SierraTony

I just acquired a '69 350/4-Speed. It loses coolant somewhere - no water in oil; doesn't drip anywhere when parked in garage. Replacing both radiator hoses and want to replace caps but confused: one source says 15 lb. caps - most after-market caps are 16 lb. Other source says 13 lb. caps required. Which? Also, must recovery tank and radiator caps be same spec? (Eg.., both 16 lb.)

Alan 71

Hi Tony,
I'm surprised you say 2 caps.
I thought 69, 350, 4-speed cars had a aluminium radiator without a cap and an aluminium surge tank with a cap rated at 15 lbs.
Can you describe what radiator and surge tank your car has now?
Regards,
Alan

thegazman

Even though there is not antifreeze dripping from the engine, you could have a head gasket leaking into a cylinder. Look for moisture out of the exhaust and smell. You can smell even small amounts antifreeze in the exhaust.

Mike Ward

Sounds like Bubba has made a visit.

SierraTony

I'm not positive, but fairly certain my radiator is original, and aluminum. But whatever, it has a cap. As does the collector tank.

SierraTony

Forgot...surge tank is aluminum also.

A8skyhawk

Alan is correct... The original '69 350 4-speed aluminum radiator doesn't have a radiator cap... the expansion tank should have a 15 lb cap...

PeteZO6

Here is a photo of my SB '69 with the original aluminum radiator. There is a fitting on the top right side of the radaitor where the small hose connects to the surge tank. That hose snakes around under the fender in the photo so you can't see it all. It connects to the surge tank just in front of where the rad. cap mounts. You can just see the hose clamp in the photo.

SierraTony

Thanks for the foto. If that's an original Alum. rad, then mine doesn't have one. Mine has a cap where your small hose connects. However, aluminum or not, that doesn't answer my questions: do radiator and recovery caps have to be the same "poundage," and what is that "poundage" -- 13, 15 or 16 lbs? (Is the difference between 15-16 lbs significant?)

Alan 71

Hi ST,
Since your not sure just what radiator you have, I'd think you should replace the caps with the same pressure as the current caps. Can you tell what they are? They should be the same number of lbs.
Also, since you have a cap on the radiator, where is the hose that runs to the surge tank attached to the radiator? Is there a nipple right below the cap?
Could that be part of your problem?
Regards,
Alan

PeteZO6

The "poundage" is the pressure the cap can maintain in the cooling system. The higher the pressure (within reason) the higher the boiling temperature of the coolant. For example, Prestone Antifreeze mixed 50% with water has a boiling point of 265°F at 15psi, vs. 212°F for water alone at sea level pressure.

1969, and probably all other year Corvettes, came with caps rated at 15psi. If you have two caps of different "poundage", the lower rating will prevail, that is, if the system goes over 15psi, the 15psi cap will release pressure, while the other rated at 16psi will do nothing. A 16psi cap would release at a slightly higher pressure/temperature, but the car should never get that hot enough to cause a cap to release pressure, so it's kind of a moot point.

SierraTony

Thanks, All. Soon as my new lower hose arrives (2 weeks waiting), I'll put 15 lb. caps on both and take it from there. The 13 was on the radiator, the 15 on the recovery tank. Once i get under there i'll also check for water pump leaks. Glad I found this forum. This '69 is more of a challenge than my previous '85 Alfa spyder! Cheers, all.

Mashman

Just one more thing you might want to consider - do you have a vacuum cutoff switch? Mine went bad, and I started to lose coolant thru it.