Petrol engines cylinder head leak

From VW T25(T3)-Tech
Jump to navigationJump to search

Those rubber seals

The rubber seals harden with age, then they don't seal, then the engine starts leaking coolant, then the heads leak more coolant, then the seals go properly and the AA man says 'blown head gasket', then you go to a garage and they don't like the look of it, then the head studs snap when they're taking the heads off, then they call you, then you cry, then you have to find a specialist to get the studs out, or find someone who can supply a recon engine.

Coolant leakage from those rubber gaskets is NOT a sign of head gasket trouble. AA man and non VW garages (also some VW garages without experience) don't understand these engines. The gaskets, as mentioned above, are affected by cold weather. You will know the difference when a head gasket is leaking. I have been running my 1.9DG for almost a year now, 8,000 miles, with a Wynns sealant in the cooling system and it has cured the small leak from those gaskets. I also know of other owners who did the same. The Wynns product is not the same as Radweld, BarsLeaks or the Halfords equivalent and works in a totally different way. I can only speak of my own experience and urge anyone who tries it to follow the product instructions carefully.

Ran ours for about 6 months with a fairly steady leak from nearside. Was much worse over frosty winter and seemed to be better if we ran the van every few days. (Although probably more to do with evaporating it all off than actually slowing it down!) Previous owner had used Holts RadWeld, but all that seemed to do was gunk up the entire cooling system, and make no difference to the leak!

Radweld and it's equivalents are totally unsuitable for these engines and many other engine types as well. It can cause a solid lump to form in the cooling system and cause complete failure. This though is occaisonally due to the way it is added to the system and not following instructions.

Frostbus - since you asked I will tell it as I have had it explained to me by guys who know much more than I do. Radweld and similar products work by producing solids when they make contact with air. Ideally they should only do this when they find a leak and and as the material meets air, through the leak, it forms a seal. Trouble is that it also forms solids when it meets the air at top of the radiator and in expansion tanks. These solids can be pumped around the engine and then cause blockages in narrow passages etc. According to the technical information, Wynns Radiator Stop Leak works differently to traditional materials in that it consists of fine organic fibres that slowly close external holes but do not interrupt coolant flow. They recommend using it as a long term cooling system additive . This may sound like a load of rubbish, but I was originally recommended it by a garage that frequently works on Porsche waterboxers. I also know of three other T3 owners that have been running their engines with it and two of those for over two years. I was a little wary of using it at first but contacted Wynns Technical Dept. and they assured me that their experience with Transporters showed it to be quite safe to use. I would point out though that I have no reason to believe it will repair a split hose, leaking cylinder-head gasket (not to be confused with water-jacket sealing rubbers on a T3), corroded radiator or cracked header and top-up tanks.

Leak from upper cyl. head bolt

Leak from from upper cylinder head bolt

Cylinder-head sealing refurb notes

Laurie: Cylinder heads don't usually blow due to head faults.

The rubber seals blow because they are a bad design and the inner rings blow due to overheating or studs getting tired... also due to bad design. If the inner sealing surface where the metal rings go is undamaged then it is safe to gently lap the barrels back in and if the surface that faces onto the rubber is decent, i.e. slightly pitted, you will find that Elring puts a black, non-etching silicone into the head kits to take out the irregularity. Being that the rubber facing surface on the head is not a compression or a moving part, if the head has any deep pitting there - it is perfectly safe to use something like JB Weld to fill the pits. Then smooth it down and use it. Bear in mind... the barrel facing surface must be undamaged. People often score them when taking the old head rings out and they never seal without machining.

Skimming is possible but care needs to be taken, not only to take the same amount off both inner and outer surfaces but also to make sure that only a tiny skim is taken. I recently had a major re-con in which had been skimmed so much that the tappets, not the screws were touching the valves!

Ghost123uk: - Re:- Replacing the head studs If you have to remove or replace the main studs due to breakage or corrosion you need to know how far in to screw the studs into the crankcase. The answer, as provided by Bigjcc55 who got the info from Elite VW is They don't go all the way home, put them in enough so the shoulder doesn't foul the base of the barrel. But not too far in that the head nut has nothing to grip, do a couple of dry runs with the water jacket seal in place and no push rod tubes to get a happy medium.

A video of the strip-down process by Ken Wilford can be found here:

Case history

feliz: Hello, our cylinder head gasket blew in France (86 watercooled T25 Club Joker 2.1 petrol). Now back in the UK and our local mechanic is not keen on fixing it, but recommends that the second head should be skimmed along with the other when it is fixed, also a latent problem such as the crankshaft could be in need of repair? A

Any advice would very much appreciated. Is this a major job, worth buying a recon engine? On reflection I think I need a specialist to do the job.

Toomanyoys: Your mechanic is a "general mechanic" and prob knows little about the VW WBX engine...

It's not possible to "skim" the heads in the traditional sense and he will soon see that when he takes it apart.. If the head is "skimmed" then the water jacket gaskets will not be compressed enough to seal and he will soon see that when he fills it with water!

If he is an "engineer" then you can skim the head lightly (See Laurie's synopsis above) but the head gasket/barrel seats also need machining to correct it - in practice this is costly and really not worth the hassle.

Was it the head gasket or the water jacket that failed?

Crank.. well if you kept going with no water and really over-heated it then the crank/bearings could well be in trouble.

Ken Simmonds: Part of the reason I got my T25 so cheap was that apart from needing a real dose of TLC it was suspected of having a blown head gasket. It lost its water to the point where it overheated and needed topping up several times on anything but a local trip. After replacing the heads with two reconditioned heads that came with the van the problem persisted. The tell tale sign was supposed to be bubbles coming to the header tank. However I determined that this was due to the somewhat Spaghetti Junction self-bleeding water plumbing so looked elswhere for the problem. I coupled my compressor to the system and at 1 Bar, 14.7 lbs/sq in or plus one atmosphere I detected a slow weep at the pressure cap. This blue plastic part was obtained for about a fiver from GSF.

I have kept the old heads which although having the permissable crack between the valves, were probably OK. And while not claiming to be a VW expert, but surely the heads could be lightly skimmed if the circular recess for the liner was also machined by the same amount*. By the way I was able to replace the thin "O" ring at the base of the cylinder without uncovering the rings (which could be a problem to get back in with the engine in the vehicle) by putting each piston to TDC while I did it. The "O" rings stretching over the barrel.