Please don't let it be the Head Gasket

Mariner · Post by **Mariner** » 16 Dec 2006, 19:21

CITROEN ZX 1.9D
1995
I would like some advice on whether anyone thinks I've got a blown head gasket.

Driving to work the other morning after recently passing an MOT, I noticed the water temp shot up to over 100 Deg C.

I obviously ditched the car not wanting to damage the head.

Later that evening carefully drove it back home and noticed that the temp stayed cool for about 10minutes before rapidly (seconds) shooting back upto over 100DegC. There was absolutely no heat coming through the blowers

Today I put in a new thermostat, flushed radiator and engine with hosepipe then refilled with water using header and closing the three valves in turn (bottom up). I then did what Haynes said and run until the fans kicked in. The temp never reached more than 70 Deg C so the fans didn't ever kick in.

I also noticed that the heater matrix pipes never got warm.

I then took it for a run where it stayed cool until heavily revved and then shot upto 100Deg C within seconds.

What's going on?

Please help me.

jeremy · Post by **jeremy** » 16 Dec 2006, 19:46

What's the condition of the bottom hose like? BX has a very long one which can go soft with age - and I think I had it happen. The car was fully laden (Estate TD) on a very hot day (30 or so) and I booted it up a hill when suddenly the lights came on - pulled up - all seemed OK - didn't even seem hot - but fans were running as though it was going to take off!

There was no water loss - and its still running nicely today - and I think it sucked the bottom hose flat and cut off the supply!

If your head gasket has failed and is causing cooling problems - it must be leaking between a cylinder and the cooling system - which means bubbles in the cooling system, combustion smells, oil (unburnt fuel), pressurised hoses and so on.

The problem with the circulation problem theory is that if the system was blocked somewhere (no water pump impeller, bottom hose problem etc) I would expect the engine to warm up normally (after all there's little circulation with the thermostat shut) and just to go on getting hotter. However I suppose the sensors are a bit on a limb and water may not get there easily until provoked by some local boiling.

Post by **Peter.N.** » 16 Dec 2006, 19:51

The cause of a cold heater and hot engine is almost always lack of water. Cold air from the heater is an early warning sign of a drop in coolant level. The thermostat would be the first port of call as if it stays shut the water will boil and be ejected from the overflow. If it is still overheating with the new one in the next most likely thing is that the radiator needs replacing, especially if the car has done much over 100k. When you ran it up to 70C, did the radiator get hot at all? if so, it shows that the water is circulating OK. The heater is probably full of air and wants bleeding. A faulty head gasket will not normally cause overheating, but overheating will cause a faulty head gasket!

Mariner · Post by **Mariner** » 16 Dec 2006, 19:56

Peter,

When running upto 70 Deg C I felt the radiator and it was cold.

Does this mean radiator or does it mean head gasket.

How can I check if it is the radiator without buying a new one?

jeremy · Post by **jeremy** » 16 Dec 2006, 20:56

The radiator is a crossflow radiator as used on most modern cars. Old fashioned ones were vertical flow with tanks top and bottom - and any dirt and sludge would collect in the bottom tank where it was relatively harmless.

On crossflow radiators the thing is turned through 90 degrees - so the tanks are on the ends - and sludge and dirt collects in the tubes - generally from the bottom up. You can loose a few tubes and never notice it - and what normally happens is that they gradually block generally from the bottom and there is no problem until one too many clogs.

However problems normally start occurring at times of stress on the cooling system - ie hot weather, towing trailers, long hills . . . and the thing will function normally for a while longer if treated gently.

I don't think the radiator is your problem as

You have flushed it (not conclusive I agree - but you would have noticed if there was no flow at all)

If it was totally blocked the thing would warm up normally - and basically it would behave in the same way as with a permanently shut thermostat. - In which case it would warm up normally, the heater would work and it would just get hotter and hotter and hotter!

Post by **RichardW** » 16 Dec 2006, 21:00

If it is the head gasket, you will get some or all of: bubbles in the coolant with engine running (this should have been obvious when you were running the engine to bleed the system - you are looking for a fine stream, not the big bubbles as the air pops out); pressure staying in the system (release of pressure if you take the cap off when the engine has cooled overnight); pressure very quickly after a cold start (refit the cap after the above test, then start the engine run it for 30s or so and check again for pressure). Any of the above then you can probably condemn the HG. Might also exhibit steamy exhaust and oil in water or water in oil (although usually the diesel HG goes by loosing pressure to the coolant). If the rad is blocked then it will tend to have patchy heat when the engine is warm - however - this is unlikely to happen suddenly.

I think your water pump has given up the ghost. There was a post on here a while back very similar, new rad, HG etc, and still problems - new water pump fixed it though....

Mariner · Post by **Mariner** » 16 Dec 2006, 21:09

Richard,

Why do you think it is the pump and not the head gasket?

There were bubbles during the header tank stage and these were big and constant.

If it is the head gasket why would I not get heat in the car cab?

Also what exactly causes the coolant to overheat if the head gasket is leaking?

Ta

jeremy · Post by **jeremy** » 16 Dec 2006, 21:20

Water pump - if the impeller drops off you will have no forced circulation - and so no water would go through the heater. The curious bit is why the temperature gauge responded slowly but there was probably eventually some circulation due to hot water rising.

What usually happens with the head gasket is that the high pressure gas forces the cooling water out and what's left boils. Gas against the engine doesn't allow for proper cooling etc and eventtually it boils generally due to a break in the water flow.

Post by **Peter.N.** » 17 Dec 2006, 09:04

I have never heard of a water pump failing on an XUD, but from your symptoms it, as Jeremy says, certainly sounds a posibility. A faulty head gasket wont in itself cause overheating. If the pump is working, you should be able to see the water circulating in the header tank, if it isn't the water will be still but with bubbles. If you take a heater or radiator hose off with the engine the water should be forcibly ejected, but with no circulation, maybe, water pump.

Mariner · Post by **Mariner** » 17 Dec 2006, 10:24

I have checked this morning and there is definitely water circulating back into the expansion tank when the engine's running.

It's sort of squirting in through rhythmically.

What can I check next?

jeremy · Post by **jeremy** » 17 Dec 2006, 11:49

Was there much pressure in the system when you opened it? What did the water smell like? Is there any oil in the coolant?

The general cause of the heater not working in these circumstances would be an air lock.

If the engine overheats it will produce steam only which will condense and not introduce gas into the system. (obviously if it boils for a long time or very hard and blows out loads of water things may be different) What I'm getting at is that if there is gas in the system it's probably come through the head gasket - or a crack in the head. Its unlikely that gas can get into the system from elsewhere as the system is pressurised which means that leaks will be water outwards rather than gas in.

This doesn't sound like a cracked head - as the problem had been reduced by 1995 - and often minor cracks seal adequately as soon as the head gets a bit warm - and so can be unnoticed for a long time.

Mariner · Post by **Mariner** » 17 Dec 2006, 14:24

Update

There are no debris type blockages in the system as all three bleed points eject water when header is fitted to radiator fill point.

However, with the engine running I removed the two heater matrix hoses and there was no water reaching the heater matrix at all I then refitted. I then removed the pipe that exits the head right next to the fuel filter housing and this wasn't showing a water flow.

I undid the engine oil sump nut and drained off a litre of oil, there was no evidence of water in this oil or any emulsified deposits.

There was a bit of white smoke from the exhaust upon starting but I am sure I've seen this before.

The system does appear to get pressurised quite quickly but....

Why no water in the engine oil if head gasket?

Why is there no water reaching certain parts of the circuit, pump or is this normal.

If the pump has failed and the water is effectively heating up in the head area and then boiling very quickly, wouldn't this also create pressure?

FINALLY.....How can I definitely check that it is the head gasket or water pump with them both being so closely linked in terms of failure symptoms?

slim123 · Post by **slim123** » 17 Dec 2006, 14:44

To be quite honest, if the temp gauge shot up to over 100 then the head gasket will most likely have gone and possibly even the head has cracked.

If the cooling system has air bubbles in it when running the only place it will come from is the cylinders.

As the pistons go up they create a lot of pressure before the bang to make em go back down again, if there is the slightest weep between the combustion area and the water jacket, this pressure will escape into the water jacket and show up as bubbles in the header tank. When the rad cap is tight it will create pressure, making the hoses go rock hard.

The reason that there is no oil in the water is because the head gasket is sealing fine in that area.

I think that you will have to grit yer teeth and get the head off

whilst you are at it you will have the cam belt removed so if you suspect that the cause was the water pump, change it too, they are only about £25 and will only take about 1/2 hour extra whilst every thing else is out of the way.

I would also suggest that when the head is off, you pop it into someone who can pressure test it for you. Personally I would never change a gasket on one of these engines without getting the head tested.

Regards
Slim.

Post by **Peter.N.** » 17 Dec 2006, 19:31

This doesn't account for the lack of water at the heater hoses, have you tried pouring water into the header tank with the hoses off? If the head gasket is leaking the cooling system should still function OK, unless there is so much pressure that it's blowing the water out. When you fitted the thermostat was it possible to fit it the wrong way round? I know it is on some cars, the capsule should be toward the head.

Mariner · Post by **Mariner** » 17 Dec 2006, 21:20

Slim,

I agree that if overheated for whatever reason the head maybe damaged.

I know I'm hanging to the possibility that it may not be the head gasket so I don't have to spend £600 getting it done at a garage but....

let's just say it is the water pump that has for some strange reason failed - wouldn't this also create pressure in the system?

- Peter, I did fit it the right way round and I also tested it in boiling water before fitting.

My difficulty is that now I have now way of knowing for certain it's the head gasket because I can't get it anywhere. Is there a test I can do at home?