Have I done any damage?

[RoninLB]

Tim...good post...I use the dual ga. 2DA8 ...I run about 210deg in NY all year long...in deserts, on big rides temp moves up slightly if I drive according to conditions..meaning the stock 2.7 runs best between 3.4k and 3.8k...if I don't CHT will rise quickly...especially on big hills in high desert areas...a good example would be comming into Los Angeles from the north..the mountain pass/high ambient temp/slow traffic will cause head temp to rise to high[IMO] when using 5th gear at 60 or 65mph..so I downshift to 4th before oil temp gets high...the CHT reacts immediately...IMHO, if I wait for the oil temp to rise it's to late...turbo 911 is another story which I don't have.....I'm not a pro on this, just trying to do my best..........Ron

[Early_S_Man]

If you don't mind doing some scrounging through dusty parts bins ... you can sometimes find some good deals on military surplus gauges at dealers like GEM Aircraft Supply in Dallas!

This one was for a Boeing B-50, and cost me $10! It also has a decal of the complete gauge circuit on the side, and uses the same thermocouple probes Westach or Aircraft Spruce sell!

[pbs911]

So what is too hot for the CH temp? 200? 250? 300?

[Jim T]

Originally posted by pbs911
So what is too hot for the CH temp? 200? 250? 300?

I think CHT's run much higher than that on an air cooled engine.

At least on Type IV's, CHTs normally run around 350-425 F, from what I recall. I'd think a 911 would be similar.

[Bill Douglas]

And.... After a few hours of driving with a new belt check it again. My new Porsche brand belt stretched alot in that time and needed to be readjusted.

[speeder]

Jim is correct. Don't ever confuse CH and oil temperature. The heads run a LOT hotter, hence the quick damage from lack of air-flow(broken fan belt).

[pbs911]

I think CHT's run much higher than that on an air cooled engine.
I'd think a 911 would be similar.

Then I must ask, is Warren's guage useless? Nevermind, I just noticed it is in Celsius.

Nonetheless, I would like to get a CH tempt guage with the red in the right location. Anyone know the limits?

[Joeaksa]

Paul,

Warrens gauge is in Celcius... will work fine. If it works on a B-50 (a improved B-29) radial motor, then a 911 is no different.

Joe

[304065]

I don't think it's useless, the scale goes from 32F to 482F.

Plus it adds that boneyard, cold-war cool! All he needs now is an "eyebrow" or "post light" to illuminate it at night.

Also, it's a hell of a lot cheaper than a TSO'd, or even experimental grade version.

http://www.wpafb.af.mil/museum/outdoor/od17.htm

VDO makes one also, if you really wanted to you could have North Hollywood Speedometer silk screen a "Green Arc," "Yellow Arc" and a "Red Line" on the gauge, depending on the specs from your particular model.

http://www.nhspeedometer.com/cockpit_page1.htm
(Scroll to bottom)

[RoninLB]

the temps I gave on a previous reply is w/probe that is placed on spark plug in place of plug gasket.......Ron

[Zeke]

Phoenix, I'm glad to see that you are going to have a pro look at your motor, but if it makes any difference to you, I too, drove a 911 a couple of miles w/o a fan belt, coasting and restarting. No damage. Drove the thing another 80,000 miles after installing belt.

[autobonrun]

Instead of monitoring alternator voltage, monitor the head temperature by placing two multipoint thermocouples on each bank of cylinder heads (six total). Plenty of space behind the fan, just need to attach them so that the tip of the TC is in the fin.

Then take these signals to a high selector which will select and transmit the highest of the six temperatures. With the highest head temperature now available, the signal could then either

1) light a light at a preset temperature
2) drive an indicator which will display highest cylinder head
temperature

or even

3) Connect the switch to a relay that will shut off the car. Temperature switches are available with multiple setpoints so that at the lower setpoint, the light would come on and at the higher the car would shutdown. This way it would be no surprise and possible save a $5K rebuild.

You could probably assemble all the parts for less than $350. Other than fixing the thermocouples to the head fins, the remainder would not be that complex. Fish the thermocouple lead wires out into the engine compartment and mount the signal selector and switch there.

[Phoenix]

I'm breathing easier again today and will definitely sleep better:

My mechanic just phoned with the test results:
Leakdown = 2-3% all around
Compression = 150-170

Man I can't tell you what a relief this is! I was expecting the absolute worst.

Nest steps:
- Oil change
- Valve adjustment
- Replace the rocker shaft O rings (may be causing the leak)
- Upgrade to Turbo style valve covers (orginal magnesium ones are a little adding to the leaking)

I'm also picking up an 8mm allen wrench, matching box-end and an extra 24 mm box wrench so that I can change teh belt myself should this happen again.


I'd like to thank everyone who responded with thoughts/ insights & direction. I was lucky this time and am definitely better prepared now. You guys are lifesavers!

[Wayne 962]

Running without a fan belt is akin to running a water cooled car with zero water.

Six shims is a good rally cry. I have heard of the five shims before, but the rule of thumb is that if you have six, you're good for all 911s...

-Wayne

[Kurt B]

Because of warren typing in all caps and bold: "don't ever drive with a broken fan belt" the one time mine broke, I shut off the car the second the alternator light went on. I saw the light immediately and knew what it meant.

Thank god for this forum. And no, I wouldn't have known that I couldn't just drive it home if I hadn't been forewarned by warren on this matter. Thank god for this place.

[Rot 911]

Oliver, I think we all are breathing a sigh of relief for you.

[Doug Zielke]

This is a great thread!

I did build my prototype Broken Fan Belt Warning Howler, and tested it last night. The Sonalert I used would wake up the dead!

However, after looking at the Westach website as recommended by Tim T, I think I will spring for a nice, dual CHT gauge to replace the dashboard clock. Thanks for the excellent link, Tim.

[dougcl]

Curious. I've had a CHT gauge for years, mounted where the radio is supposed to be. It's made by VDO, and the thermocouple has a washer that fits underneath one of the sparkplugs. I use plug #1 since I was told that #1 typically runs hottest. At cruising, I see about 225F typically. Really hard runs uphill will push it to 300F, coasting downhill can drop it to 175F or so. My oil temps are typically 180F, but it will get to 195F on hot days (street driving).

Doug Clauder
1975 911Shttp://members.rennlist.org/dougcl

[derek murray]

regarding CHT gauges.... pelican also sells them, which by the I have quickly added to my parts list.

PP part # VDO-310901

great thread BTW

[Leland Pate]

Oliver...

The P-gods have smiled on you!!!!!!
Congrats! I felt aweful after reading your story... it reminded me of my missed shift here a couple months back.
So, I can relate!!!

As for the discussion about the CHT gauge.
It is interesting that someone would say that the #1 clyinder typically runs hotter than any other... At first, I thought... naaaah.... but after I thought about it... I bet it could due to it's position in relation to the fan! The air guides on the back side of the alt. are supposed to direct air to where it needs to be, but I'd bet there's no way it could get equal the volume down to the #1 and #4 cylinders as well as the others... this has prompted me to move the thermocouple to another cylinder and give it a try.


And on aside note... After warm up I get a steady 250 degree reading from my VDO CHT gauge with the T.C on the #5 cylinder.

That is the hottest i've ever seen it get. Driving fast... slow... uphill, down hill... that is where it always settles.