Help: Coolant System Pressurised - Radiator Cold - Top Hose Hot

[ChrisChaos]

Hi all

I’m having problems with my 1999 Td5 Disco’s cooling system which I can’t seem to fix, (or diagnose correctly for that matter)

The symptoms include a build up of excess pressure that causes the top hose to swell and become very hard and not easy to squeeze at all. Even after being left overnight to fully cool, most of the pressure is still there.

Not only that, but the pressure causes the coolant in the expansion tank to disappear until the cap is released, at which point the coolant appears to rise from the depths to nearly where it should be.

While under the highest pressure a little coolant is forced from the radiator lower hose junction despite being tightly done up with a jubilee clip. (there’s a LOT of Pressure built up to be sure)

The top hose gets nice and hot as it should do, but the radiator itself stays cold all over, so it seems obvious that the coolant isn’t circulating as it should. The lower hose and thermostat don’t get hot either.

Heater works fine, the temp gauge sits bang in the middle where it should be once it’s warmed up, though I think it does seem to be taking a little longer than usual to get warm, but that could just be the colder weather that we’ve been having over the last week or so.

I’ve replaced the coolant pump, the thermostat and the expansion tank cap already.

There’s no oil in the coolant and there’s no creamy gunk in the rocker cover either.

Looking in the expansion tank with the engine running there’s no coolant being forced up from below as far as I can tell, the only bubbles in there seem to be a result of the coolant being pumped back into the tank via the small tube that comes from the top of the radiator

The only other thing of note is that on removing the radiator to flush it through I saw a wet rusty/muddy patch just on the weld where the two metal pipes, (the coolant rail?) are joined side by side just below the radiator, I gave it a light scrape to clean and coolant started to run in a thin stream from a small hole. Not sure if it was leaking a little bit from there already but it could have been but at a much slower rate than before

I’m at a complete loss as to what’s going on here, worried that it’s a cracked head or head gasket but no oil in water, no water in oil, runs fine, no smoke black or white from exhaust.

Anybody had this same combination of symptoms? Excess pressure, coolant forced from expansion tank, only to quickly return when cap removed and cold radiator when temp gauge shows normal and top hose hot ‘n’ swollen?

Any help or ideas please

[minimaquinas]

i had the same on a mitsubishi l200

and it turned out to be the head that was the end of the mitsubishi run for me i went back to driving my defender

[robertspark]

Besides the obvious head gasket....

Have you done anything to it reciently? (belt replacement? , coolant change? etc etc).

Is the belt fed round the water pump the right way (under it.... once saw it done the wrong way on a serpentine belt rover v8 engine.... and that suffered from overheating issues I know that one was easy to do, but the water pump on the serpentine rover v8's runs the opposite direction to the v belted rover v8's.

[RedLineMike]

Curious one, has it had the power steering pump replaced? Friend bought a td5 that was over heating & it turned out to be fitted with a 300tdi pump instead of a td5 one which in turn, wouldn't drive the water pump

[RedLineMike]

@robertspark are you aware the power steering pump drives the water pump on a td5

[robertspark]

@robertspark are you aware the power steering pump drives the water pump on a td5

no, sorry I'd await someone else with TD5 experience.

I must admit it's the wrong fuel for me and have zero experience with a TD5 engine, but thought it my comment above may be worth a quick bonnet up check on the belt direction.

but given diesel is a compression ignition fuel, with much higher cylinder pressures that what I'm use to with a petrol, a head gasket is still a high potential cause, but it's worth checking the other obvious bits too that have little time or cost implication, before whipping a head off.

Thermostat been replaced recently? (can it be put in the wrong way around if it's been replaced?, is it woking? (remove it and test in a pan of water with a thermometer, sometimes useful to drill a small hole in the plate of the thermostat to aide in venting the engine (which can also be the cause of overheating if its had its coolant changed recently as air does not pump well especially if it's trapped in the water pump]

Sometimes the thermostats have a venting hole with a small bobble in it (acts as a non-return valve of sorts), check it's all free.

Air can be a real pain in any engine to vent properly, there is also air trapped within the water naturally which only comes out when it's heated and under pressure to remove the microbubbles.

[Les Henson]

There are several reasons why an engine will over-pressurize. Trapped air, water-pump not driven/impeller sheared off - due to freezing of coolant, thermostat stuck closed, blockage in the cooling system (rad weld, for example). It really depends on how quickly the pressurization occurs. Stuck thermostat will take a while to pressurize the system (as it warms up). Compression loss into the cooling system will be pretty-much immediate - with the header tank cap off, coolant will be expelled straight away with a cold engine. To negate air in the system - drain coolant on a cold engine, start engine and slowly fill again. TD5 self bleeds. Thermostat can only be checked by removing it and dunking in a pan of boiling water, and watch for it to open. Water pump impeller shear can only be checked by removing it.

I would - drain the system, remove the thermostat and check it, remove and check water pump, start the engine and slowly refill the cooling system, check the drained coolant for particles (rad weld, K-Seal, Bars Leak, etc). See how quickly the system pressurizes. If it's pretty-much immediate, then suspect head gasket failure/crack. Head crack test costs typically £100, and if ok, then £90 for a head skim and other parts to reassemble. Early TD5 heads were well known for cracking. Depending on your mechanical abilities - DIY is possible, apart from crack test/head skim.

Les.

[ChrisChaos]

Hi again,

Thanks for all your help and advice guys, it's all loookng like the head or head gasket then

I did the water pump, themostat and expansion tank cap last week hoping that would sort it, so I'm fairly sure it's not any of that.

Followed the 'tank up, bleed screw out, fill coolant' and fitted belt exactly as shown in Rave so all that should be ok as well

Still, looks like I've got a busy weekend ahead, get the head off and pressure tested, (please let it just be the poxy plastic pins/gasket leak) and refit

Anyone got a rough idea of a reasonable price for the pressure test, the only place I've called this morning quoted £70, is that about right?

While it's off being tested, (if it's ok of course), I'll take the oppertunity to get the 2 broken exhust studs removed & replaced and also get them to face the exhust manifold I suppose,

Still don't undersand why no circulation through the radiator though, or where the coolant goes when system under excessive pressure.

It seems to be forced out of the tank which then appears to be empty, until that is the cap's taken off the tank and with a hiss the coolant returns to the tank coming up from the pipe below.

Cheers

[SPendrey]

Welcome back Les, haven't seen you here in a while :-)

[Tanuki]

TD5 thermostat is a moulded plastic 'canister' with 3 large-bore tube stubs that fits in the hoses:

http://www.miamirovers.com/ebay/PEM100990K-MC.jpg

you can't put it in the wrong way round.

Have you checked/replaced the screw-on cap on the expansion-bottle? The cooling system needs to be able to 'breathe' and if the spring-loaded valve in the cap has gunged-up and stuck then the system _will_ go overpressure. A new cap is cheap and easy to try rather than delving any deeper into the engine.

[SOA 93]

First off I have no TD5 experience, however, there is some basic things that applies to most if not all cooling systems. Firstly, cooling systems are designed to be pressurized when hot, secondly the old style radiator cap and the reservoir cap of modern cars are pressure relief valves, usually set to release pressure at about 13psi, so if your system is over pressurising then it sounds like the reservoir cap is not functioning as it should, however, you say that you have replaced it. The hose should not bulge substantially no matter what, perhaps take it off and check it internally make sure it hasn't collapsed internally, if the engine is hot then the coolant could be at 10psi so the coolant pipes won't be easy to squeeze, but that doesn't explain why its still hard when cold.

Is there a correct sequence for refilling coolant on a TD5? Some cars have to be filled in a certain way to prevent air getting trapped.

You don't have to have oil in your coolant or the other way round for it to be the head gasket or a crack, either could just be into the coolant system while the oil system is intact.

My experience with coolant into combustion chamber is a pressurised cooling system when hot with some coolant loss and then when starting, starts -1 cylinder or when very bad an initial hydraulic lock.

You need to do a pressure check cold, On tdi's its easy because they have a 1/2 BSP threaded boss in the top of a radiator, not sure about the TD5, If you can't then you need to take it to a garage or someone that can do a cold system pressure test, pump the system up firstly to over 13 psi or whatever the pressure relief is set to and make sure that works, and then back off to just below the pressure relief setting and then leave it for a while and make sure it is holding pressure, if it has dropped then there is a leak, the good thing about doing a pressure check cold is that without the engine running you can usually see and sometimes hear a leak at 10 psi, I should point out that it needs to be cold as if the engine is hot then the pressure will drop at the coolant cools naturally. Check externally for leaks, if your sure you have no external leaks but are still getting a pressure drop then it could well be internal.

[SOA 93]

What actually lead you to the assumption that there was something wrong with your cooling system.

Your engine is not overheating, its running perfect.

Are you having some coolant loss?

An efficient cooling system shouldn't be hot everywhere while idling and I'm assuming you not grabbing hoses and touching the radiator at 70mph!

So what was not working to make you think you have a problem?

[Boydie]

Just a thought but have you checked that the radiator isn't caput - as in the cores are not blocked ? If as you say the top hose is hot and expanded under pressure I'd guess that there isn't flow, it's not unknown for the radiator cores to become blocked with gunk, if they are and flow is seriously reduced then sometimes they can be cleaned chemically by a radiator specialist and pressure back-flowed to remove the gunk, if not it's a new core.

[Boydie]

BTW if this does turn out to be the problem then if I were you I would be looking at the heater as well, it may also need flushing out.

[Tanis8472]

TD5 thermostat is a moulded plastic 'canister' with 3 large-bore tube stubs that fits in the hoses:

http://www.miamirovers.com/ebay/PEM100990K-MC.jpg

you can't put it in the wrong way round.

Have you checked/replaced the screw-on cap on the expansion-bottle? The cooling system needs to be able to 'breathe' and if the spring-loaded valve in the cap has gunged-up and stuck then the system _will_ go overpressure. A new cap is cheap and easy to try rather than delving any deeper into the engine.

Unfortunately they can be put on the wrong way round. Mine was, by a 'mechanic' when converting my Hippo system.

Was causing problems until i corrected it

Hi all

I’m having problems with my 1999 Td5 Disco’s cooling system which I can’t seem to fix, (or diagnose correctly for that matter)

The symptoms include a build up of excess pressure that causes the top hose to swell and become very hard and not easy to squeeze at all. Even after being left overnight to fully cool, most of the pressure is still there.

Not only that, but the pressure causes the coolant in the expansion tank to disappear until the cap is released, at which point the coolant appears to rise from the depths to nearly where it should be.

While under the highest pressure a little coolant is forced from the radiator lower hose junction despite being tightly done up with a jubilee clip. (there’s a LOT of Pressure built up to be sure)

The top hose gets nice and hot as it should do, but the radiator itself stays cold all over, so it seems obvious that the coolant isn’t circulating as it should. The lower hose and thermostat don’t get hot either.

Heater works fine, the temp gauge sits bang in the middle where it should be once it’s warmed up, though I think it does seem to be taking a little longer than usual to get warm, but that could just be the colder weather that we’ve been having over the last week or so.

I’ve replaced the coolant pump, the thermostat and the expansion tank cap already.

There’s no oil in the coolant and there’s no creamy gunk in the rocker cover either.

Looking in the expansion tank with the engine running there’s no coolant being forced up from below as far as I can tell, the only bubbles in there seem to be a result of the coolant being pumped back into the tank via the small tube that comes from the top of the radiator

The only other thing of note is that on removing the radiator to flush it through I saw a wet rusty/muddy patch just on the weld where the two metal pipes, (the coolant rail?) are joined side by side just below the radiator, I gave it a light scrape to clean and coolant started to run in a thin stream from a small hole. Not sure if it was leaking a little bit from there already but it could have been but at a much slower rate than before

I’m at a complete loss as to what’s going on here, worried that it’s a cracked head or head gasket but no oil in water, no water in oil, runs fine, no smoke black or white from exhaust.

Anybody had this same combination of symptoms? Excess pressure, coolant forced from expansion tank, only to quickly return when cap removed and cold radiator when temp gauge shows normal and top hose hot ‘n’ swollen?

Any help or ideas please

Have you got sorted?

[nodrog]

ChrisChaos,

I can't believe how exactly you have described my problems with a pressurised TD5 cooling system. About 18 months ago I fitted a new head and a radiator so things should be in relatively good mechanical shape. Did you ever discover a solution to your problem - was it a head and/or head gasket problem?

Here's what you said originally:

"Even after being left overnight to fully cool, most of the pressure is still there.

Not only that, but the pressure causes the coolant in the expansion tank to disappear until the cap is released, at which point the coolant appears to rise from the depths to nearly where it should be.

While under the highest pressure a little coolant is forced from the radiator lower hose junction despite being tightly done up with a jubilee clip".

[Kosmav]

Hi Chris, I have the same car and I had the same problem. It was a head gasket matter. I went to local mechanic and just changed the gasket with 200€. The authorized dealer asked me +1000€ for that job...

Now everything works fine...