go to advance and buy a vacuum gauge. it is worth the money.
then u can also chedck the diaphrams

Good effort on the ducting.

I just want to say again that if you are getting 20-30 degrees of drop across the Carrera cooler that's normal. You might be able to extract another 5 degrees with improved ducting but your cooler is working fine already.

Forgive me if this question seems stupid, but are you 100% sure that the sender you are using is matched to the gauge? It's just that all you have been doing would only really yield minor reductions in temps, so there is either something majorly wrong with the motor or there is something really simple, like a bad gauge or mismatched sender.

I went through nearly the same exercise chasing similar symptoms - pretty hot all the time, really hot at the track ('84 Carrera).
Eventually I paid attention to the blowby escaping from the oil tank, did a leakdown test, and found three cylinders with broken rings.
Since the rebuild, temperatures are where they should be. I haven't been back to the track, but the temperatures in spirited driving are way down.
Might want to do a leakdown check.

Jon, the gauge was calibrated against the sender and is spot on.

Bob, I think you are probably right to some degree. But we did a leakdown (hot) and found really good numbers despite the high mileage, I can't recall but it was something like 2% all around! (more like 10% cold, mind you, but that's suposed to be measured hot, correct?)

I'll have to withhold judgement on the ducting until I install those heater backdate parts. I think the car runs hotter regardless, for not having airflow over the headers anymore... I also have a loaner SC distributor heading my way for comparison.

I'd love to measure vacuum but don't know what #s to expect, I'd really rather know what the advance should be with the vacuum connected, that would answer both questions at once (vacuum+dizzy). Still no dice extracting that info from the board though ;-) Could it be you guys are stumped ? (looks like something ATDC, which my timing light has issues with, reading BTDC only)

>So you still haven't verified the distributor?

That is the part where I mention that I don't live in CA anymore (where all the good dizzy guys are), I can't have the car immobilized for a month, and (just above) I have a loaner distributor coming this week so that I can get mine checked!

You can plot your distributor curve yourself by using a timing light that has an adjustable advance knob. It will take two people to do this, but by taking readouts of the timing knob on the timing light at various points of the RPM range, it will tell you if the mechanical advance on the distributor is working properly. Disconnect the vacuum lines when your doing this, btw.
Point the light at the TDC mark and turn the knob until the marks on the damper(0 degree) and Z1 line up. Read the dial on the light. This is your advance at the specific RPM. Repeat the process at various RPM's. 1000 RPM increments is more than enough.
this will not tell you if your vacuum advance is sticking or malfunctioning. It would interesting to see if you have the overheating problems while driving with the vacuum advance disabled.

WOW! This thread has certainly advanced in my absence. I
had a disastrous electronics month coupled with some sort
of allergic reactions to meds. Camera failed requiring research
for a replacement. One of the household TVs failed requiring
me to learn all about HDTV. My hard drive started failing
requiring replacement and reloading all the software (still
not complete.) Some of my files on my back-up hard drive
are corrupted also but I hope nothing too important (yet to
be addressed.

Greg, congratulations on your tenacity. Sorry it hasn’t (yet)
produced meaningful results. I see some good ideas above.

First, you are correct; heat exchangers should always have
cooling air going through them. Only if replaced with headers
(no heat exchanger) can you block off the air supply from the
fan shroud.

Disconnecting the supply air from the heat exchanger causes
the exhaust to run too hot. This can start a fire. It also raises
the temperature of the catalytic converter possibly leading to
failure.

Disconnecting the outlet of the heat exchanger allows too
much air to pass and reduces the engine cooling.

Using headers requires the air from the fan shroud to
be blocked off.


The picture above of the rodent’s nest shows that the
rearward cylinders (#1 & #4) can appear clean and forward
(#3 & oil cooler) can be restricted. Even a rag can do this
so look carefully. Noel is right on. There is a slightly separate
air channel in the fan shroud solely for the engine oil cooler.

Keep in mind it isn’t too difficult to do a partial drop and remove
the little plastic air duct above the cooler. This allows for easy
inspection of the air supply channel to the cooler and the
condition of the cooling fins. At this point it is very easy to
remove the cooler for inspection, cleaning and seal replacement.

There is an air deflector mounted on the back of (to the front
of the car) the alternator. It is possible for it to be mounted
incorrectly. Its function is to redirect the air flow to balance
the cooling of the 1-2-3 cylinders with 4-5-6 & the engine oil
cooler.

Greg said “- The cat is as good as empty so it's not an exhaust obstruction.”
Does this mean the cat can is empty? Is the ceramic catalytic
matrix missing? If so, where did it go? Into the muffler causing
a restriction? Just a thought.


Chris Bennet is correct, the 964 12-blade (curved) fan pumps
considerably less air but is quieter. Even not chasing the
specific problem, the 1.82:1 fan ratio using the 245 mm
11-blade fan improves the engine cooling. It also lets the
A/C work better.

Ron (Mysterytrain) brings up a good point about the
safety pressure relief valve in the thermostat assembly for
the front cooler. If that valve were stuck open then much
of the oil would bypass the thermostat and front cooler
altogether. Bruce Anderson and I both feel that this valve
opens about 100 psi and neither of us have seen one fail
stuck open. If stuck open, there would still be some flow
to the front cooler – possibly giving you these symptoms.

The vacuum advance/retard distributor on an ’80 and later
is very fussy. First make sure the hoses are in the correct
place. The hose you have labeled “Hose A” that points
toward the distributor body connects to the throttle body
port toward the rear of the car (and angled to the left). The
“Hose B” that points up and away from the distributor
body connects to the throttle body port toward the front of
the car and is shared (?) with a vacuum connection from the
Vacuum Booster (new in ’80).

http://members.rennlist.com/greg/911SC_distro.jpg



Originally the hoses were red (advance “Hose B” away
from dist) and blue (retard “Hose A” toward dist).

I would scan some diagrams but I can’t find my hp scanner
driver CD.

The point of this exercise is to have the ignition advance
controlled by engine RPM (centrifugal advance) and by the
engine load. The load “correction” is from the differential
net of the vacuum advance and vacuum retard The retard
has more effect (retard 8-12° @ 0.32-> mbar) than the
advance (advance 3-7° @ 0.32-> mbar). The advance and
retard vacuum also come from different ports on the throttle
body that are somewhat throttle plate position sensitive.

Whatever you do … don’t drive with it detonating.

Dave (WERK-I) is correct about using your timing light
to record the distributor centrifugal advance curve. There
is available a little hand-held vacuum pump and gauge that
can additionally tell you your advance/retard vs. vacuum
while the engine is running. Not an expensive tool.

Here is mine.

http://forums.pelicanparts.com/uploa...1162927011.jpg


Best,
Grady

PS: It took 2 hours and $48 software to get this done. I'm
still not even close. Still can't find the CDs for my scanner
or color printer. DOS was sooooo easy.
G.

Grady

You should be able to download your scanner and printer drivers:
HP Scanner Software

not to hijack..but Grady can you explain how that pressure relief valve on the external thermostat works??

Grady, my heart goes out to you on the HDTV stuff. The wallet-impact will make you feel like you got hit by a truck.

__________________________________________
¦
¦ I’ll delete this box tomorrow so we
¦ don’t clutter this thread.
¦
¦ flintstone
¦ Thanks, the download and install
¦ worked great (62 min with DSL)
¦
¦ Jon,
¦ Not yet a problem.
¦ The 26” Sony 720p was a bargain.
¦ I’m not ready for the big stuff.
¦____________________________________________


Ron, not a hijack at all. If this were to be a problem, here is the info:
"
http://forums.pelicanparts.com/uploa...1163010956.jpg "
© Dr. Ing. h.c. F. Porsche A.G.

1 – Plug for thermostat.
2 – Sealing ring gasket.
3 – Spring.
4 – Thermostat plunger.
5 – Plug for pressure relief valve.
6 – Sealing ring gasket.
7 – Spring.
8 – Plunger for pressure relief valve.
9 – Valve housing.

http://forums.pelicanparts.com/uploa...1163011000.jpg

I think the only failure mode I can imagine is for the seat seal
to decintigrate and go on th the oil filter. I have never seen
one even damaged.


Sometime this winter I’ll do a complete thread on oil coolers and thermostats.

Best,
Grady

Ok, so the pressure relief is the first thing the oil sees. If the pressure is greater then 100 psi it redirects the oil and saves the front oil cooler from bursting. The thermostat prevents oil from flowing to the cooler until it has reached 180/190 or so. Yes? No?

I don't believe the thermostat is a pressure sensitive device by nature. The parafin plnger is temperature sensitive only and directs oil to cooler when temps reaches 185 degrees. The plunger is marked with the temperature in Celsius. The oil filter is a pressure sensitve device and does not filter when oil is cold and flows poorly.

Guys,

The ’74 and later “thermostat” assembly has two separate components; a thermostat and a bypass pressure relief. They are un-connected except they are in the same housing and operate on the same fluid.

The pressure relief operates before the thermostat. It only senses the differential pressure in the thermostat assembly. If the line to the tank was restricted or the filter restricted, the pressure relief wouldn’t sense that.

Without a pressure relief there are situations where the front cooler can be over-pressurized and fail. This is what can happen on a ’73 only system (no seperate pressure relief) with a finned cooler in place of the “trombone.” The typical situation happens when the engine is parked hot and allowed to get fairly cold overnight or over a long period. When re-started, the scavenge pump is pushing 100% oil through the system until the crankcase is evacuated. The oil is also cold and highly viscous. Without the pressure relief valve the mechanical pressure limits can be exceeded and the system will fail at the weakest point – usually the cooler or a hose connection.

The thermostat operates by restricting the oil flow as it returns from the front cooler. There isn’t any change in restricting the flow to the cooler.

The thermostat element senses the temperature of the combined hot oil from the engine and the cooler oil being returned from the front cooler. This allows it to attempt to maintain a constant oil temperature of the combined oil returned to the tank. This only happens when the front cooler has more than sufficient heat transfer capacity.

The issue with most standard 911 front coolers is insufficient heat transfer capacity. In this situation almost all of the oil is going to the front cooler. Baring a failure of the pressure relief valve seal or it sticking open, the only oil to not go to the front cooler is the (slight?) amount leaking between the barrel of the thermostat plunger (#4) and the valve housing (#9). Of course there is some (slight?) heat transfer through the aluminum housing from the hot oil to the cooler oil returned to the tank.

If I were installing a new or used thermostat assembly, I would disassemble it and inspect all the machining, clearances and passages. It is possible for something to be machined incorrectly, be obstructed or fail. Once in place and functioning correctly, I wouldn’t ever expect a failure. It better be - considering how difficult it is to get the fittings off without destroying the housing. :D


Given that there is hot oil going to Greg’s front cooler and there is a temperature differential across the front cooler, that tells me there probably isn’t an issue with the pressure relief or thermostat.

Lets help solve this heat problem.

Best,
Grady

great writeup Grady. Thanks.
The only way then barring the above mentioned plunger restriction, would be to hook the oil lines "from engine" and "to tank" reversed. Correct?

Thanks Grady..that clears up the functionality of that little bugger.

I have a stupid question. After reading all of this, no one has asked what oil is being used. I can't imagine he is running 50 weight oil, which when hot would thin out some but who knows. Great thread, and I am learning alot but would like to see what the problem really is. If possible, I would like to see him replace the muffler for a test and have yet to read where the cooler at the engine was clean and clear. My .02 and may be worth even less. Good luck. Spencer

>If possible, I would like to see him replace the muffler for a test and have yet to read where the cooler at the engine was clean and clear.

So would "he" (like to see the cooler) ;-) I sold my lift recently and haven't bought another yet ($$$) and my car is low so I cannot really check the cooler. (I'm not using jacks ever again after one garage floor tile unglued itself fromt he weight and almost dropped a 993 on my head). I will probably get to take a look on someone else's lift this week end and blow compressed air through the bugger. I'll take pictures...

As for the muffler, I am considering a set of SSIs for an 83 SC (thick flange, O2 sensor hole) so feel free to recommend one. I don't think it'll happen "now" but in the future, it's possible !

I was told my catalytic converters had been gutted and therefore I kinda doubt there is much obstruction in the exhaust system. But you never know !

No disrespect here - but if you are not sure do not assume, terms like 'I was told' are red flags. I would remove that cat and inspect it. Assume nothing.