[968Syncro]

Hi Cloud,

I am following the discussion since I have the same general feeling that my 968 ran cooler 3-4 years ago. Normal driving at speed, and 80 ambient the needle stays at the 8:00 line, or even below. But when I get into traffic around town, let's say 3 red lights in a row, short distance between them, the needle can creep up to close to 10:00, but never above.

Then I have noticed that usually in just 1/4 mile or 1/2 mile of 45 mph will bring temp down pretty quickly. But terrible feeling, until recently the needle would stay up there, and I started getting real concerned. Only thing I can offer is --- believe it or not -- tapping on the plastic in front of the gauge brings down the temperature immediately. [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img] True, in certain circumstances the needle will fall back down from near 10:00 to just above 8:00 when tapped. [On my old MGB I installed doorbell hammers on every gauge to help manage the Lucas equipment in the same way [img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img] [img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img] ]

One thing on my list, again, is to check the fans and all the wiring -- had a blown fan fuse last summer. I also think one of my fans is tight, it doesn't spin as freely as the other one, so perhaps it just isn't moving as much air as previously.

Roland

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[Cloud9...68]

Uh-oh... Not looking good so far. I performed John's test, and there's no coolant whatsoever flowing from the small hose in the back of the reservoir into the reservoir. Not a drop. Is this a sure sign the pump is bad? I really don't want to tear the front of my engine apart yet again unless I'm REALLY, REALLY sure it's the pump, as I went through this once already, only to find the pump was fine, but my car definitely failed John's test miserably.

I still don't understand why my engine, at least according to the temp gauge, isn't getting THAT hot (compared to what others are reporting), unless I drive it aggressively, and why the problem isn't getting progressively worse, if I have a dead (or dying) water pump. I guess I'm in denial.

I think I'll next remove the timing belt cover and check the tightness of the timing belt against the water pump pulley, though I think this is a long shot. After that, maybe I'll remove the thermostat. If it definitely turns out to be the pump, I think I'll continue driving it like an old lady until I remove the head for its upcoming pre-supercharger rebuild, hopefully this fall or winter. But of course if it starts getting near the 10:00 oclock line even in moderate driving, I'll tear into it sooner.

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[Cloud9...68]

Syncro,

My car's behavior is a little different than yours. Stop-and-go traffic in hot weather isn't that big of a problem - the gauge gets to about 9:00 oclock, which is higher than it did when it was healthy (I don't remember it ever getting above the 8:00 oclock line in traffic before these problems started), so I think your engine may not be getting enough air flow from the fans, as you suspect. My fans blow up a storm, and keep things reasonably under control in part-throttle conditions. It's only when I floor it and explore the rpm range henceforth to be known as "The DS968 Realm" (4000 - 7000 rpm) that things really start to cook. Easing off brings the temp back down, but pretty slowly. So, it appears that my problem is coolant flow, while yours seems to be air flow. Wanna trade? [img]style_emoticons/<#EMO_DIR#>/ohmy.gif[/img] [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img] [img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img]

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[DaveN]

Maybe if your pump isn't pumping there is a bit of an air pocket wandering around your thermostat as well and giving you odd readings

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[banditsc]

You may need to actually verify the plastic neck is the proper one on there. They are actuall two kinds of necks, a block off neck which doesn't ahve the hole drilled in it, and out kind which has a hole. It's apparently common for people to put on the wrong one and not check if ther eis a whole in the neck.

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[Cloud9...68]

Banditsc,

When you say "plastic neck," do you mean the little neck in the back of the overflow reservoir that the small hose coming from the top of the radiator goes into? If so, the only way I can see to check whether it is blocked off is by removing the hose, which isn't a huge deal, but mine is held in place by one of those moronic clamps that you have to basically destroy in order to remove. I don't object to doing that, and then replacing it with a normal screw-tight clamp, I just want to be sure I'm thinking of the right part before I mangle that clamp.

If the neck is blocked off, what does that mean? Do I need to drill a hole into it? What purpose does this return path to the reservoir tank serve, and what harm is there if mine is blocked off? I've never replaced the reservoir, and the car ran nice and cool once upon a time with it. Thanks.

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[banditsc]

The neck that is attached to the water pump. If it's ever been replaced there is a chance the wrong one was put on and doesn't have a hole in it. Not sure of the exact problem it would cause, but I'd guess it wouldn't cool as efficently since that water path is blocked off. If it's blocked all you need to do is drill a hole in it.

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[John]

Cloud...,

To follow up on the water pump id, the 968 p/n is different from that of the 944 Turbo and of the 944S2, though I couldn't tell you what the differences are. One is probably the blocked-neck mentioned by banditcs.

Re. the operating temps of the thermostat and the radiator fan switches, these should track. You can't change just one and not the other. Non-matched ones would effect efficiency, but it's hard to see how it would cause your cool lower hose.

Re. you question about actual temps, here's how mine behaves, engine fully warm, at idle (all temps in deg. F):
-- fans just off, temp in lower hose at 160, builds through to around 180
-- fans go on, temp in lower hose continues to build through around 195 then begins to drop as thermostat opens,
then fans go off again.

Another way to think about the lower hose being sometimes cool:
-- the thermostat faces the radiator, so the temp of the coolant in the bottom of the radiator and the hose is what
triggers it to open.
-- it can't not be hot! But it is ...

Re. your question: "What purpose does this return path to the reservoir tank serve, and what harm is there if mine is blocked off?" That's the constant circulation path I was talking about. Who ever changed your pump might not have noticed and just hooked up the hose. Have to think how this might effect things.

Though it probably will be of little help with your issue, you might take a look at "Electrical Trouble-Shooting the Porsche 969 Cooling System" pdf in the DIY Library, Electrical area.
... John

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[flash]

the thermostat actually faces the engine (the coil faces away from the radiator) - i still find it odd they placed it there though, rather than up top like most engines - seems to me it would always be fighting the flow - but, i suppose it does mean that the coolant temps are closer at each side of the thermostat, which is what you want, as opposed to wildly swinging temps

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[Cloud9...68]

"then flow needs to be verified - this will be a messy job, but very brief - pull the return hose, connect a length of hose from the fitting on the engine to a bucket, then fire it up and watch what happens - if the pump is turning, there will be a LOT of coolant exiting - if it isn't there will only be a little bit"

Even though John's technique indicated a lack of coolant flow, I'd like to do some more flow tests, seeing as I have nothing to lose, and I'd like to be as sure as possible it's the pump before pulling it. Reading Flash's method quoted above, I'm a little confused. When I replaced the pump a couple of years, ago, I spun it in what I was pretty sure was the correct direction, and found that it pushed the coolant back into the block. So, I assume the coolant flows through the block and head, and out the elbow on the front of the engine, into the radiator through the hose attached to the elbow. If this is correct (and I've never been able to verify it, so it may not be), wouldn't it make more sense to remove the top (inlet) hose where it connects into the top of the radiator, and check for flow of coolant? The fitting on the engine where the fat return hose connects leads to the thermostat, so unless I removed the thermostat, I don't see how there would be any coolant flow there. Again, this may well just be my ignorance on display here.

Also, do I actually need to fire up the engine to check for coolant flow, or could I just run the starter? I'm a little concerned of sucking air into the system if I fire it up, and my assistant doesn't turn it off in time. In fact, doesn't any check of the pump's ability to circulate coolant require removal of the thermostat?

A diagram showing the path of coolant flow through the engine would sure be helpful...

And to address Banditsc's comment about the neck that's attached to the water pump, the way I bleed the sytem is by attaching a hand pump to the reservoir's opening (where the cap goes). If the plastic neck attached to the front of the water pump were blocked off, the air from the pump wouldn't be able to pressurize the system. Yet I know it's working, because the method forces plenty of bubbles and coolant out through the bleed screw. So this doesn't seem to be my problem.

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[flash]

the hose at the top of the engine IS the return hose - it is returning heated coolant from the engine to the radiator, as opposed to the supply hose, which is feeding cooled coolant

so, yes, you would pull the upper hose

turning the starter will indeed rotate the pump, though only at 200rpm, so i don't know what the flow will be like

the holes in the thermostat alleviate the need to remove it, though again i'm not sure that 200rpm will provide enough pressure, but normally yes, it would need to come out if you were going to do the test cold, but it should be done hot

i used to have a bypass valve assembly for the MGBs that allowed me to install it, run the engine up to temp, and then conduct the test

they still sell the prestone "flush kit" insert - it goes onto a heater line and has a hose fitting - this was also a very cool way (pardon the pun) to find out if things were flowing properly

you really can't have much of a trapped air problem anymore, now that the thermostat is drilled - eventually it will all find its way up to the overflow tank - bleeding is still indicated, as it facilitates this process

hope that helps

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[Cloud9...68]

Thanks, Flash, that does clarify a lot of things. I think to cover all the bases, I'll go ahead and pull the thermostat, and put the supply hose (now that I have the terminology straightened out) back on. Then I'll pull the upper radiator hose where it goes into the radiator, have my wife start up the engine, and see how much coolant gushes out. Unfortunately, I'm running out of weekend (especially since my older daughter just called to ask me to pick her up - I'll sure be glad when she has her licence in a few months...), so I'll shoot for next weekend. At least I feel better educated about things, thanks to all the inputs.

And thanks for yor temp readings, John. Did you take them with a laser gauge? Yes, it's very odd that my lower hose is remaining cool, as it really doesn't seem possible. Yet I've had this exact same problem once before, and it was cured with a new, low temp (spec'd at 160 or 165, can't remember which) thermostat. The lower hose became too hot to touch afterwards, just as one would expect it shoud be.

I don't know why, and I wouldn't bet a nickel either way, but I hae a feeling I'm going to get a good-sized gusher of coolant when I run the test described above. I say that because the car is still perfectly driveable, as long as I drive it fairly moderately, even on hot days. It seems that this wouldn't be possible with a slipping pump impeller, although I suppose if one or more of the impeller blades has broken off, that might explain my symptoms. It's just acting as if the flow through the themostat is coming exclusively from the holes drilled in it, and that the thermostat itself is barely opening. But enough speculation; I'll let everybdy know how my test comes out. In the meantime, of course I'm open to any more suggestions. I hope whatever I find is of some benefit to the rest of the community.

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[Cloud9...68]

Well, here's a strange (but hopeful) update. I took it for a spin today around 5:00, when it was about 87 humid degrees out, and decided to do a few hard runs up to the redline, just to see how fast I could get the temp gauge to get up near 10:00 oclock, as it had done last time I drove it hard. It never moved beyond 9:00 oclock, no matter how hard I pushed it. And when I got home, the fat supply hose (the one leading to the water pump where the thermostat is housed) was actually pretty warm - borderline hot, in fact. So now I'm wondering if all this time, all I've had is some big air pockets that got into the system when I replaced the thermostat a few months ago, and have impeded the water circulation. Is this possible? I've never been all that confident in my ability to bleed the system, as it never seems to give off bubbles as long as I expect it to, so I'm never really convinced I've gotten them all out.

I think I'll rent the pressurizer again, and bleed it a few more times, maybe over the course of several days, with a lot of very hard acceleration in the process.

Does anybody have any tips on bleeding the system? I've always done it cold, and just attached a hand pump to the reservoir filler (where the cap goes), pressurized it to 10-12 psi, and then opened the bleed screw on top of the elbow in the front of the engine and waited until bubbles stopped coming out. Are there some steps I'm missing? I've heard of some people parking their car on an incline during the process. Does this actually help? In any event, my car seems to be mysteriously "curing" itself, as it has with so many other problems it's had. So I'm a little closer to believing I'm not going to have to yank the water pump, which is a good thing.

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[flash]

well, there is a problem for sure

put away the pressurizer - you won't be needing that, and in fact it can introduce air into the system

remove the bleed screw and make sure in is actually a bleed screw, and not a regular screw - a regular screw will NOT work - you can tell easily, as there will be a hole drilled through it, and the center is hollow - also make sure you have the fiber washer

reinsert the screw with the fiber washer and tighten down

get the car really warmed up - this won't work unless the thermostat is OPEN, so it needs to be fully warmed up and at operating temp - the best way to do this is to drive it

then put the car on a slight incline (like your driveway) - it's just to make sure the bleed screw is at the highest point

turn your heater to full hot - this opens the valve to the heater core and allows the coolant to circulate there

turn the fan on (low is fine)

crack the bleed screw until coolant comes out

close the screw

do it again

repeat process until is is a stream of coolant, and not bubbles

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[Cloud9...68]

Flash,

Thanks for the info; I'll definitely give this a try - the price is definitely right! Just one dumb question - do I open the bleed screw with the engine running, or with it off? Thanks.

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[JWahlsten]

Running. No pumping action with it off.

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[Cloud9...68]

That's what I thought. As first I thought the idea was to just let the air bubbles rise to the open bleed screw, but in reading Flash's description, it sounded like the pumping action was required to drive the air out.

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[flash]

yes - open with the engine fully warmed up and running - you are looking to see a steady stream of coolant to tell you there are no more bubbles or air escaping

do yourself a favor and put a nice absorbent rag in the area under the bleed screw, so that you don't have to smell coolant for a week

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[Johannvb]

I always bleed the system as described above, but also with the reservoir cap open. This means that you cannot drive the car until it is hot, because then you run the risk of blowing scolding coolant out of the reservoir when removing the lid. I just let the car idle until it is at full operating temperature.

I don't know if this is right or wrong, but it has always worked well for me and it allows me to keep adding coolant until all the air has escaped.

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[flash]

cap off can allow more escape, if the air is in that area, but it can also prevent full pressure, so stubborn bubbles may never make it out - you sort of have to play that one by ear - i choose to do it cap on first, and see how it goes

but then, i also always drill my thermostats, so it is pretty easy anyway

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