2.7 911 head studs - again
 

Would appreciate your thoughts:

I have a 77 911S. Owned 30 plus years. 110K. Original. Only improvement are clutch, tensioners, pop off valve and plug wires. Nothing else. It runs fine. I drive like the old man I am increasingly becoming.

I fret about head studs. Intend to keep the car and want to pass it along. Questions:

1. Might I currently have one or more broken head studs. If so, how would I know?

2. Any thing I can do to reduce likelihood of breaking studs?

3. Should I just drive the car and stop worrying?

Would appreciate your thoughts.

Thank you.

The 77S mag case from the factory has steel studs.
The fast expansion of the cylinders has a tenancy to pull the steel stud out of the mag case
The fix in the 80/90s pull the steel out, install inserts and replace studs with dilivar
This requires a complete disassembly because the drilling and tapping produces chips of magnesium everywhere.
Suggest, if there is no known problem, keep driving the car.
The mag case, on rebuild far exceeds the value of the used engine.
I, for years, have suggested to my friends get a 3.0 because build costs are way less on the aluminum cases but broken dilivar are always a possibility and reason to replace with steel studs.
Bruce

In magnesium cases, we use Supertec head studs with CaseSavers and have had zero reported failures over the last 20+ years.
Quit using Dilivar when we had brand new ones break on the engine stand before the engine ever ran.

As an air-cooled Porsche only engine shop, we see all kinds of engines with varying mileage and rebuild quality. To this day, I have rarely taken apart a mag case 2.7 with Dilivar studs that didn't show head to cylinder instability.

The problem is not the studs but the engine running too hot with the thermal reactors ,
5 blade fan and higher temperature oil thermostat . Fix these things and don't worry about the rest .

Richey - those things don't help, but 3.0s can have exhaust studs break even without thermal reactors.

I agree with the advice that as long as your head studs are good, just keep driving, and check every once in a while. Lots of us have driven unknown miles or hours with a broken stud. Some with more than one. Could that cause extra damage? Yes, but not catastrophic usually. Now if you want to rebuild the engine - freshen up valve seal, deal with leaks, improve leakdowns/compression numbers, replace bearings, or to hot rod the engine - well that falls into a different category - of course insert the case and replace the head studs. Marginal cost at that point isn't that great.

Thank you. The car does not have thermal reactors - I don’t think it ever did. It has an eleven blade fan. The majority of the time it runs about 170 degrees. Rarely gets to about 210. I guess that’s not excessively hot?

Oil temperature thermostats
 

David:

Oil temps of 210*F are just fine, especially so with modern synthetic oils.

The thermostats seem to open at 190F, more or less, from my observation. There is a school of thought that you don't want to run all the time below 210, because then you won't boil off any water which has gotten into the oil - and some does despite the car being air and oil cooled and not water cooled.

I wasn't aware that Porsche changed the opening temperatures of its thermostats, so I looked into my Factory Shop Manual. Starting with the 1969S there are two thermostats - one in the engine, one external for the front cooler. Both involve wax heating up and pushing a sort of piston out of a capsule. While the two thermostat housings are geometrically different, the capsules are the same in both. The parts manual gives a part number for the capsule in the external thermostat, but not the engine mounted one, which is just shown as a complete unit.

The early engine mounted thermostat units had a screw adjustment extending out the top of the unit. You can see this in the pictures in the Volume I shop manual. I suppose if that adjusted the capsule position relative to the valve it controls that might affect the opening temperature? The factory manual makes no mention I could find about adjusting anything with this. It does say the original thermostat is set to open at 80*C (176*F).

Starting with the 1969S model (first to have a front supplementary oil cooler), the front cooler thermostat opens at 87*C (189*F). The engine thermostat opens at 83*C (183*F).

I've tested these thermostats and capsules, but just using a refrigerator for cold and boiling water for hot. Those were go/no go tests to see if a capsule had quit working (which they do) or not.

Not a word is said about that mysterious adjusting or something screw in the early engine thermostats. Unlike the external thermostat, the engine one is not set up for straight forward disassembly, though I have seen reference to being able to do that.

I know a '77 thermostat for a California car has a different part # and opens at a higher temperature . And I know the engines will run cooler if the thermostat , 5 blade fan and thermal reactors are changed , I own one .

Interesting - my downloaded (from Porsche) PDF of the PET parts catalog for 74-77 shows the remote thermostat capsule and the engine thermostat as only being one number. As opposed to the fan, for instance, where reference to California is found. Same in the genuine printed catalog I acquired before the days of those being posted on an Internet site.

Walt: it’s nice to hear that 210 is not a problem for modern synthetic oils. I run old school Castrol 20/50. Should I switch to synthetic?

I've never researched the parts catalogue , but my '77 was a different # than a '74 I inspected . I think Bruce Anderson referenced this in his book .

I won't get into a "what's the best oil" discussion. Cars ran pretty well on dino oils for years as long as they and filters were changed frequently. No reason they shouldn't still. However, synthetic oils possess a consistence dino oils really can't match.

At a tech talk at the 2000 Porsche Parade in Sacramento, a Mobile Oil engineer explained where synthetics came from. The B29 bombers had a problem landing - the grease in the axles of the wheels hadn't thawed from their high altitude flights when they touched down, so a lot of tires were flat spotted. Mobile came up with a synthetic grease which either didn't freeze or thawed a whole lot faster. Part of its magic was the fact that the molecular hydrocarbon chains (polymers?) were all of the same length. Turns out, they were also more resistant to breaking and getting shorter as well. Which is why oil change intervals these days are longer generally.

The big differences between brands are the additive packages, which neutralize the effect of contaminants which get into the oil from the combustion chamber. These in effect wear out over time. The actual lubrication function apparently doesn't really degrade much. These packages are proprietary as each oil company's chemists strive for a better mousetrap.

The most recent issue (now not all that recent) is the level of zinc in the oil. Environmental concerns led to reductions, but operational concerns - especially in our air cooled motors with rocker arms and not lifters - have led many to find oils promising higher levels of ZDDP. I use whatever Mobile 1 Porsche recommends in our 07 Turbo, and Valvoline Racing oil in our track only cars. I used to use Mobile one there, but they lowered the zinc additive. But others use other oils with no issues either. As with many things about our beloved Porsches, there is seldom any one consumable which is objectively the best, and even where pretty scientific comparisons can be made, many sub-optimal things work just fine too. This is especially true for street cars.

210 degrees just isn't all that hot. Engine efficiency is said to increase with heat. At some point wear also increases, so there is a balance somewhere. Bruce Anderson (RIP) used to say that something (over 210 as I recall) is OK, but 250*F is "too damn hot." Well, the oil I use in our GMC5500 turbo diesel tow vehicle is a Delvac brand which advertises standing up to really high heat - 500 or 1,000 degrees? I forget, but way way higher than anything in my SC.

If you don't own it, I recommend you purchase Bruce Anderson's Porsche 911 Performance Handbook 1963-1998. It is full of nuggets - for instance, he mentions Porsche changing the opening temperatures of the oil thermostats over the years. I've read his book cover to cover several times, and look things up often, but I'd not spotted this until just now - since it was mentioned in this discussion. You'll learn a lot.

Bruce died a couple of years ago. The ever helpful Bruce Anderson who helps guys out here on Pelican is unrelated, but equally invaluable when we have problems and questions.