1966 and later BB thermostats

[David L.]

Re: 1966 and later BB thermostats

Ron,

Here is a picture of a NOS 3156280 180 degree thermostat that I sold on Ebay earlier this year. It is stamped "CF" and "DELCOSTAT" on the top and "180" and "HRD" on the bottom. GM # 3156280 appears in my 1963, 1964, 1965, 1966, 1967, 1968, 1969, 1970, and 1972 Chevrolet parts catalogs. As far as I know this was the thermostat installed at the factory from 1963 to 1972 on all Chevrolet V8's that used a 180 degree thermostat.

Dave

[Ronald L.]

Re: 1966 and later BB thermostats

Hi David, thanks for posting. I doubt what is in the car is this part, won't know until I take it apart, but very interesting to know that my '74 parts book specifies this part number as being a 170 degree thermostat.

On a 60- 64 degree day at 70 - 80 MPG, the temperature sits at about 205.

My idea is that moving up the opening point to 200 (180Dthermostat) will inherently raise operating temperatures given constants in the balance of cooling capacity, time, velocity, engine RPM, etc.

With a big block once you get it warm, about 10 seconds, then you need all the cooling you can get, unless it is 30 degrees out side...

[Joe L.]

Re: 1966 and later BB thermostats

Hi David, thanks for posting. I doubt what is in the car is this part, won't know until I take it apart, but very interesting to know that my '74 parts book specifies this part number as being a 170 degree thermostat.

On a 60- 64 degree day at 70 - 80 MPG, the temperature sits at about 205.

My idea is that moving up the opening point to 200 (180Dthermostat) will inherently raise operating temperatures given constants in the balance of cooling capacity, time, velocity, engine RPM, etc.

With a big block once you get it warm, about 10 seconds, then you need all the cooling you can get, unless it is 30 degrees out side...

Ronald------


I'll repeat something I've mentioned previously: the information provided in the "parts description" column of the P&A catalogs and ESPECIALLY any parenthetical information is not always accurate. Some of the time this information represents an anachronism. In other words, information from a part that was REPLACED by the part on that particular line of the P&A catalog. The information provided for the GM #3156280 is one of these instances.

[David L.]

Re: 1966 and later BB thermostats

GM # 3156280 is definitely a 180 degree thermostat. I have sold 3 or 4 in the last 12 months and I still have a few more. My 1969 Chevrolet parts catalog (Oct. 68) and older books describe 3156280 as 180 degrees but my 1969 & 1972 Corvette parts catalog (Sept. 69 & Sept. 71) describe it as 170 degrees.
My 1970 Chevrolet parts catalogs (Sept. 69, Nov. 69, and Jan. 70) show no desription but my 1970 Chevrolet parts catalog (Oct. 70) describes it as 180 degrees.
The 170 degree description has to be an error.
GM 3156280 was replaced with GM 3033780 in April 1977 which was then replaced with 3041388 as per Chevrolet & GM Parts History. My June 1979 Corvette Parts catalog describes GM 3033780 as a 170 degree thermostat and my Nov. 1981 Corvette Parts Catalog describes GM 3041388 as a 170 degree thermostat. Are these last two thermostats really 170 degree thermostats?

[Ronald L.]

Re: 1966 and later BB thermostats

I am just going to have to pull the one that is in the car and see what it is, and then put the 180 in there to see if there is a difference - all before the weather gets bad - I know - 5 minute job, other than draining out coolant.

[Richard H.]

Re: 1966 and later BB thermostats

Can anyone out there advise as to the correct temprature rating of the thermostat for a 1966 L72 437/425hp car. I have owned my car for some 18 years and it has always had overheating problems. I have had the radiator rebuilt, I have the correct fan and a rebuilt fan clutch but still have a problem.

[Michael J.]

Re: 1966 and later BB thermostats

I have the Robertshaw Flowkooler 180 degree in my L71. But, unless your existing one is stuck closed or near closed, I doubt your overheating problem is the thermostat. Most likely if it is overheating in stop and go traffic but fine on the highway, it is the shroud seals and/or all the timing and VAC adjustments needed to keep it cooler.

[Domenic T.]

Re: 1966 and later BB thermostats

Can anyone out there advise as to the correct temperature rating of the thermostat for a 1966 L72 437/425hp car. I have owned my car for some 18 years and it has always had overheating problems. I have had the radiator rebuilt, I have the correct fan and a rebuilt fan clutch but still have a problem.

Richard,
I'm not sure but a 170 or 180 might be it, but the book would say it best.

BUT, do you have the baffling that directs the air thru the radiator?

When I installed a radiator back then there was a WARNING to make sure the baffling was in place for proper cooling.

DOM

[Duke W.]

Re: 1966 and later BB thermostats

What's your definition of overheating?

You can verify on you own the opening temperature of the OE themostat from the AMA specs that you can download from the GM Heritage site.

L72/71 tend to run hot (over 200) in low speed traffic because they have ported vacuum advance. Converting to full time vacuum advance will significantly mitigate this tendency.

It's okay to use the OE VAC - assuming it works - or a new B20/26 on L-72. L-71s must replace the OE 201 15.5" VAC with the 12" B20/26.

Current replacement fan clutches tighten at higher radiator exit temperature because they are calibrated for emission controlled engines with 195F thermostats. If yours was rebuilt, how was it set up?

...lots of archive discussions on these issues.

Duke

[John H.]

Re: 1966 and later BB thermostats

Can anyone out there advise as to the correct temprature rating of the thermostat for a 1966 L72 437/425hp car. I have owned my car for some 18 years and it has always had overheating problems. I have had the radiator rebuilt, I have the correct fan and a rebuilt fan clutch but still have a problem.

Richard -

The thermostat is unrelated to "overheating" (assuming that it's operating properly) - the link below will take you to an article that explains exactly how your Corvette cooling system works and how each component contributes to cooling performance:

http://www.lbfun.com/warehouse/tech_...em/cooling.pdf

[Clem Z.]

Re: 1966 and later BB thermostats

you need to seal the core support so the in coming air does not go around the rad. air takes the path of least resistance. one place the air goes is over top of the core support and i believe GM added a top of the core support to hood foam rubber seal on the A/C equipped corvettes. try this insert a brass cup type soft plug into the water pump to intake manifold hose to prevent the water from bypassing the rad and see if that helps. if you are worried about the water circulation till the thermostat opens drill a couple of 1/8" diameter hole in the thermostat locating flange

[Joe L.]

Re: 1966 and later BB thermostats

Can anyone out there advise as to the correct temprature rating of the thermostat for a 1966 L72 437/425hp car. I have owned my car for some 18 years and it has always had overheating problems. I have had the radiator rebuilt, I have the correct fan and a rebuilt fan clutch but still have a problem.

Richard-----


The original thermostat for your application was 180 degrees. However, as others have mentioned, I seriously doubt that the thermostat has anything to do with any sort of cooling problem.

[Richard H.]

Re: 1966 and later BB thermostats

Many thanks to all the guys that have responded to my post. Lots to think about here and I will let you know how I get on with solving the BB inferno problem in due course

Regards

Richard.

[Robert K.]

Re: 1966 and later BB thermostats

Michael,

Are these "dozen things" listen somewhere? I looked at the article the John posted and it's great re: the basics......
As noted elsewhere in this thread, there is a bunch of info. in the archives on this subject but, it hard to make out the "dozen things"?

Any chance you could post a a list.......? Your thoughts,

Thanks.....

[Ronald L.]

Re: 1966 and later BB thermostats

With the temperatures we have now, there should not be an over heat issue.

What you will find from this thread is that the temperature it starts to open is about 180 full open will be less that 200 as measured with reasonably accurate devices, not the dash gauge.