924Board.org

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

So, I purchased a non-running 924. I was assured that the thing was a good runner, just needed a battery and an oil change. Figured that was BS, and it needed a hell of a lot more than that, but bought it anyway.

Discovered that two of the large freeze plugs had blown out. Plugs totally gone, not just rusted through, and the lower hose form the radiator was frozen solid. So, it appears that the PO didn't bother to put any coolant in the engine when he put it in storage 13 yrs ago.

So I bought the plugs and filled it with coolant, and there's now a leak under the intake manifold. Haynes has no photos of this side of the block, but the only possible culprit for a leak That i can see is the head gasket. (There's 2 leaks actually, between cyls 2 and 3 and between 1 and 2.)

Questions:

1. Ever seen a frozen engine blow the head gasket out? Seems very fishy to me. My guess is the gasket blew, so the PO put it in storage, figuring that he'd fix it someday. Then he sold it to me and asserted the engine had no problems.

2. If my goal is to do only the head gasket, what are the odds that the head is OK? This is the first aluminum head engine that I'll be tearing apart. If it was a cast iron head, I'd feel reasonably comfortable about slapping a new gasket on it and running it as is.

3. Car is a 1977, as best I can tell, not a 77.5. It's the 95HP engine code, but it has front and rear swaybars. The difference in the low-HP and the high-HP engines is (basically) the valve size, correct? The 77 engines are also lower-compression. So, if I have the head off anyway, is it worth it to chase down a later model head with larger valves and smaller combustion chambers? Better idea to modify the existing head for the larger valves and deck the head?

My goal with the car is to get it running and give it to my girlfriend to use as a summertime daily driver. (I'm also looking forward to driving it my self.) I'd prefer to just get the thing running and get it on the road, but if
it makes sense while I have the motor apart, I'd like to 'correct' the 95 HP issue.

Thanks,
Brendan

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

There is a metal coolant pipe under the manifold, far more likely to be the culprit than the head gasket.

Image © Smooth Dog Toofahpics

Depending on your ambition level, it might be worthwhile to pull the motor to reseal it (oil, water and intake) and to inspect the clutch.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

Thanks, Rasta. I was hoping the pipe was the culprit, but it's running down the block from above the pipe.

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

The intake manifold has no coolant running through it on this engine, right?

Or does it? What is the channel in the head below cyl 2,3,4 on picture 19.17 in Chapter 2 in the haynes? Is that a coolant passage?

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

Here's the intake gasket.

http://www.autopartswarehouse.com/details/QQPorscheQQ924QQFelproQQIntake_Manifold_GasketQQ19771982QQFPMS22803.html

Maybe this gasket is the source of the leak? Can someone confirm that the square holes in the gasket are coolant passages?

Thanks,
Brendan

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

There is no coolant in the manifold. The extra pipe you see there is a vacuum line for the turbo.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

Dammit. Must be the head gasket then.

CorsePerVita · Joined: 25 Jul 2008 Posts: 1992 Location: Redmond, Oregon

Blown head gaskets are sooooo kewl.

_________________
- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

ugh. Did not need that photo dude.

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

TJC · Posted: Mon Mar 21, 2011 10:18 am Post subject:

Before tearing into it you can perform a Cylinder Leak Down test to help with your diagnosis, as well as testing to see if there are combustion gases in your cooling system.

Also, there are no such things as "Freeze Plugs". That is a HUGE misnomer. There are however "Core Plugs" and if one understands how the blocks are cast, one will understand why there are holes in the block that must be machined and then plugged with said "Core Plugs". If the core plugs in this engine have been "blown out" as you describe, there exists a possibility that the block may be cracked due to the expanding water (ice) that formed within it to cause the core plugs to "blow out" in the first place.
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
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Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

Thanks, but lets not revisit this nomenclature issue here.

The coolant leak can only be a cracked head, cracked block or a bad head gasket. The leakdown test is a good idea, but if I already have a bad head gasket, it's not going to reveal anything that could not be diagnosed as a bad head gasket, right?

The engine is not running now, so there won't be any gases in the cooling system. I need to figure out an unrelated electrical issue first before I can get it running.

TJC · Posted: Mon Mar 21, 2011 12:33 pm Post subject:

Given the nature of your situation and having no history of the engine I would not rule out any scenario. The leak down test can show the signs of a bad head gasket, especially if you are looking and listening for all of the places that it may be leaking from. However, if there was enough pressure created during the course of time to have the core plugs "blow out" then there exists a possibility that the cylinder walls were compromised as well and one (or more) could be cracked. This is a possibility that shouldn't be overlooked, and is difficult to detect. I'm guessing that you have already looked for the signs of water in the oil, and vice-versa.

I'd just hate for you to think that this problem of leaking coolant may be resolved by replacing the head gasket, and then find out that there is a problem in the bottom end.

Also, you stated that you replaced the core plugs and added coolant and then discovered the leaks. Were these static leaks, by which I mean did these leaks occur shortly after you added coolant? You mention that the engine is not currently running due to an electrical glitch, so am I correct in assuming that you have not had the engine running since you replaced the core plugs and added coolant?
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

Brendan · Joined: 04 Jan 2011 Posts: 63 Location: Maine USA

The engine cranks freely, and seems to have compression, based solely on resistance when turning the crank with a breaker bar.

When I changed the oil before cranking it for the first time, i witnessed no coolant in the flow of the oil to the drain pan (for what that's worth), but i didn't capture the oil in a clean drain pan so I could examine it later. There was no telltale gray sludge in the oil, as I have seen with other engines I've owned where the head gasket leaks to the cylinder or the oil system. This doesn't rule out a head gasket issue, however. It could be leaking outward, not inward. It's unlikely, but not inconceivable, that the head gasket is breached at the coolant passage, but not at the cylinder or at a passage (if one exists on this OHC engine) back into the oil pan.

I discovered the freeze plug issue when I saw the coolant reservoir was empty and tried to top it off before cranking it the first time. This morning, I replaced the plugs, and proceeded to fill the cooling system. As I waited to see the coolant reach the breather plug on the uppermost coolant hose, the coolant started leaking out from the head gasket.

Brendan

TJC · Posted: Mon Mar 21, 2011 2:07 pm Post subject:

Before taking the head off I would still perform a CLT to give yourself a better idea of the location of the leak and any other potential problems.

Since this car was parked for some time and did not have coolant in it there are other things to take into consideration as "did it have a chronic overheating problem" and "is there a chance that there are problems with other parts of the cooling system" ?

Does the head look to have been off of the block at some point or does it look like it has been on there since day one? The reason I ask this question is I have had engines (supposedly rebuilt or have had recent headwork) brought to me that were not properly assembled or had the heads torqued improperly. You may want to pull the cam cover to see if there is any evidence of this. Normally when a head gasket "blows" it will happen between cylinders and not externally, so your external leak seems to indicate something else is causing the problem. However, if the gasket did blow and the engine was severely overheated, then I could see a possibility of an external leak which could be caused by the gasket, warped or cracked head or cracked block...although in most cases you would also see water in the oil or vice-versa.

In any event it looks as though you will be pulling the head, but before you do check to see if all of the timing marks are correct when the engine is at TDC. If they are not, this will also give you a possible clue as to what transpired before the engine expired.

Also in regards to your question regarding what to look for with the aluminum head since you stated you have not yet had experience with aluminum head/cast iron block engines...well your're dealing with two dissimilar metals, and without using a proper coolant, and after sitting a long time, you are probably going to witness a fair amount of corrosion and pitting in the aluminum. Also if the engine was severely overheated, the head may be very warped or cracked., perhaps beyond repair.

Good news is that if that's the case, you can probably find someone here to help you out with selling you a head.
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com