Young mechanic learns something new. Problem fixed, now a new question.

[lvin4jc]

My '63 has been running warm, very warm since the weather turned nice outside. It's been anywhere from 3/4 to all the way up the stock gauge. But when it got all the way up if I took it easy on the old girl the temp comes back down to the 3/4 mark. I thought that if a thermostat was bad the temp would get hotter and hotter until the engine eventually blew up. So i've been spending my afternoons flushing out the radiator, cleaning it, flushing it out again several times etc. I finally decided to pull the thermostat and boil it, sure enough the 160 degree thermostat never opened even after the water was boiling. I put it together without a stat and the truck runs cool as a cucumber, between the quarter and half marks on the stock gauge. Problem fixed.

Now I have a new question. I have been running at 40-45mph because the truck would warm up too fast at higher speeds. I had only had the truck up to about 55 mph so far and that was just for a few seconds. Now that it runs cool it could potentially run a little faster. I ran it up to 70 mph today just there and right back down just to see how it did. It did it fine but i'm quite sure the truck doesn't want to do that for any length of time. And I don't need it to either. I drive backroads and if I could consistently drive 50 mph or even 55 mph for 15 minutes at a time that would be great. At 50 MPH the truck is turning 2,500 RPM. This is a 305 V6 truck. So I guess my question is what was the speed limit in 1963 and what speed is the truck designed to drive at for long periods of time?

- Joe -

[rideblue00]

Well, speed limits used to be 55 around the time these trucks were made. I dont think occasional 60 to 70 spurts are a problem. Freeway driving at sustained high rpms are not reccomended for the V6 im sure. I would say 55 would be my limit for the freeway.

[jocko]

speed doesn't matter, only rpm. So whatever the answer, it could be solved with an overdrive transmission or lower (numerically) rear gears, or both. I'd agree that the 305 probably wasn't really made for high revs. It is annoying to be at that high of an rpm at higher speeds - but there are ways to make it work!

[MusicMan70]

Hey Joe, good to hear you solved it. Way to work it out! You should go back and put a new thermostat in when time permits. The maximum rpm for these engines is around 3400rpm's. 50-55 or even 60 mph should not be problem; just don't overrev-it.

Here is the link to the 6066 GMC site with more info on these unique engines in case you hadn't seen it before.

How about some pic's!

http://www.6066gmcguy.org/

[lvin4jc]

Thanks guys, sounds like she'll handle my backroads cruising with no problems and that's all I need.

I have to tell you, i'm on a couple of other forums and a lot of guys have told me what a boat anchor this 305 is but i'm loving it. I've always like low end torque engines and this thing is a beast when it comes to that. My old DD (the '63 has been my DD for a month now and will be at least through the summer) is a 1989 F350 with a 460 under the hood and this old 305 feels just as torquey at low speeds as that big block V8. Plus I think i'm getting a little better mpg's to boot!

[Corts60]

A lot of people trash the V-6's because they don't produce massive amounts of power and they can't rev high because of their weight and 60 degree design. But they are the smoothest running, most reliable 40+ year old engine I have ever owned. With the exception of over-revving, they are basically indestructible. I'm glad you are hanging on to it!