LazerSquid

Alright, so I recently purchased a 1984 porsche 928 s, that was in poor condition and I would have to drive it home (only about 4 miles). The seller stated that the only problem the car had mechanically was that the transmission was slipping, which I though wasn't a bad tradeoff for finally owning my dream car. So I get the keys to my new baby, do my pre-first trip checks, fuel, oil (a little low), and coolant, and I set off. I immediately noticed the slipping transmission and that it wouldn't shift out of 1st; "alright, this isn't so bad, I was expecting this" I thought to myself, and was having a good time until about 5 minutes in to my trip ( 4 miles but very low speed limits), when the temp gauge didn't stop where I was expecting it to, and kept climbing and climbing until it pegged red. I immediately pulled over and popped the hood, and watched about 2 gallons of coolant spray from the tank. At this point there was no turning back, and I had no means of towing it, so I had to just limp it home. It kept pegging, and I kept stopping and waiting for it to go back down to the first mark and refillin the coolant and by the time I got home it had pegged the redline about 5 times. It didn't seem to have any problems the next day though, it started right up, idled perfectly, and didn't skip a beat, and I thought I had dodged a bullet.

That's the back story. The next day I discovered the PO removed the thermostat, so I replaced it, and let it cycle through, and to my pleasure it idled for about 30 minutes with the temp gauge directly where it needed to be. Then I decided to top up the oil, so I bought two quarts of oil and poured one and a half of them in, til it read completely full on the dipstick. However, this time when I started it, there was heavy white smoke in the exhaust, that lasted for about 5 minutes and then dissapated. It still ran fine though, so I let it sit for the rest of the day and researched what it could be and read that it was overflowing through the intake and the engine was burning off the excess oil. The next day I got it out and drove it a bit and the temp gauge stayed where it normally would, so I decided it would be okay to drive just a little bit further, however, about two miles away from home it started climbing rather rapidly, and before I could find a place to stop it had pegged again. I waited for it to stop boiling out of the resevoir, filled it up, waited for it to cool down, and drove very slowly home without it overheating again. In the morning when I started it, I was met with the same white smoke, however this time the car was running very rough, which it wasn't doing the day before, and I figured that it had fouled a plug, so I bought new plugs, oem-spec, and replaced all the old plugs. None of the plugs showed any signs of any poor operating conditions, they were all a perfect brown color like the car had been operating perfectly, none of the cylinders had coolant in them, but two of the spark plugs had oil on the threads when I removed them. With the new plugs it didn't smoke quite as long, and it ran rough at first but quickly started running very smoothly, so I took it out for a ride, and about 30 seconds in it started running rough again like it's missing on a cylinder or two.

So in short, the symptoms are;

white smoke at cold start
intermittently running rough
overheating


the only thing I really noticed was that the electric auxiliary fan never comes on, but I can't imagine that little thing would cause all of this trouble. I keep thinking that it's a blown head gasket but it doesn't seem to have all of the symptoms of that.

The Forgotten On

Do a complete ignition service, i.e new wires, distributor cap, rotor, and the green wire. That should help with the rough running. Do a coolant flush and get the correct G-05 coolant put in, that should help with the overheating but you might need to have the radiator professionally cleaned to remove anything blocking the coolant passages and in the worst scenario replace the radiator. You could have a leaky oil cooler in the rad which would allow water into the oil and cause white smoke or you could have a bad head gasket. Good luck

Mrmerlin

I am gonna guess you have a few problems first might be a cracked head,
and its letting coolant into the cylinder hence the smoke,
take a careful look at the plugs again,
any that might look a bit cleaner than the rest or have rust forming on the electrodes will point to water in the cylinder.

you should get a block tester from NAPA and test the coolant for hydrocarbons,
if that test comes back negative,

then replace the waterpump,
and the heater control valve, and short hose
the thermostat and the rear seal for the T stat.
the coolant bottle cap



The slipping trans may be low fluid,
dont keep driving the car till you have topped up the fluid,
as you could be ruining a good trans that needs a quart or two of fluid,
Use Dextron 6

Landseer

You have a lot of refresh work to do on that car.

Take the battery out before you try to start it again.

LazerSquid

Sorry, I forgot to specify that I had already fixed the transmission. On of the coolant lines (line #5 on the parts diagram) had come completely unscrewed and was spewing fluid out. Can't believe the PO didn't see it.

Why remove the battery before trying to start it again?

Landseer

Highly possible that water pump is shot.

Lizard928

First things first, pull the plugs and inspect.

LazerSquid

Already pulled the plugs, they lopked perfect

M. Requin

M. Requin

LazerSquid- If I were in your shoes I would do exactly what MrMerlin suggests. The coolant contamination test is simple, and you can likely borrow the tool. Exhaust hydrocarbons in the coolant, you have problem with the head, no contamination, go on to waterpump, etc. It's a pretty simple diagnostic path and should put you on the right course.

LazerSquid

I just remembered another symptom is the tachometer/speedometer works very intermittently, and usually comes on right as the car begins running rough, I don't know if that would have anything to do with it. I will test for hydrocarbons today.

LazerSquid

Just now took it for a very short drive to lobster be symptoms and she started running rough, but not quite as hot. Also, when I let it idle in park the temperature dropped down very quickly, so it only has issues overheating under load. Also, when I parked it was running rough, but I turned it off for maybe 5 or 6 seconds and started it again and all was back to normal.. If It didn't keep jumping between screwed up and perfect I wouldn't have as much of a problem deciding on heads or pump, but this is just very perplexing to me.

dr bob

Echoing the advice of the others:

-- Get all the ignition bits up to current if they aren't. Stoooopid stuff like a cracked distributor cap will get you the symptoms you describe. You were going to replace all that stuff anyway to baseline your maintenance program, right?

-- Clean All the Grounds. A little searching here will net you some valuable guidance on all the grounds.

-- Do Wally's annual electrical maintenence complete. That includes the grounds mentioned above. Look on the 928 Specialists website at www.928GT.com, and click through to Wally's World.

-- Do at least a visual check of the electrical connections and wiring in the engine bay.

-- Do the same check of vacuum hoses and related things under the hood.

-------------

Then refill the cooling system carefully, remembering that there are high spots in the water bridge, the top of the radiator, and the coolant reservoir. It takes a bit of fiddling sometimes to get the air pockets moved to the reservoir on coolant fill.

The thermostat is particular to the 928, in that it meters coolant recirculation flow through the block as much as it does flow through the radiator. It's way different from the systems you know from 'murican or Japanese cars. If you bought a parts-store thermostat, there's a good chance it's not the one you really want.

The thermostat housing in the water bridge has a rubber seal at the rear of the thermostat where the smaller disk seats. Those tire and harden with age, and need to be replaced with the thermostat. The old one will look and feel like metal, but does pry out to allow a new one to be fitted. Failure to replace this seal, or using the wrong thermostat will cause the majority of your coolant to bypass the radiator.

The PO hinted to you that the car has cooling problems by pulling the original thermostat.

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[rant mode]

There is no situation that includes "I had no way to tow it so I drove it until it overheated a few times, let it cool a little, then overheated it again and again with all the coolant boiled out, until I got home." The "no way to tow it" part is defective. Repeatedly overheating the engine, runnng it with coolant boiled out, is a recipe for disaster. It's an aluminum engine with aluminum pistons and tight clearances. The coatings on the pistons and the cylinder preparation are key to engine function. Scrub a bore, and the engine is a boat anchor, simple as that. Dream car turns into nightmare in a quick heart-beat.

[/rant mode]

Bill Ball

Initially I thought loose water pump impeller, but when you idled it for 30 minutes with no temp problem, that went off the list. Still, rapid overheating is consistent with a loose impeller. Hard to explain otherwise. Same with blocked radiator (quick overheat, still overheat on idle). The missing Tstat was an early contributor - you understand the Tstat is essential to cooling in a 928 unlike many American cars - but you fixed that, assuming you installed it correctly with the large o-ring on the correct (front) side) and you should have replaced the seat (hard to see once corroded over) that is pressed into the waterbridge. But even if not, the Tstat alone should work well enough. So, I don't have a unifying theory. But if you conclude the head/head gasket is still OK, I'd be doing the water pump and have a radiator cleanout done by a good radiator shop.

Any more WHITE smoke? White would not be oil.

You should never have allowed the temp to get to the redzone, even if you had to stop and let it cool off every 100 yards.

LazerSquid

I know that I should not have allowed it to redline, but my judgment was very clouded by the frustration of an unannounced problem, and I did the stupid thing to do and drove through it, but that's the past now and there's nothing to do about it. I am mechanically inclined and I do know better, and I'm kicking myself for what I did, so enough bashing my poor judgment


Dr. bob, all of those are very good suggestions and I will be doing all of the things you suggested when time permits.


Bill Ball, those are also good suggestions, and I knew the basics of how the tstat works in these cars, but your explanation make me pretty sure that I did in fact get the wrong part, so I'll be ordering the correct one as soon as possible.

Thank you everybody for your helpful comments!