Help with 68 Normal engine - temps sensors specifically ?

[Greg D.]

Tiny bit of background... Friend of mine, 356 guy, bought his first 911 - a 68 normal, and has not joined this merry bunch yet. The gauges threw me off because the car has no 911 oil pressure/oil tank level gauges at all, the temp gauge is identical to that of my 68 912. Now he's trying to diagnose the high temps he's seeing and he's come up with the temps sender on the left side of the engine... Yet, every manual he sees has the temps sender on the right side ! and indeed he thinks he has 2 temps senders, both with wires.. yet the left one is the one currently operating the gauge...

This is a horrible picture and I apoligze, just meant for "vague" reference:



At the end of each stick (or thereabout) is what he thinks is a temp sender. Both are connected to green with black wires. The one to the left is the one running the gauge. The one on the right has a wire that lays across the engine under the air filers (but still looks factory). Whenever he tries to get photos of the temp sender on line he gets the picture of the one on the right. In fact most pictures that provide a clear view of the engine do not even show one on the left.

Anyone well versed in 68s knowing what's what ?

[edmayo]

I have NEVER seen a temp sender on the left. What I don't see is the pulley from the left cam for driving the air pump belt. Is this a Euro market car? On some SC's there was a thermal switch located in that chain housing cover, does it have that cover installed? There wouldn't be enough oil flow there for a temp sender, he still needs to use the normal location on the right side.

[304065]

Ed nails it. The chain box cover on the left is from an SC. If there is a sender there, the other end is sticking out into hot air!

The sender location is over right next to where the engine number is. It's at the end of the main oil gallery.

Now comes the fun part-- the resistance range of the OLD sender is 100-200 ohms, which does not provide a lot of variability! The new (LWB) sender is 18-1000 ohms. The old sender is well over $150 these days, maybe even NLA! The new sender is like $15. But the trouble is, the difference in resistance range means that the gauge must be modified in order to work with the new sender.

Once your pal figures out the sender puzzle, then it's time to look at why it's running hot. First thing is to check the advance-- I see he has the vacuum retard distributor, good! That is a '68 piece. But the old distributors are prone to wear, giving about 40 degrees of advance, which will break the top rings from detonation, and the engine will run like this:



So check everything out as soon as possible before putting too many miles on that motor! Good luck and tell your bud that Irish Green is always welcome!

[Greg D.]

Thanks for that. That was puzzling me, too. I know he checked it at 30 degrees of advance at 6000 rpm so hopefully no broken rings. Honestly if I could not see the gauge I'd never guess it runs hot, it feels like a good solid strong engine, but we need to know for sure. So time to de-turkeyfy the car then, and move the gauge wires over to the correct (and possibly defective) sender... Your help is very much appreciated, I'm worried he might give up on 911s and go back to 356s only ;-)