Just wondering if the 3877660 thermostat housing is correct for a '70 SS396/350 HP?

Thanks a lot! :D

That is the correct number for a 70, but there are two versions out there with that number. My understanding is the `69 version has the number down along the edge near where it meets the intake manifold. The `70 version has the number on the area (tube) that the upper hose attaches to.

I can't claim this to be absolutely the case, as the 69 version may have crossed into the 70 model year, but it's just what I've found on a few cars.
Others may chime in with more exact info.

Thanks, Rick, I appreciate it! :D
My understanding is that the originals have the part # on the front lip and the replacements have the # on the neck.
It would be nice if someone would clarify this.

This is something I save from an Ebay ad, Dont know how much fact is here. Just thought it was good reading.

THE “660” THERMOSTAT HOUSINGS USED WITH ALUMINUM INTAKE MANIFOLDS WERE NEVER PAINTED FROM THE FACTORY
AND HAD THE SAME STEEL SHOT FINISH AS THE FACTORY ALUMINUM INTAKES - A PROCESS USED AT THE FOUNDRY TO GIVE A
NICE SMOOTH SHEEN FINISH TO THE ALUMINUM WHILE RESISTING AGAINST STAINING FROM CHEMICALS OR DIRT AND DAMP
WEATHER CONDITIONS

ONCE THE ALUMINUM IS GLASS BEADED THE STEEL SHOT FINISH IS GONE LEAVING A DULL OPEN PORE SURFACE ALLOWING
CHEMICALS OR DIRT AND DAMP AIR TO STAIN OR ETCH THE BARE ALUMINUM

THE “660” THERMOSTAT HOUSINGS USED WITH CAST IRON INTAKE MANIFOLDS WERE PAINTED WITH THE ENGINE AND INTAKE
MANIFOLD DURING ENGINE ASSEMBLY AT THE FACTORY

GM USED SEVERAL DIFFERENT BOLTS WITH THE “A” “M” “TR” “RSC” “WB” HEADMARKINGS DURING 1969 AND 1970 MODEL YEAR
ANYONE OF THESE HEADMARKINGS COULD HAVE BEEN USED AT ANYTIME DEPENDING UPON SUPPLY AT THE VARIOUS
ASSEMBLY PLANTS DURING THE 1969 AND 1970 PRODUCTION

THE GM 3877660 THEMOSTAT HOUSINGS USED DURING 1969-70 MODEL YEARS WERE CASTED WITH SEVERAL PHYSICAL DESIGN DIFFERENCES WITH OUT ANY PART NUMBER CHANGE FOR THE “660” WATER NECK AS FOLLOWS:

• PART NUMBER CASTED ON BASE
- 3 ALINGMENT DOWELS IN RECESSED AREA’S
- 1 ALIGNMENT DOWEL NEAR LONG BOLT HOLE TOWER

• PART NUMBER CASTED ON BASE
- NO ALINGMENT DOWELS IN RECESSED AREA’S
- 1 ALINGMENT DOWEL BY LONG BOLT HOLE TOWER

• PART NUMBER CASTED ON NECK
- SMALL LETTERING –
- NO ALINGMENT DOWELS IN RECESSED AREA’S
- NO ALINGMENT DOWEL BY LONG BOLT HOLE TOWER

• PART NUMBER CASTED ON NECK
- LARGE LETTERING
- NO ALINGMENT DOWELS IN RECESSED AREA’S
- 1 ALINGMENT DOWEL BY LONG BOLT HOLE TOWER

THERE ARE TWO MORE CHANGES WITH LATER GM “660” THERMOSTAT HOUSINGS BUT ARE LATER PRODUCTION AND ARE
PHYSICALLY DIFFERENT AND INCORRECT FOR 1966-71 MUSCLE CARS AS ARE THE REPRODUCTIONS THAT ARE BASED OFF
THE LATER GM SERVICE REPLACEMENT HOUSINGS

This is something I save from an Ebay ad, Dont know how much fact is here. Just thought it was good reading.


Interesting, thanks!

"THE “660” THERMOSTAT HOUSINGS USED WITH ALUMINUM INTAKE MANIFOLDS WERE NEVER PAINTED FROM THE FACTORY AND HAD THE SAME STEEL SHOT FINISH AS THE FACTORY ALUMINUM INTAKES - A PROCESS USED AT THE FOUNDRY TO GIVE A NICE SMOOTH SHEEN FINISH TO THE ALUMINUM WHILE RESISTING AGAINST STAINING FROM CHEMICALS OR DIRT AND DAMP WEATHER CONDITIONS"

Steel shot blast was used to clean the casting. When the casting has solidified and cooled, the sand core must be removed by applying hammering to the casting (called knock out). There is a thick boss on the casting that hammering is applied. Once the sand core is removed the thick boss is sawed off and trimmed of flashing. Shot blast cabinets are used to clean any remaining sand and also smooths the finish.

The customer had an internal cleanliness specification that had to be met. Shot blast helped accomplish this.

Shot blasting had no benefit in preventing staining or changing weather conditions.