Head Gasket Going?

[PW@Woodsport]

Certainly pointing towards a HG failure.

[JamesDaniel80]

bu88er. Any tips on how to do a decent DIY fix without breaking the bank? Or the car?

If there is a decent online guide that would be good!

[PW@Woodsport]

Like i've said numerous times, you need to find out 100% if it genuinely has failed or not, and that can only be done with a pressure test.

After that the head needs to come off, inspect the block for corrosion, if it is corroded then the engine needs a full strip down, block decking and rebuild to fix professionally.

Some have stuck some chemical metal into the block pitting and sanded it flat to save them having to strip the engine, but it's a bodge and won't last.

[scomr2]

Paul what about a sniff test, is that not conclusive?

[JamesDaniel80]

I think I'll chuck it at a garage and get them to diagnose it properly rather than me messing about with it and potentially making it worse.

I certainly can't smell any oil in the coolant but it has gone a nice shade of brown even though I replaced it with brand new mixture and flushed it out completely only about 300 miles ago.

[PW@Woodsport]

Paul what about a sniff test, is that not conclusive?

No i've had a Mk1 pass a sniff test but fail my pressure test.

My reasoning for this is that the hydrocarbons that the sniff test need to see aren't being pumped into the coolant until the engine is under load.... which isn't happening at idle with the pressure cap off, such can be the nature of such a fine break in the HG they sometimes see.

I've tried all of the various tests on literally hundreds of Mr2s over the years and my pressure test is the only method that guarantees a HG diagnosis.

[pk_090]

Giving any ideas to what your method is Paul? I know trade secrets and all that, but my engine is behaving funnily at them moment so much so im tempted to sell it as spares/repairs to add to the s14 fund.
Its slightly harder to start, drives fine but then after a drive and it comes to idle it drops to 3 cylinders and smokes its bag off. Sounds similar to the OP's problem.
Alex

[kaiowas]

Giving any ideas to what your method is Paul? I know trade secrets and all that, but my engine is behaving funnily at them moment so much so im tempted to sell it as spares/repairs to add to the s14 fund.
Its slightly harder to start, drives fine but then after a drive and it comes to idle it drops to 3 cylinders and smokes its bag off. Sounds similar to the OP's problem.
Alex

It's no secret. Paul has posted it several times in the past. The common failure mode for a HG failure on a 4AG is a breach between the water jacket and the #4 combustion chamber (usually caused by corrosion of the block.)

To diagnose this Paul simply applies compressed air to each cylinder in turn (by replacing the spark plug with a suitable fitting) whilst watching for bubbles appearing at the coolant filler neck. If you get bubbles in the coolant whilst the cylinder is pressurised you know that cylinder has a pathway through to the coolant. The fitting Paul uses is, ISTR, basically the hollow threaded portion of an old spark plug welded to a standard airline fitting.

[PW@Woodsport]

That's it in a nutshell, plus it's not really my method, more commonly known as a leakdown test, but I just combine it with a simple visual test for bubbles in the coolant and a very basic tool for applying pressure to a cylinder on TDC.

Even if the bubble stream is a very fine mist, it totally proves HG failure, as before this extremely fine breach cannot be picked up by compression, chemical or sniff tests all of the time.

[ian08]

I did a sniff test on my Mk1 and it didn't show head gasket failure even though the HG had gone....
The amount of steam your car is kicking out, plus the other symptoms you're experiencing look like HG failure....

[PW@Woodsport]

Indeed, it's far from conclusive.

In order of test reliability/degree of HG failure...

1. Pressure test/visual bubble test
2. Sniff test/hydrocarbons present at filler point
3. Chemical tests
4. Compression test

The first one will detect even the finest breach, the last one requires the HG to have a full on failure that is enough to lower cylinder compressions (mk1s rarely fail in this way)

Just in my experience working on Mk1s for 17 years.

[pk_090]

Purely out of curiosity again, what kind of air pressure do you apply Paul?
Alex

[PW@Woodsport]

50psi, any more than that and it tries to turn the engine over, so keeping it out of gear and the handbrake on are musts!

Not that i've ever run myself over doing this test with too much pressure you understand

[pk_090]

That gave me a little giggle lol

[PW@Woodsport]

I had been rocking the car back and forth in reverse gear to get it on TDC for one of the cylinders i was testing, the office phone rang so i took the call, came back to the car and forgot it was still in gear, then immediately applied 150psi to the cylinder and of course it then ran me over.

I deserved that one

[SuperRedMR2]

LOL i'm so sorry I couldn't help but laugh at that one!