Steen Jensen

This might help. Situation is quite similiar. Turned out to be a cracked cylinder head...




My mighty 456 has had some big problems. End of last year, after about 10,000K's of faultless operation (total about 50,000K's) the temperature started to skyrocket. Initially the mechanic tried a new radiator cap, saying he'd had a few that were losing pressure that way and it might be a quick fix. Once started up again and warm, the system pressurised and the radiator literally split - dumping all the coolant and leaving far too big a problem for a quick fix. An aussie firm, PWR were absolute legends - a new, beautiful aluminium radiator and pair of better performing fans were provided and fitted up just fine. All super until about 3 hours later when the head gasket appeared to blow out and we were flooded in coolant again.

This is where it all gets scary of course - engine apart, new gaskets etc etc - and after a painful wait and a healthy chunk of change it went back together aaannnd - once warm, went to hot, then very hot - then water was leaking from the engine again. Engine apart and there's water through it, so it appears bad (note I'm relating what the mechanic has told me).

The mechanic has always done the right thing by us, so I know he's trying hard. He's checked the fans, thermostat, piping etc etc - and says they are all good. He's looked in the bores and thinks they're ok. That leaves the head, which he believes has an internal crack that is widening under heat, and causing the problems. It's gone off to a specialist - however it's a catch 22. If the head tests 'good' then WTF else could be wrong? If not, then were the funk do I start looking for a new 456 head!?

Any ideas muchly appreciated.

timp928

Thanks Steen - not what I wanted to hear - but it adds weight to the theory that a blown head gasket may in fact be capable of blowing the radiator.

Update:

**As the radiator is out these tests were performed with the engine cold - so less than optimal results were expected.**

We removed the spark plugs and the fuel pump relay to perform a compression test today, interestingly the Workshop Manual says that the compression should be 8 bar and more (when installed ) and sets the wear limit at 6.5 bar - the section was referring to the 1988 model, I assume it is similar if not the same for my 1990?

The Spark plugs have done about 40,000kms and looked fine (see Pic).

It took about 4 "turns of the starter motor" to hit maximum pressure, the right hand bank started at 75 psi , and the left hand bank started at 125 psi. The Final compressions read (in PSI) were:
1: 100, 2: 200, 3: 190, 4: 190
5: 210, 6: 210, 7: 185, 8: 210

With 1 bar = 14.5 PSI, 100 = 6.8 bar - still above the wear limit; and 210 is way up there at 14.5 bar - does this seem too high?

Remember this car was driving - albeit casually - without showing any symptoms of being down on power, or running rough - just coolant flowing freely out of the radiator ...

We then performed a leak down on Cylinder1, and even though we had it at TDC, it would not hold pressure. Airflow was detected at the exhaust and was audible in the engine bay. (We also tested the leakdown tester on cylinder 2 to ensure we were operating the tester correctly, and it the cylinder held pressure as expected (see Pic))

We then reconnected the leakdown tester to Cylinder 1 and turned the engine over (by hand) to see if we could find a point where it held pressure - we couldn't.

Looks like the head needs to come off for further inspection(?) - perhaps a leaking valve, or perhaps small leak in the head gasket that is only evident on the compression stroke?

I have yet to collect oil/ coolant for the samples and get the radiator cap tested, but it doesn't look good at present.

regards
TheTimp
90 S4
Black on Black

Lizard928

From your compression test numbers there is problems with cyl 1.
It is less important what the numbers are but the consistance between them.

Though the 185 compaired to the 210 is fine because of heat expansion and cam timing change once the engine is hot. However, with you doing a leakdown test and what you state. You either have burnt or bent valves in cylinder 1. This still will NOT cause the rad to pop like it has. And the hissing in the engine bay is from air passing the rings. This is normal to hear on all cylinders! As the ring do not seal 100% and even less when engine is cold.

S4ordie

I agree that leaking rings or burned valves will cause compression leak down. Also agree this does not cause pressure in coolin gsystem.

I recommend getting the car to a place where you can hook up a gas analyzer to the exhaust. That can tell you much.

timp928

I got the coolant analysis back and they say:

All metals (Al, Fe, Cu & Pb) are within normal limits. Contamination elements (Ca, Mg) appear normal. The corrosion inhibitor level (Nitrite) is normal. pH level is normal. Glycol level is to low to provide adequate boil and antifreeze protection.

Not sure why the Glycol level is to low, but all that coolant is gone now, the block has been drained.

The good news is there was no evidence of combustion gases in the coolant - so the head gasket should be ok.

The bad news is that it looks like the radiator has failed for reasons unable to prove. I am getting a new one made, and including a connection for a pressure sensor, so I can monitor it.

Unfortunately I cant put the car back together with a "known issue" - leaking value - so I am going to pull the heads and correct it at the same time.

Looking for any advice on head removal, and parts to routinely replace.
Wont be pulling the motor, as I don't have the height in the garage to do it.

regards
TheTimp
90 S4
Black on Black

Imo000

Well......when I was filling up my '85 with a coolant mix, some leaked out at the bottom of the rad. This was all new to me, as it never leaking anyting like this before. .........This was 2 weekends ago and as soon as the engine warmed up, the leak dissapeared. I know that NOTHING heals itself, so this leak wil come again, probably really soon,............In the mean time, the end tank probably has a leak of some sort.

Mrmerlin

NAPA has a block tester, to test for hydrocarbons in the coolant, not sure if you have a NAPA though its about 50.00 for the kit, you suck the coolant fumes through a tube filled with blue fluid and if it turns green or yellow you have a hydrocarbon source leaking into the coolant.
I would be interested to find out more, also replace the coolant bottle cap with a correct porsche part

tveltman

It seems like you just have a fried/bent exhaust valve. If all the spark plugs were out, and there was a leak in the head gasket or a crack in the head/block, I'm pretty certain that you would hear the air howling out of the adjacent cylinder, or you would see bubbles in the coolant tank (in your case you might just hear the hissing if there is no coolant in the engine), or you would hear it hissing loudly out of the dipstick. If you didn't hear any of those noises, nor did you hear air howling out of the MAF, but did hear it out of the exhaust pipe, then your engine problem is probably limited to the exhaust valve. If, however, your valve is stuck open AND you have a crack in the head that joins the exhaust valve to the water jacket, you can end up with superheated coolant as the 1000+ degree exhaust diffuses into the circulating coolant. I believe that aluminum begins to deform around 250 C (480F), and so if the coolant got hot enough, it could generate super-normal pressure AND potentially cause damage to the radiator. The only problem with this theory is that the temperature gauge seemed to be operating correctly. Did you verify that it is functioning correctly and that the gauge on the dash reads what the sender suggests it should? That's all I have to say about that, good luck!

69gaugeman

An all aluminum that can't take 14psi? I call bull**** or REALLY crappy rad. Ballooning? with 14psi? Again only if they used aluminum foil for end tanks.

Unless someone can show other wise I find it hard to believe a rad of reasonable manufacture would be the weak link.

Mrmerlin

Yes I agree, the cap should have vented first , not let the rad balloon

WallyP

I haven't seen any report of a test on the radiator cap. That test really needs to be done. It should start venting pressure at 1 bar (approx 15 psig). If it doesn't vent, that would blow something - I would have expected it to be a hose, though.

I would also crank the engine and retest the compression before I pulled the head - it is not impossible for an exhaust valve to be hung open, or to have a piece of carbon lodged under it.

It is a good practice to loosen the spark plugs and then crank the engine prior to making a compression or leak down test. It is not uncommon for there to be deposits around the plugs that are broken loose when you remove the plugs. There is enough flow to carry the deposits to the exhaust valve, and it is not unknown for a piece of the deposits to lodge between the valve and seat, causing a leak. Running the engine after loosening the plugs usually takes care of that problem.

Jfrahm

Yes I concur on rechecking the compression and leakdown, hopefully after a heat cycle and the test run on a warm engine.

timp928

Pulled the heads off at the weekend - now that's a fun job!

I wish someone had told me a need to go on a weights course for a month to undo the Head bolts!!!!

The heads and block look ok (dirty etc as expected), I cant see any major issues.

Dropping the heads into a head guy today, to get a professional opinion.

Of course I took a few photos...


http://www.flickr.com/photos/2318054...7622113258378/

Have a peruse if you are interested in what the internals of a 460,000kms engine look like.

Once the heads are off there is plenty of room in the engine bay to do other things...... oh dear :-)


regards,

Timp
90 S4
Black on Black
Queensland
Australia

Mrmerlin

to clean the block mating surface get a box of one sided razor blades, then holding the blade perpendicular to the surface go back and forth, this will take off the top of the surface without digging in and gouging the block, use lots of blades.

_>____I___<__ I= the blade _________ = block surface <> = back and forth

timp928

Thanks - any tips for the tops of the pistons?

regards,

Timp
90 S4
Black on Black
Queensland
Australia