L78 Thermostat short bolt required

[Gary C.]

Hi,
I am looking for a 3/8" UNC bolt, 16 x 1 5/8" long with "P" or "M" headmark for the thermostat housing on my 65 L78.
Any idea as to where I can get one?

Thanks,
Gary
Perth Australia

[William D.]

Re: L78 Thermostat short bolt required

Richard Fortier - He advertises in the Driveline!

[Daniel K.]

Re: L78 Thermostat short bolt required

Richard Fortier - He advertises in the Driveline!

Wonderful! I need the long one. Thanks for the info. Also, need some advice on removal. When I tried to remove this bolt, it would twist and I fear that I will break the bolt. Do I give it a few taps with a hammer or use impact wrench or what? Don't want to damage the Winters manifold either. Dan K.

[Timothy B.]

Re: L78 Thermostat short bolt required

Daniel,

Get your propane torch, heat the bolt and melt some candle wax into the hot bolt threads if you can get to them. If not, try some kroil or liquid wrench to lubricate the threads.

Watch the gas lines..

[Rich P.]

Re: L78 Thermostat short bolt required

Gary,

the 1-5/8" P or M is the easy one to find. The hard on is the grade 8 CP 3-1/2". Do what ever you can to save this bolt. It's only use was on 65 396's and 67-69 L-88's!!! The repro bolt can be spotted easily.

Rich

[Gary C.]

Re: L78 Thermostat short bolt required

Rich,
These are the two bolts I have. Lost 2 points in the NCRS judging here in Oz. I assume the CP one is ok?
What do you think?
Thanks,
Gary

[Jack H.]

Re: L78 Thermostat short bolt required

You've got the one grade 8 bolt that's virtually impossible to find and I seriously doubt there's anyone doing judging in Australia who's got sufficient experience with these rare 396 cars to be able to distinguish between a factory original grade 8 CP bolt and the current reproduction given how rare this part is!

Why is it rare? What called for the use of a grade 8 fastener to simply hold the thermostat cover down? This is a subtle aspect of the lore of owning a 396 car...

Flip your copy of Noland Adam's Vol 2 book to page 278. There you'll see an early prototype L78 car from the Milford Proving grounds. Note its radiator expansion tank bolts to the THERMOSTAT COVER and there's a bracket holding the overflow hose affixed to the fan shroud via a clamp. That was the initial design that never went to production!

It's why the one bolt on the thermostat cover needed to have grade 8 strength and why savvy 396 judges run their fingers under the fan shrouds of EARLY cars looking for a hole in the plastic beneath the 'Caution, Fan' label (hole for the radiator hose clamp bolt).

Then, flip to page 283 and you'll see a close-up of the grade 8 CP bolt as well as a confusion factor on page 280. There, the upper picture shows the thermostat's short bolt as having a blacken finish while the lower picture depicts a silver colored short bolt.

The general consensus is that the heads of both bolts were shot with the silver paint used to cosmetically match the thermostat housing to the aluminum intake manifold. It's suspected the car in the upper picture must have seen tech service/work...

Don't let the date on these pictures fool you. Its when the pictures were taken and not when these cars were built. Note the upper picture says June of '65 and the car has a curved neck radiator but the lower picture says August of '65 and that car has an early straight neck radiator in it!

[Gary C.]

Re: L78 Thermostat short bolt required

Thanks Jack.
So I just have to find the M or P head bolt.
I have a 1" M head bolt. Would the head on the 1 1/2" bolt be the same?

[Ronald L.]

Re: L78 Thermostat short bolt required

Gary,
If you are chasing two points...

I have a couple ideas from the picture you posted.

1. The orange paint on the by pass hose, should be some but like a rattle can was pointed at it? On the aluminum intake I defer to these 396 experts on what that should look like.

2. The hose and hose clamp - hose looks too thin, was this supposed to be the #10 hose clamp? IMHO the repro's are way off this day in age and you need to get the real parts which are out there see the thread from John M. on this last week.