Problem with 406 TD (XUD) 97P reg, 100K miles.
Losing small amounts of water, doesn't overheat, water not dirty. No visible signs of leaks when stationery, radiator look okay.
Did a simple recommended test - engine running, expansion tank cap off, can see small bubbles in the coolant expansion tank.
Garage has performed a pressure test and has said "makings of cylinder head gasket leak". Cost to fix £400-£500.
Are they correct or could it be just a unseen leaking pipe, leaky temperature sensor, etc?
Any help would be useful.
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was that a pressure test of the cooling system or a compression test of the cylinders?
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I fear they are right. Try taking the cap off when the engine is cold (having not removed it since it cooled down!) - if it goes hiss it still has residual pressure and the HG is knackered. Price sounds about right. On the other hand my Citroen BX TD always lost a bit of water, but I didn't know about the bubbles / cold pressure (always had some cold prssure too) - and it kept going for 70,000 miles (1l of water about every 15k miles). Finally got bad enough to need the head gasket doing at 135,000. Then I sold it, so I don't know how long it lasted after that!
Richard
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was that a pressure test of the cooling system or a compression test of the cylinders?
Think it was a pressure test of the cooling system.
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Richard W,
You said: "Try taking the cap off when the engine is cold (having not removed it since it cooled down!) - if it goes hiss it still has residual pressure and the HG is knackered."
I agree that long-standing residual pressure in the cooling system is a symptom of leakage between one of the cylinders and the cooling system but have never understood for sure why the pressure holds for so long (for several days in some cases, petrol and diesel alike). Any idea?
ps. Thanks for giving access to your Profile - others would do well to copy!
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Hmm, never really thought about it, just accepted it! I'd imagine it goes something like this: The cooling system on modern cars is sealed, with a pressure cap set at 1 bar gauge. If you are running the engine with a HG leak, then it will pressurise the cooling system untill the cap just lifts relieving the excess pressure (you will reach steady state where gas input = gas output with cooling system at rated pressure of cap. Once you switch off the pressure starts to drop as the gas and liquid cool down and contract. In a car with no leaks you haven't added anything to the system, so it will return to where it was last time it was opened (eg no pressure) - and this will happen when it has gone cold. On a system with a leak you have added gas to the system, so it will remain under pressure, even when it's gone cold. The only way for this to escape (the temperature contraction will drop you below the set point of the cap) is back through the leak in the head gasket. It is always possible that the 0.5 barg (or so!) pressure remaining in the cooling system is not enough to push the water back through the hole in the HG, so the pressure stays. Don't forget the cylinder side pressure is 30 - 40 barg pushing gas out into the cooling system.
A good description? Probably not, but I think I know what I am talking about!!
Richard
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Richard, I think you have solved it! Thanks for this and your other very useful contributions to the forum.
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I had a water loss problem with two 406s, one with the ordinary turbo-diesel and one with the hdi diesel. In both cases it turned out to be a very slight leak from the radiator, both replaced under warranty. Although it may very well turn out to be a head gasket I'd suggest getting the rad thoroughly checked out first.
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I had a water loss problem with two 406s, one with the ordinary turbo-diesel and one with the hdi diesel. In both cases it turned out to be a very slight leak from the radiator, both replaced under warranty. Although it may very well turn out to be a head gasket I'd suggest getting the rad thoroughly checked out first.
Radiator is the original and looks in good condition. No obvious leaks since no drips on the ground after car has been driven. Have also noticed that the engine temp never rises above expected 80C.
I suppose a compression test will verify whether it is a gasket leak or not?
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Update - took car to another garage this morning. They had a good look and didn't think it was the gasket. Said it could be a minute hole in hose or radiator etc, but it could take hours to find it.
Advice was to just leave it alone as there is no overheating, no oil in water, no mayo in oil, no misfiring etc. , but to keep an eye on it. Plus it has ran okay for the last 6 months and 7000 miles.
Saving £400-£500
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I have a 405 with what sounds like exactly the same problem. I found where the water was leaking to when i replaced the sump. With the sump off everything was fine. Until i turned the engine very siightly. A few drops of water started to trickle down the cam belt end cylinder. I presume the engine always stops in a position where the water runs out into the cylinder and not the oil. The oil is fine.The water leak is invisible. There are small amounts of bubbles with the engine running and rad is topped right up with cap off. There is always a slight pressure releif when taking the rad cap off when cool. Also it is getting worse to start, maybe from water sitting on pistion. It has been like this for 3 years, very slowly getting slightly worse.
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