Reasons for Head Gasket Failure

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davek-uk
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Reasons for Head Gasket Failure

Post by davek-uk »

Being a home mechanic (I use the term loosely) I have limited knowledge of head gasket failures but covering the mileage I do (25k-30k pa) with old cars means I have had a few fail.
In everyone's considered opinion what is the most common causes of head gasket failure?
Thinking back, I cannot remember ever having removed a gasket with obvious damage (other than rust around the waterways) so I'm wondering if they usually fail when the head flexes due to the bolts stretching – helped in many cases by poor torque settings and/or overheating.
If that's the case, could you prolong head gaskets by replacing the head bolts at regular intervals – or just re-torque the originals?
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Post by beezer »

With diesels, the most common cause of gasket failure appears to be overheating by whatever means. The diesel combustion process generates a lot of heat and if cooling is insufficient the head suffers (driver's head and cylinder head).
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Post by G4EIY »

Hi Dave,
If you look at the "Hints and Tips" section, I have put on a couple of items, which is purely from problems on the Citroen diesels that I have owned.
This may help you to understand why good cooling is so essential.
Cheers
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Post by tomsheppard »

PRM and I are convinced that there are two main reasons for the failure of BX Diesel head gaskets. Once the engine has done 100,000 miles, the radiator efficiency is usually reduced to the point that the gasket is vulnerable. We'd counsel anybody who'd listen to have the radiator flow tested by professionals at this mileage and be prepared for bad news.
The second reason is the tendency for fan switches to become arthritic with age, causing the cut-in temperature to rise. This component costs about the same as an oil and filter change so I swap it out as a matter of course when I buy a car. I'd then expect to get 80,000 miles out of it.
The BX has a fairly weak coolant filler cap, too, so my five point plan to save the engine is as follows:
Flow check radiator, new stat, rad cap, fan switch, then refill antifreeze mixed with deionised water.
Jon

Post by Jon »

I'd agree with that.
I would add that a silted up radiator is one of the most common causes of diesel h/g failure. One of my checks at every service is that the rad is not cold at the bottom, hot at the top; big trouble otherwise!
Regular coolant change then bleeding; using good quality antifreeze helps guard against a silted up cooling system.
Jon

Post by Jon »

3 replies within 60 seconds!!
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Post by beezer »

It is a hot topic!
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davek-uk
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Post by davek-uk »

So the consensus is cooling problems so far.
I agree. The AX suffered a spate of hose failures that led to its most recent head gasket failure. But it’s first failure with me was due (I believe) to poor workmanship of the previous owner’s mechanic who had done the head gasket a few months prior to my purchase.
Does this mean that with a good cooling system you’ll never get a gasket failure?
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Post by tomsheppard »

YES! (Mine will now fail on the way home of course!).
With the proviso that the head doesn't crack, that you keep enough oil in it, you don't suck up a load of water in the inlet tract and that an injector doesn't fail, filling the cylinder with fuel, that the block doesn't freeze up, etc. etc. but generally speaking, YES!
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Post by tomsheppard »

And before Bernie gets in that the aliens didn't leave the probe in...
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Post by bxbodger »

Its not helped by that peculiar French foible, not fitting temperature gauges!!!!
Head gaskets very rarely, if ever, fail by themselves- what happens is that the engine overheats, the head, usually having a different expansion rate to the block, then warps, then the gasket goes, and without a temp gauge it all happens before you even know it.
Fit a gauge, watch for abnormal behaviour, and you shouldn't have any bother.
A lot of damage is caused by people not stopping and turning off immediatly, but thinking that they can get home before all the water runs out- in the old days of iron heads and blocks, you may have got away with it ( but my old Marina didn't.........) but not now.
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Post by P 2501 »

I think everyone has got it spot on here.
I don't believe that the xud (or any other engine) has a particular habit of blowing head gaskets. It is the ancilliary components already mentioned like the lack of temperature gauge,silted up rad,dodgy fan switches etc that contribute to an overheat - the prime cause of a blown HG.
Use a top quality coolant and DI water and check the fan operation and rad condition occasionally and this together with an eye on the temp gauge will result in an everlasting head gasket.
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Post by TomH »

When mine went, it only overheated <u>afterwards</u> as a result of rapid coolant loss from somewhere in the head (yet to investigate why or where specifically) which made me stop. I never let it get hot enough to warp anything as I recognised the symptoms straight away from when it happened before. I suspect poor fitting of gasket before or something, but being 10 years old and over 100k I suspect the radiator is not as good as new.
I don't trust the water temp guage as it is useless if the water is not circulating properly and an oil temp guage would be mighty handy too!
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Post by prm »

Dave, I agree 100% with previous replies regarding the reason for head gasket failure, is mainly due to faulty cooling systems.
After experiencing problems with 16v and recent posts on diesel BX head gaskets failures, most with mileage above 100k.
Removed and bench tested rads, fan switches and senders from both diesel and petrol models all around 100-130k
Found senders and rad thermo switches were more than arthritic as Tom mentioned. Some operating 6-10C above the stated ratings. Removed radiator side tanks and found core restriction very similar to Brian's rad picture in Hints and Tips.
There's approx 8-10C difference between thermostat and rad switch locations and with a faulty/intermittent thermo switch, head coolant temp is constantly running high and approaching boiling point before fans cut-in on slow speed, with no indication from faulty warning light senders.
The only other point I would add to previous recommendations would be a chemical rad flush every 30-50k on any engine above 80k. For the cost of about £35 for thermostat, sender, thermo switch and antifreeze, beats any head gasket replacement. Always used a 50% antifreeze mix with no problems. Maybe I'm expecting a hard winter !!
Peter
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Post by prm »

One additional point obtained from a hose manufacturer that may help avoid a few failures/breakdowns.
Applies mainly to coolant, but to a lesser degree, on oil and air intake hoses.
To detect general internal condition without removal, irrespective of mileage.
Squeeze all hoses-- Thumb and index finger -- both hot and cold, on the centre section of any run, to obtain a guide to the general resistance felt on hose construction. Then apply approx the same pressure along the entire length, paying particular attention to the first four inches from any fixing point. Any major difference, to renew hose They found over 85% of all hose failures occurred within the first 10cm. Remainder due to friction points, damage and poor installation.
The weakening in this particular area, being due to, high static charges within some cooling systems, Differing temps/material at connection points and flow characteristics. Degrading internal construction.
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