Overheats on Freeway
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Z-man,
My father bought the car new in 68 and I started driving it in 75. It never ran over 190 on the freeway even during hot Maryland summers where I lived as a teenager. So I think something is wrong. But from the responses, it seem this is normal for many big block cars.
I replaced the fan clutch a while ago. When the engine gets hot, you can hear it turn on. Should it not engage after a certain RPM? I could try disabling or removing the fan and make a freeway run on Hwy 280 near my house. I can probably remove the 4 bolts from the fan, remove the fan/clutch and replace the bolts so the sheave will turn the waterpump.
I'll post after I've tried it.
TT
My father bought the car new in 68 and I started driving it in 75. It never ran over 190 on the freeway even during hot Maryland summers where I lived as a teenager. So I think something is wrong. But from the responses, it seem this is normal for many big block cars.
I replaced the fan clutch a while ago. When the engine gets hot, you can hear it turn on. Should it not engage after a certain RPM? I could try disabling or removing the fan and make a freeway run on Hwy 280 near my house. I can probably remove the 4 bolts from the fan, remove the fan/clutch and replace the bolts so the sheave will turn the waterpump.
I'll post after I've tried it.
TT
Instructor
Joined: Nov 2001
Posts: 175
Likes: 0
From: St Louis MO
Check to make sure that your lower radiator hose is not sucking closed when you are turning the higher rpms at highway speeds. I am not sure about your car but mine has a spring in it to keep that from happening. I have seen 350's collapse that hose and restrict flow when a cheap hose without the spring is installed.
Burning Brakes
Joined: Jan 2004
Posts: 769
Likes: 0
From: Ft. Lauderdale Fl
I just skiped over alot of post. I don't know if this is a repeat or not.. I installed a thin electric fan in front of the A/C condenser and set it as a pusher fan along with the stock clutch fan. This fan also runs constantly. My temp goes up to 200 degree's in traffic and 165 degree's on the highway 
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Yogi78,
Since I couldn't possibly explain all the little details about my car with out writing a novel, your suggestion of a collapsing hose seems most likely. The faster I go the worse it gets. I did replace the lower hose during the rebuild. I'm sure it had a spring in it but that doesn't mean it won't collapse if it is a cheapie. I don't remember if I got it from one of the mail order suppliers or could have been Kragen or similar.
I'll get it hot, rev it to 4 or 5k and visually check it.
Thanks,
TT
Since I couldn't possibly explain all the little details about my car with out writing a novel, your suggestion of a collapsing hose seems most likely. The faster I go the worse it gets. I did replace the lower hose during the rebuild. I'm sure it had a spring in it but that doesn't mean it won't collapse if it is a cheapie. I don't remember if I got it from one of the mail order suppliers or could have been Kragen or similar.
I'll get it hot, rev it to 4 or 5k and visually check it.
Thanks,
TT
It wasn't a collapsing lower hose. I'll have to wait until next weekend to try other fixes. 
Instructor
Joined: Nov 2001
Posts: 175
Likes: 0
From: St Louis MO
I would try running without the thermostat to see if it still runs hot, especially if you are using a non-AC/Delco thermostat. I have had bad luck with the chain store thermostats and only use OEM now. Also, make sure you don't have any air left in the cooling system.
Racer
Joined: Feb 2005
Posts: 282
Likes: 0
From: chicago south burbs IL
ok Im haveing the same problem i replaced every thing in my cooling system rad, support,seals,hoses ,waterpump ,thermostat (x2) and went to dual 12" electric fans(2800cfmand yes the going the right direction). Im fine in town but I hit the highway and temp jupms up to 220+ so im thinking im running lean but..... how can i check and or adjust the carb to run richer off idel. thanks 
