Luminous

iTrader: (3)

Hiya

To cut a long story short, my gf has an aging VW Polo. The head gasket went a few months back and was replaced by a trustworthy local mechinc (VW specialist).

Roll on to present day and the car was misfiring badly. On closer inspection the top of the engine block was full of black (not white) crud, along with the air filter and breather pipe being totally blocked up.

On questioning the original mechanic he said he did not flush the engine during the head gasket change as this is no longer the recommended way to perform the work. Rather it was gravity drained and then simply refilled with oil.

I've had some advice from people regarding the car, and as always with these things there is not a total consensus of opinion.

Anyone else heard of engines not being flushed when head gaskets are done?

LC Geezer

If an engine has baked on oil depoists all over the internals, flushing ususally leads to a disaster. Flakes of baked oil get dislodged and clog up oilways leading to oil starvation of one or more bearings.

Luminous

iTrader: (3)

Hmmm, dammed if you do, and dammed if you dont

As not flushing it means that there was gunk left in the engine that caused the current problem. Ah well, at least I understand why they did not do that before.

ALi-B

iTrader: (1)

Not sure how old the Polo is, but old small engined VAGs have a habit of clogging up the top end and crankcase ventilation system with gunk, regardless of head gasket condition. Its usually caused when the car has been used for lots of short journeys (less than 30mins).

Flushing doesn't really cure this, as only oil/water vapour (the ingredients of sludge) only builds up in the areas of least oil flow and are coolest, allowing it to condense and form sludge. Engine oil flush only really flushes areas of high oil flow, which is basically the oil galleries, pump and sump.

The best way to properly remove sludge build up (or from a previous HG failure) is a full engine strip down and chemical clean or 3month oil changes (with a basic oil with good detergents) for the following 12month and regular hard blasts up and down the motorway (cough, sorry, autobahn ). Usually this is far too much hassle for the average person, so its left; the onus being the crud is only built up in areas where it doesn't cause a problem, so can be left and not cause any harm.

The exception being the crankcase ventilation system, such as the PCV valve and pipework, which can cause problems if blocked. So should be removed and manually cleaned with solvents (or replaced).

However, there is one thing I need to point out which raises an eyebrow; The headgasket. When this was replaced, what work was done to the cylinder head?? To do the job properly, the head should be crack/pressure tested and checked for warping. During this process the head is usually de-coked, cleaned and skimmed. More often than not this type of work is sent out to be done by a engine builder/cylinder head specialist, which then comes back to the garage looking like new all ready to bolt on. When you mention the head is full of crud, it seems to tell me that this wasn't done and the head wasn't checked for any damage from overheating or etching/corrosion (from old coolant thats gone acidic)- which is usually the cause of the gasket failure in the first place.

The consequences of such, is its quite possible for the gasket to blow again if the faces aren't properly cleaned or the head is slightly warped. Remember it may not lose coolant or mix water/oil, sometimes they blow between two cylinders, causing a missfire (lost compression on the two affected cylinders).

The fact you may have a misfire now maybe just incidental so I don't want you barking up the wrong tree. However a blocked PCV system isn't going to help.

Luminous

iTrader: (3)

Cheers for that Ali

The car in question is a T-reg Polo. Its done about 115k miles. Some would say its time to move it on, but cash is really tight atm. Clearly throwing good money after bad is not good either, but there is just not enough cash to change cars atm.

What is a PCV? Is that the oil pipe breather off the back of the engine into the air filter? I know that is solidly blocked. I don't think the head gasket has gone again as there is nothing in oil/water to suggest so, and the misfire was cured with new plugs and leads.

Crossing fingers that a new breather pipe, filters and oil may get some more life out of the little thing

(P.S. thanks for moving into other marques....I should have known better )

ALi-B

iTrader: (1)

PCV valve: Positive crankcase ventilation valve.

Basically just a one way valve in the breather system.

I think its located on the rear of the crankcase (where you can't reach it) on these. Its a case of following the breather pipe work. Removeing/inspecting/cleaning as you go along.

You'll probably find it will carry on for ages like that. The only big issue is if it start pushing oil out the breather and clogs up the airfilter. Usually what people do when that happens is remove the breather pipe and let it vent to the atmosphere (which then helps rust proof the chassis underneath when it gets really bad ).


(ps. I didn't move it; Some other busybody beat me to it )

Luminous

iTrader: (3)

Oh it pushed oil out of the breather and into the air filter alright. Never seen so much gunk in a filter before (I'm no mechanic). Had to toss the air filter to get the car running to get home.

Avi

My 1.4 16v mk4 golf is a killer for this.. loads of sludge builds up out of the crankcase breather in the air filter. My bro only uses it to drive to work and back (2 miles) so loads of short journeys. I just clean it out every few months. Everyone keeps saying the headgasket is going.. but it's been fine so far. Seems a common problem.

Luminous

iTrader: (3)

Cool, sounds like good news to me The car has done a fair few short runs, and the longer ones have often been in traffic.

Looks like there is hope for the old girl yet

Leslie

It might necessary to flush the engine if it tends to clog up as was stated. A head gasket replacement should not require that treatment, the bloke is not likely to have filled the sump with scrapings off the block it he knows what he is doing. He wouild have to actively try to get stuff in the sump anyway.

I have done that job many times and never found it was needed to flush afterwards.

Les

Luminous

iTrader: (3)

Cool, nice to hear some differing opinions. The three mechanics I talked to looked at me as if I had two heads when I said it had not been flushed

So many different ways of looking at things.