Gents: Could you tell me the correct rad cap & thermostats for a '48 248 straight 8? My rad cap is 4 lbs. psi (came w/the car when I bought it last year)and I think it's too low. My engine overheated yesterday after driving about 90 mins. in 38F weather...fan belt and hoses seem fine, so I suspect the thermostats or rad cap, or both...
Thanks.

rocken bones I got a 48 248 I put a 12lb cap and a 180 ther from a 58 chevy trust me you wont find a ther by asking your year and model and it will be fine

My concern would be too much pressure for the old radiator design. Check with a rad shop, but you may find that the rad may not hold higher pressure caps. The high pressure, 12, 14 lbs. came with the tube radiator design.

Your problem will probably come from your rad not flowing, being contaminated, or from block corrosion. It may be solved with a series of flushes, back flushes etc.

Thanks for your input guys. My Buick shop manual only mentions 7 & 13 pound rad caps (for comparison) in the "Cooling System" section...no mention of a 4 lb. cap. So, a 7 lb. psi cap should be OK, no?
And yes, a rad flush needs to be done as well...

I run a 7lb cap and a 160 degree thermostat on my 263 and it never gets hot.

Rockin-Bones:
There are quite a few reasons for a straight 8 Buick to overheat and from my experience most are obvious. These include good radiator flow, coil spring in lower radiator hose, fan belt not slipping, good pressure cap (4 psi for 1948), block flushed, and ignition timing correct. Less obvious is the type and quality of the thermostat. Generally, 160 degrees should be OK, but some lower quality thermostats have a relatively small opening for the coolant flow. I have an original Buick bellows type thermostat and the opening is quite large compared to some "standard duty" thermostats I used to have. One of these has an opening for the coolant flow of about 1 inch in diameter. A "Heavy Duty" thermsotat I installed has an opening of 1 and 5/8 inch diameter. The area of the coolant opening for the larger one is over 2 and 1/2 times the area of the smaller one. Prestone markets a heavy duty thermostat called "Power Performance" and is available from Bob's Automobilia in CA. When I switched to the larger opening thermostat the temperature drop was noticeable, especially in traffic on a hot day.
Buickjoep:waving:

:thumbsup:Buick Joe might be on to some thing my radiator was full of crap my car was over heating on the hwy had it flushed out and tanks removed make sure they remove your tanks in AZ they just drop them in acid acid eats your radiator away I had it done in Calif because its illegal to use acid

[quote=Buickjoep;59467]Rockin-Bones:
There are quite a few reasons for a straight 8 Buick to overheat and from my experience most are obvious. These include good radiator flow, coil spring in lower radiator hose, fan belt not slipping, good pressure cap (4 psi for 1948)

Thanks for the reply. I have a 4lb. rad cap on mine...came with the car. However, my repair manual and all the specs I've found online say the '48 Super takes a 7 lb. cap. Bob's Automobilia doesn't even sell a 4 lb cap. So...who's right? I was thinking this may be one of the reasons it overheated...I've ordered the 7 lb cap and a new 180 thermostat from Bob's...just waiting for them to arrive. Hopefully that's all I need, but we'll find out soon enough.

Pasted from Bob's website:
Radiator Caps
1929 "Flip-lid" Style (pg.59)..RC-29.. $395.00
1937-39.................. RC-379...0 lbs........$ 7.75
1940-47.................. RC-407....7 lbs.......$ 29.50
1948-49...................RC-489...7lbs.........$29.50
1950-56.................. RC-506...7 lbs........$ 29.50
1957-69.................. RC-579...16Ibs.......$ 7.50

Rockin-bones:
You are correct about the radiator cap. The shop manual says 7 psi for the cellular type radiator. However, in an older Bob's catalog he listed 1948-49 as 4 lbs. Either way should work if the rubber seal is good and it fits properly.
Good luck.

A thermostat from a Chevy small block will fit. Any Chevy Small block, 265 - 400, also the thermostat gasket and water outlet fit, just pick the one you want.

David:
Thanks for the information. Actually, Buick offered several temperatures for straight eights, probably depending on the climate where the car got used. They were 151, 160, 170, and 180 degrees F. The thermostat, based on my understanding regulates the temperature and can prevent the system from over cooling the engine. That is, if the temperature drops below, say 160, then the thermostat begins to close thus bringing the temperature back up to the correct range. I find that the 160 works best in most areas except maybe in Florida or in very cold northern regions.

Hmmm...well, I just ordered a 180 thermostat from Bob's....I hope I made the right choice! I live in Vancouver....it gets down to around 0C (32F) in the winter and up to 30C in the summer...averages around 15-20C most of the year, I guess.