Buick Straight-8 Overheating: Coolant Bypass Valve
There is a particular type of overheating which takes place
in pre-war straight-8 Buicks that this solution addresses. The problem is
difficult to diagnose unless you're intimate with the intent and operation of
the by-pass valve. Please note that the procedure and approach described here
is for large series engine in a 1937 Century. The smaller series engine, used
in Specials, also uses this type of coolant by-pass valve and the procedure
outlined here is applicable. If you are working on a small series engine you
may observe some minor differences in the images of the casting and valve from
those pictured here.
- The symptom is that the Buick gradually overheats
when being run at high RPM (like an extended drive on the highway). For
normal city-type driving, or lower speed continuous driving no overheating
takes place.
- When diagnosing, on the highway when you begin to
observe increasing temperature, reducing your speed quickly mitigates the
problem, with the operating temperature returning to the thermostat set
point and remaining constant thereafter as long as the lower speed is
maintained. Increasing your speed again, you again observe gradually
increasing engine temperature. The temperature will continue to climb as
long as the higher speed is maintained.
The following three files which make up this documentation
are:
- Logan_ByPass_Procedure.docx: This is the article
Harry Logan provided from a club in California. It exactly described the
symptoms I encountered, and the fix resolved them.
- Bypass_Original_Bottom.jpg: This is the original
by-pass valve, in place in my Century. It appeared to be working properly,
although I had the overheating problem as described. My educated guess is
that the spring was too weak to prevent it from opening at high RPM.
- Bypass_Mod_Bottom_Inserted.jpg: This is the
completed modification. I used a 1/4" hole in the freeze plug. This fix
has fully resolved my overheating issue.
This casting which carries the by-pass valve was changed in
the later versions of the Straight-8 (I examined one from another member's 1948
Roadmaster). The bypass valve was removed, and the casting is solid with a
small opening. The factory approach to solving this problem is essentially
identical to the fix described in the article.
An alternate cause of overheating:
When I first completed my restoration, I had an issue that the Buick would
overheat after about 5 minutes of operation, only for the first use of the day.
I would stop, shut it off, then if listening carefully would suddenly hear a
rush of steam and hot water into the radiator. I determined that I had
initially installed the thermostat upside down, so it was exposed to the cooler
water in the radiator and did not open. Only after stopping was enough heat
conducted to the thermostat to open it up. Once the thermostat opened, no more
overheating for the duration of that day.
Please feel free to contact me at your convenience should you have any further
questions or concerns.
