Jon Shutz

For months now I've had a problem venting my coolant system and I'm about to give up and let it have it's way.
Here is what I do when I vent the system:
I can seemingly get all the air out if I put the front of the car on jacks (wheels about 6-8 inches off the ground) and if the car hasn't been run that day...first thing in the morning seems to work. I take the expansion tank cap off, squeeze the upper radiator hose a bunch of times, and open the bleed screw till all the air escapes and coolant comes out. Then I start the engine with the car still on the jacks and turn the heat on full blast. I'll then rev the engine at 2 grand for about 30 seconds (making sure not to heat up the engine).
Then I shut off the car, go back to the bleeder screw and let the air vent out (with the expansion tank cap still on). I re-tighten the bleeder screw, then start squeezing the hose again and repeat the whole process 4-5 times before I get almost no more air to come out.

So here is my real problem…
I notice the famous “lifter ticking sound (clack, clack, clack)” and the “pouring” sound of water entering the heater core when there is air in the head because the clacking and pouring sound disappear after I vent the system. The clacking and pouring sounds will not return and the air will stay out of the head as long as I keep the heat turn all the way hot so the heater core stays “active” or “full” (the fan speed seems irrelevant.). I also notice the coolant level stays pretty close to the same no matter how long I drive as long as I keep the heat on high.
However, I live in Santa Fe, NM and can hardly bear to keep the heat on high on a 95-degree day. When I turn it to cold or put on the AC for more than a minute or two, the “pouring” and “Lifter ticking sound (clack, clack, clack)” comes back and air returns to my system (more air at bleeder screw)…coolant level rises and sometimes even overflows if I’ve filled the system to the max level.
I tried to find a new expansion tank cap locally but since the closet cap is an hour away,
I tried bending the tabs on the radiator cap inward to create more tension on the spring (incase it’s weak) but it still provides no help. I don’t think it’s the cap.
I seriously doubt it’s a blown head gasket because like I said, the air stays out if I keep it on hot or the heater core is in use. I also have checked each and every cylinder for coolant and have found none. The system does remain pressurized overnight so I don’t think I have a leak in the system. Could this be a heater valve? How can air get into a pressurized, vented system otherwise?

A correct answer would be god-sent at this point!
This car has been great to me other than the coolant system (ironic considering H20 isn’t Porsche’s roots) and it would be perfect if I can work through this
Thanks in advance!

Regards,
Jon Shutz (wishing Porsche stuck with air-cooled engines at this point!)
88’944, 69 Bug, 69 Karmann Ghia

Skip

Aargh, I don't have the manual with me, but I think your engine still has the rear bleeder screw (exhaust side of block just below, near piston #4).

So, two ideas:

1. you should be allowing the car to run with the heater on for a while longer... the point is to get the heated water circulating AND open the thermostat. Therein lies a possible problem... your thermostat is not opening? Could it be.. do you have abnormally high engine coolant temps (understanding you live in a not-so-cool-climate)?

2. Are you milking it? Gotta really milk those hoses sometimes to get all the air out.

I'd say start with a bleed, then run the car for ~20 minutes (heater on), then bleed again, then run again (heater on). If that doesn't do it then you may try the rear bleed screw (read: hard-as-hell-to-get-to-screw). They stopped putting these in the blocks in 89 (which had me scratching my head for ~30 minutes trying to find one on mine )

Good Luck... it's very unlikely you're sucking air into the system without losing some from the same location... maybe looking for a leak?

Also, here's a link to the Tech-Session article I did on coolant bleeding:
944 Coolant Bleeding

Jon Shutz

Thanks for the reply Skip!

To answer your questions:
“1. you should be allowing the car to run with the heater on for a while longer... the point is to get the heated water circulating AND open the thermostat. Therein lies a possible problem... your thermostat is not opening? Could it be.. do you have abnormally high engine coolant temps (understanding you live in a not-so-cool-climate)? “

I do let the car run for 15 minutes on the last 2 bleed cycles I perform(I failed to mention this).
The car runs amazingly cool considering the climate I live in. the car usually runs at or just above the first white line but will approach but never reach the 2nd line when the AC is turned on and air starts entering the heater core.(I'm using water-wetter)
The lower hose off the water pump gets hot and the radiator fans come on so I’m pretty sure the thermostat is good.

2. Are you milking it? Gotta really milk those hoses sometimes to get all the air out.

Yep...milking it till my forearms hurt.

"but I think your engine still has the rear bleeder screw (exhaust side of block just below, near piston #4)."

After almost one hour of looking all around # 4 I still can't find this other bleeder screw. I'm thinking 87 was the last year since the 88 is a slightly different engine. However, if I’m mistaken and there is a rear bleeder screw, can you be more descript in where to find it? What part is it located near?
I also do not notice any coolant leaks and I have no coolant loss unless it’s come out of the overflow tube.
I’ll give it one more through bleed and make sure I let it run for a really long time this time. I’ll post with my results

Thanks again Skip!

Skip

Hmmm, sounds like you've covered all bases. What's the rad cap (expansion tank cap) look like? Good seal? No milk-shake?

Here's the scan from the manual that shows the location of the block drain plug. (says the block drain plug was discontinued on 89 and later models... mine's an 89)



Good Luck!

IceShark

You don't have to run that heater fan to keep the coolant running through the heater core. That should help a bit in keeping the cockpit temps down. Also, if by not running the fan this problem does not seem to differ then it must not be related to the heater core helping the rad by extracting additional coolant heat. Which is confirmed by your general system cool temp running comments.

So it has to do with flow by shutting the heater valve. You could start by replacing that short (4" or so) piece of hose between the heater valve and hard line with clear plastic from the local hardware store. Then you can see what happens there.

I know engine designers hate to have any coolant lines run off the engine for other purposes like heaters but they long ago gave up on objecting and faced the real world. Funny flow issues sometimes pop up. And I have heard of coolant system leaks that go one way - coolant will not escape but air can be sucked in. Seems sort of strange but I guess I could see it happen in the heater valve in that the water is shut off but the valve leaks in air on the exit side when shut off. But the valve is tight to both air and water when open.

I'm just thinking on my feet here. If you stick in a piece of clear test tube take off the valve and see if you can suck air into it from the side that goes to the heater core when it is in the closed position. And you should add a short piece of clear test tubing on the exit side of the valve, too.

I don't know how that head flows but I would definately track down a diagram. There could be a blockage. If the heater is open there is enough flow so everything is OK. Shut the valve and there is not enough flow so hot spots develop steam the coolant and there is your "air".

Skip

Yes, some cars are prone to sucking air without leaking... some that I've heard/seen: Mid-80's Freightliner Turbo-Diesel, Early Mazda rotax, some late Toyota F1 cars... most have one thing in common: the pressure created from the circulation of the cooling system (e.g. big mamo-jammin' pumps)is greater than the pressure created from the expanding coolant mix. This means the engine would suck air in at very high rpm's. The big result of this is expoding radiators and coolant tanks. The pressure is so high that the built-in safety relief would not react quickly enough. This is rare, but does happen. That said, I doubt the 944 engine would normally be able to reproduce these results.... though a good point to check the heater valve. Usually in failure mode it just leaks fluid (all over the clutch plate)

"Iceshark" - What year/model car do you have?

Skip

IceShark

Skip, an '88 951S.

Say, read my Distributorless Conversion thread and see if you have any leads/ideas for me.