Speed, Heat and Timing
 

O.k. ... here's a question for experinced 912's. My '67 runs near perfectly. Starts easy, revs right up, idles steady and smooth at cold or warm, plenty of power for normal driving. Why then if I try to cruise at high rpm .. 3600 to 4200 (about 70 mph and above ) does it heat up too much. I haven't checked timing advance but really it runs so good with moderate use. I have an unidentifiable dist. .. can't find any stamp on it. All sheet metal is in place. The belt is not slipping. Must be the timing ? Help!

To begin with the type of dist.would be stamped on the body of the dist. the last 3 digits being the relevent ones; example .031, .009 or the high bread .050. More than likely your timing is off, this can cause air cooled engine who tend to run a little hot anyway to over heat. Find out what dist. you're using and set it to spec. Other causes could be to lean a fuel mixture, dirty or defective oil cooler. Timing is very important though, get that together first.
Chas.
69/912

Can you take/upload a digital pic of the distributor? If nothing is stamped on the body, maybe we could identify it with the pic.

Jason
'68 912 Coupe

I agree worst situation is colloged oil cooler...

Hmmm needs to be investigated.

M:confused:

I agree with 912UK-check your oil cooler for debris. You would be surprised what you find back there. Is your sound insulation flaking off from the engine compartment? If it is, it will wind up at the oil cooler. by the way, how hot is it running at 4K?

I don't think it's debris on the fins. The engine compartment has been clean of everything since well before I acquired it and during my troubles with the generator I saw nothing inside the fan cavity although I was looking through the port. Don't know actual temp but after cruising at 3300rpm the temp levels off at about half way on the gauge on 75 dgr F days but will continue to climb towards the danger zone if I push it up to 4000 rpm. This weekend I'll try to get a better look at that "dizzy" and the springs that control advance. I have electronic ignition and an electric fuel pump. Maybe the fuel pump is slightly starving and making it too lean at high RPM ?
Thanks for you interest guys. It's been raining here almost steady all spring so can't drive much.
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I noticed a similar thing with mine awhile back. During the cooler weather I never had the temp gauge go beyond 1/4, but when the temps outside began to climb into the upper 80's and low 90's I found that sustained speeds of 70 or higher would bring the gauge up to almost 3/4(still not in the red zone but a lot closer that I liked) I reset my max advance from 32 down to 28 and now she will run at halfway at 70mph on a 90 degree day, still warmer than I'd like though. I also checked out the cooler and it is clean as a whistle, a small plastic "zip" tie is what I used to go through each air flow hole on the cooler to verify nothing was blocked. I'm also considering going to a lower viscosity oil, I currently run Castrol 20/50 but I may try to go back down to 10/40 since I wonder if the heavier oil isn't losing enough heat going through the cooler. Just some thoughts...

Kevin,

You might be going in the wrong direction with your oil. From what I hear, warm weather is a good match for 20/50. What Castrol are you using? Syntec? (That and Mobil 1 20/50 have been written up by the Maestro and others to give the coolest ride in hot weather).

Just some thoughts...

Jason

Kevin,

The Maestro used synthetic oil in all his cars, but it seems real hit and miss on the 912. You can do well by it or introduce more leaks than the Exxon Valdez.

I say stick with the Castrol 20/50 and look elsewhere for possible causes.

Craig

Unless your engine is new or has all new seals I would avoid synthetic oil, the stuff is so slick it slips through everything, and with a side banger thats a bad thing.
Just my opinion,
Chas.
59/912

Some success. I set back the timing a bit and it seems to run a little cooler. What I actually noticed is coming over the mountain today on my way home , after trying to heat it up on this 75 dgr day,
I climbed this steep long grade in 5th with no pre-ignition ping. Might have more torque due to lower advance.

Experiment ... it's a good excuse for screwing up!
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jac,

Being in the Northeast I wonder what humidity does to your engine temp......anything????

Craig

If you do any flying one of the first things you learn about is the 3 H's High, Humidity and Hot, all bad for HP and lift, thats why the runways are so long in Denver. Remember thinner air does not cool as well.

Craig

On the oil subject ... got to find a happy medium depending on ambient temp and usage. The oil does two critical things. Cooling and lubricating. If all you cared about was cooling you'd run antifreeze. A low viscosity oil will lubricate a cold engine nicely because it flows easy but if it heats up it will break down. Never considered that a thin oil would loose heat faster than a thicker oil. In summer I use 20/50 ... and I don't think it matters what brand.

More experimentation. After setting back the timing (no timing light avail. ) It runs great and cooler. EXCEPT ... I ran it up to 4200 rpm tonight and it started missing and would accelerate no more.It maxed out at 4300 and about 80mph. Worse .. the temp climbed rapidly to near danger. Did I retard the spark too much? Seems like it was choking out . Pipe show a lot of soot. Too rich make it run hotter?
Thanks for your help guys. I know my next tool will be a good timing light.

A Sears "Magic Dial" is a good timing light. You need one to set your timing where it should be.

You need a timing light and lean runs hot.
Chas.
69/912

Ok ... reset the timing right by the manual. Ran perfectly awesome. And then got hot at 3800 rpm. Started at square one. LOOSE BELT !
Well I saved the price of a timing light.
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A good timing light with advance knob on it is one of the most valuable tools you can have for your 912.

Put that at the top of your 4th of July gift list, Christmas is to far away and fathers day is already past.....

Craig