing what I'm looking for?

Tailgate seal is really ropey, doesn't fit well and the tailgate rattles when driving. Annoyed with myself that I didn't pull the seal off the vogue that was in upullit, they've had zero p38s since that one went. New ones seem somewhat expensive:(

Do a coolant combustion gas check. If fluid turns a greenish-yellow then it's either liners, gasket failed again, or warped head. Failed liners are a lot less common that many "engineering" sites say. Generally it seems to be the US focussed forums more often !!

Did you check the heads for flatness when you did the gaskets ?

The other thing to check is to see if it still pressurises when running on petrol. An internal leak in the LPG reducer can allow LPG into the coolant circuit and pressurise it. Not only that, but it will also fail a combustion gas check as it will detect LPG, a hydrocarbon, as combustion gases.

However, orange stained plugs does suggest coolant getting into the combustion chambers. If it is cylinders at the ends of the heads (cylinders 1, 2, 7 and 8) then it could be a leak from the coolant passages into the cylinders through the head gaskets but if it is in central cylinders, it can't be as there are no coolant passages next to them. I agree that slipped liners seem more common in the US than here, and the BS from the likes of RPi make it seem far more common than it actually is, but it only takes one serious overheat to cause a leak. The liners don't necessarily slip, when they do you can hear them moving up and down with the piston, but a slight weep between the liner and block will cause it. While it isn't a permanent fix, Water Glass will cure that and keep you going for another couple of years. Plenty of time to source another engine. I bought one for another owner from East Coast Range Rovers, a low mileage '98 4.6, for around £500 including delivery. That came complete with the engine wiring loom so just needed plugging in once fitted. The only difference, as it was going in a '97, was the plugs for the lambda sensors were different so had to be changed.

Pete12345 wrote:

Do a coolant combustion gas check. If fluid turns a greenish-yellow then it's either liners, gasket failed again, or warped head. Failed liners are a lot less common that many "engineering" sites say. Generally it seems to be the US focussed forums more often !!

Did you check the heads for flatness when you did the gaskets ?

It was a completely new (used) set of heads, which i had refurbed. resurfaced, valve seats recut, new seals etc etc. I really didnt want to be revisiting this and so did the job as "properly" as i could!!

The block surface showed some markings which apparently are often a sign of leaky liners (rusty staining near the fire ring) on the two cylinders which have the orange plugs for the longest time (cyl 1 and 3). Cyl 6 also had an orangey plug, which is a more recent development and it too isnt near any water gallery.

I've been running it on petrol this past couple weeks as the LPG garage was out when i last went by, so the LPG is ruled out too.

I do have a spare block, but after the escapades with this one, i'm really not sure i want to pour thousands into it. Realistically by the time i've paid for top hat liners and all the usual refurbishment bits and bobs, i'll be 3 grand into it if not more. Probably money better spent on a BMW i6 of some description!

I'm not really sure where the idea that liner problems are rare has come from... The main issue is caused by core shift in the casting process meaning the cylinder wall thickness is uneven. The issue was so well known Land Rover themselves were X-Raying and grading the blocks in the factory to pick the ones with least core shift to build 4.6's from. The core shift causes thin walls between the cylinder and the coolant jacket. These thin walls can then sometimes crack, creating a path up the back of the liner into the cylinder.

Slipped liners i would say are rare, but thats not the most common failure, the most common failure is simply a crack in the block and coolant getting into the chamber.

I've ordered some combustion leak testing fluid. If its showing combustion gas, then i think i'll throw some steel seal in and see what that achieves. In the mean time, i could live with the completely knackered engine if the interior wasnt disgusting and horrible, so i guess i should focus on that.

One concern is those heater core o-rings... i really cant imagine 6 month old o-rings can have failed? They are 22x2.5mm Viton green seals, 70 shore, ordered from a reputable supplier. I specifically wanted to avoid chinesium in a blue box...

I have always only ever fitted genuine LR heater core O rings, for the difference in price (£5 each against £3 a pair for blue box) it's a no-brainer. It certainly sounds like you have identified the problem and it may be that the O rings are the weakest link so the pressure is causing them to leak. A decent secondhand engine would be the cheapest and simplest way forward, building one from scratch will eat money when you start with fitting top hat liners and then adding up the cost of other components (bearing, gaskets, etc).

Many years ago I needed to replace the heater o-rings & decided to fix the blend & distribution motors at same time, so decided to take dash out. Good job I did because I found a crack where the o-rings seat at the matrix input. No amount of changing them would have sealed it, so I did the Audi core change instead.

Agree with Richard about the o-rings, when my time came I used only original ones. Too much hassle to risk ...

I had a water pump fail, last summer, so I replaced the pump and the thermostat and I was happy that the temperature gauge is now content to sit at the centre position [i.e. dead vertical] whatever the conditions. I happily refilled the coolant reservoir with pink OAT coolant and went on my merry way for a few days, before rechecking the coolant level.

As I had drained all the coolant, I have a 2.5 diesel, and refilled it I expected that there may be a bit of settlement of coolant as all the bits and pieces refilled over time, but I was a bit surprised to find that there was no coolant in the reservoir at all. I refilled it, drove about some more, and rechecked it, again to find that the reservoir was almost empty.

Looking around the back of the radiator, and under the the car I could see quite a bit of coolant lying on various pipes for power steering, oil cooler etc. etc. so I thought the stupid radiator has cracked after the water pump failed and the temperature rose up into the red on the gauge.

So I bought a Direnza radiator and fought to get that fitted. It took a bit of pushing and shoving but went in satisfactorily in the end. Again, I had drained the coolant so I went about refilling the system again. And again I drove about for a couple of days before rechecking the coolant level, and again the bloody reservoir was almost empty. I couldn't find any leaks around the engine, and there was no obvious signs inside the car.

But, I had had the drivers' seat out of the car a few months ago, to fit a new sponge seat base and I had had to pull out the fir tree fasteners from the seat base surrounds. I decided to put them back and while doing so I leant on the drivers' side footwell carpet and felt that it was wet. A closer inspection revealed pink coolant sitting on the carpet, under the heater matrix, and on the drivers' side.

It turned out to be a leaking matrix, so I bought a new one along with the O-rings and got a garage that I deal with to do the refit. I have also just replaced the two idler pulleys, the belt tensioner, and fitted a new fan belt.

I haven't driven the car since the heater matrix was replaced, and I had to drop out quite a bit of coolant to get the viscous fan out, and take off the radiator hoses. Despite what some websites elsewhere say there is no way to replace the pulleys and fan belt without removing the fan and the fan enclosure, no way.

So now I have replaced the idler wheels, the belt tensioner, the fan belt, the viscous fan, the heater matrix, the water pump, and thermostat. All I hope is that the carpet now dries out fairly quickly. One thing though - while the matrix was leaking inside the car I never had the windows fog up due to moisture inside the car. Perhaps because it was coolant leaking and not water.

Pierre3.

A bit more on this, its sat for months not really being touched as its annoyed me.

I found my industrial pressure transducer and display that i'd previously used to monitor oil pressure in my track car while tidying the garage and decided to T it into the cooling system to try and see what was going on.

I sorta expected that the pressure would rise very quickly under load indicating pressure making its way into the coolant system, however that was not acutally what i found...

Starting from cold the pressure was sitting around 0.1bar at idle, and rose with engine RPM's to maybe 0.2bar. As the engine warmed up, this slowly climbed up to around 1 bar. RPMs would push the pressure up, 4krpm would see maybe 1.3-1.4 bar, however it didnt seem to matter wether that was 4000rpm in neutral free revving, or 4000rpm at wide open throttle, it just followed RPM's.

After a couple of miles driving, and a full throttle blast upto 70mph, the pressure seemed to settle around 1.3bar. Full throttle high RPM's peaked around 1.5bar and dropped down when the engine shifted gear.

The "minimum" pressure did seem to slowly increase over the drive, which is perhaps a little unusual, but i only did a couple miles around town. Maybe i'll try for a longer trip at the weekend. Also 1.3bar just idling on the driveway, does feel a little high, though granted i have no reference point. I considered connecting the guage to my other petrol car, but its currently off the road with no MOT.

All just seems sort of inconclusive somehow.

Maybe the engines fine and the missing coolant is just leaks? But that doesnt explain the smokescreen i was seeing with a cold engine in the winter... Oddly i've not seen any smoke from it at all these past two days when i've been testing it.

The pressure cap opens at 1.4 bar so I wouldn't expect to see higher than that for any length of time but they do pressurise normally anyway. There's a lot of coolant in there, about 11 litres, so thermal expansion is going to cause it to pressurise anyway. The thermal expansion of water is 1.00021 times per degree C (presumably the coefficient of expansion of a water/antifreeze mix is going to be roughly the same), so an 80 degree increase in temperature means that you've got 11.185 litres filling an 11 litre space. How that relates to the pressure I'll let someone else calculate.....

What I can tell you is that the top hose gets pretty hard when up to temperature. The important thing is that the pressure goes away once the engine has cooled down. If it does, the pressure is down to thermal expansion, if it doesn't, the pressure is coming from somewhere else like combustion gases finding their way into the cooling system or, if running on LPG, an internal leak on the vaporiser allowing Propane at high pressure into the cooling system.

Smoke in cold weather is often water vapour from the combustion process, far more noticeable if on LPG too.

I'll check the residual pressure later today, it usually does have some pressure left in it though.

those pressures are a bit worrying as the thermostat is suppose to control the temp, at 1.4 bar that's max pressure for the system, the system should be around .8ish bar or so around 9psi is a good pressure to have. do you have temp readings or just pressure as the temps for that pressure would be around 118+ degrees. there is something wrong with the system, you are running around 20psi which is way over the top for the system

The t-stat controls temperature, I’m pretty sure it doesn’t care what the pressure is. Also, IIRC, some OEM reservoir caps relieve at 20 psi, so if the system is showing 20psi when the ambient temperature is really hot and the engine under high load, this might be normal.

mad-as wrote:

those pressures are a bit worrying as the thermostat is suppose to control the temp, at 1.4 bar that's max pressure for the system, the system should be around .8ish bar or so around 9psi is a good pressure to have. do you have temp readings or just pressure as the temps for that pressure would be around 118+ degrees. there is something wrong with the system, you are running around 20psi which is way over the top for the system

Temperatures are totally normal, it'll sit around 90c when driving on the motorway for instance.

I do generally agree though i think the pressure is too high and i imagine its a cracked block.

If i get some time over the next few weeks i'm going to flush the system out with clean water and run some of that water glass stuff thru it, cant make it any worse at this point!

Harv wrote:

The t-stat controls temperature, I’m pretty sure it doesn’t care what the pressure is. Also, IIRC, some OEM reservoir caps relieve at 20 psi, so if the system is showing 20psi when the ambient temperature is really hot and the engine under high load, this might be normal.

My cap is rated 140kpa, so yeah, 1.4bar. I suspect your right, the cap is probably venting off extra pressure and it ends up just sitting around the 1.4bar point once up to temp.

water will boil at 100dec to heat water above 100 dec you have to increase the pressure. the pressures that are mentioned are in the area of the temps i mentioned. you cannot have one without the other, we are delving into the area of latent heat to increase the pressures above boiling . operating temps are around 85 90 dec running temps , if you remove the cap at that temp the temperature will go from 90 dec to the flashing point or instantly boiling as it is the pressure that stops it from boiling. without the pressure the cooling system will not handle the temperatures. the only way to increase the pressure and not the temps is a cylinder leak of some description, either way it's not good, it's telling you there is something wrong.
PS the thermostat controls the pressure by controlling the temperature.

I’m probably being nit picky but the t-stat controls temperature. It does have an effect on pressure as a result (as a few above posts have already pointed out).

Aragorn wrote:

mad-as wrote:

those pressures are a bit worrying as the thermostat is suppose to control the temp, at 1.4 bar that's max pressure for the system, the system should be around .8ish bar or so around 9psi is a good pressure to have. do you have temp readings or just pressure as the temps for that pressure would be around 118+ degrees. there is something wrong with the system, you are running around 20psi which is way over the top for the system

Temperatures are totally normal, it'll sit around 90c when driving on the motorway for instance.

I do generally agree though i think the pressure is too high and i imagine its a cracked block.

A sniff test for exhaust gases in the coolant should confirm (or rule out) a cracked block.