69 z28 302 running hot on hwy

[subyman99]

Hi, i just took my 69 z out for a ride tonight, was gonna hit up a cruise that was about 60 miles from town, ive never really got the z out to stretch her legs but has always been great around town. Soon as i hit the hwy the temp climbed to 205 degrees at around 60 mph, the faster i went the higher the temp. Everything is original and stock on the car. Any ideas? the engine has been rebuilt, with all stock oem parts. Thanks

Matt

[Salvatore]

sure it was a true 205 degrees? Did it smell, boil over, lose some power etc? NO water pump leaks, lose fan belt, bad clutch fan? Hows the radiator situation? Try some of that water wetter solution. 180 is OK in my book.

[subyman99]

ive got a aftermarket mechanical gauge, since my factory one was reading hot, my aftermarket gauge was showing all of 205, no boiling over, exept for the a few drips of coolant from overflow. I want to see 180... Imo its running to hot

[1969z280]

The fan clutch sounds like a likely culprit. Once the engine is hot, turn it off and if the fan still spins, it's the clutch.

[Salvatore]

process of elimination I guess Matt. Could be the fan clutch but if it was running cool around town it would probably have acted up there also. Hows your rad. cap?

[BARRY]

how warm out side is when this happened

[subyman99]

ive tried 2 rc15 caps and one aftermarket... no change, tried a diff thermostat, i even pulled the engine to replace with an offroad cam, and fix an oil leak, i pulled the heads off and put new headgaskets in it at that time, i didnt like the way the factory shim gaskets fit.

[subyman99]

its maybe 70-80 degrees outside, the engine was still very warm from the trip, i backed it out in the driveway, let it idle till it got just shy of 200 degrees, shut it off and i can move the fan pretty easily, it was pulling some air through pretty good when it was idling, bad fan??
Thanks!!

Matt

[Salvatore]

mine moves fairly easy also. maybe try a flex fan if you have one. Off the road cam may make it run a little hotter also. 4.10 gears? Any lead in your gas? Radiator flowing correctly?

[subyman99]

91 octane, no lead. 3,73 gears. Radiator flows nice. I'm stumped!!

[TDW]

Timing a little retarded? Running a little on the lean side? What jets are in it? Vacuum advance working?

[Salvatore]

If it is not boiling over, running erratic, pinging etc.leave it go and put some more miles on it. I would try to find some better gas if I were you or at least a lead additive. I think you can do better than 91 octane and then do what Tony suggests. With the off road cam you are making some pretty good HP.

[MosportGreen66]

Check the timing. I also suggest a Milodon 160 degree thermostat. The thing is costly ($15 from Jegs) but the motor will run cooler. I also suggest checking the fan clutch. Like Ed said, have someone shut off the car with you standing in view of the fan. If you see it spinning with ease after the car is shut off, then the clutch needs to be rebuilt or replaced.

[subyman99]

Ill check the fan tonight, ever since i got the 69 running ive been disapointed on the power this car made, it seems like there isnt much there, but then again every thing else i own is a big block. I had a 68 z28 that was stock, exept it had lower compression pistons for todays pump gas, that little car really went.
thanks again for the help!!

Matt

[Mr70]

That's not unusual,especially with a bone stock 302 in front of a 3:73 @ 60mph.
Your car was intended to go quick off the line,not go for miles & miles non stop @ 60-70mph on the interstate for long periods of time,like the family station wagon.
Your reading head temp.not block temp.,so it's not as severe as you think.
Head temp.is always hotter then block and not a true internal overall reading.
Trying driving @ full speed with the heater blower motor fan on high,and see if that helps dissipate it to a lower temp.
Many other good suggestions have been listed that might help lower it.
I'm pushing a 4:10 behind my dead stock smog L-78 Chevelle,and found installing a 160° thermo & flushing the entire cooling system lowered it severely.

[subyman99]

I'm reading head temp on all my big blocks in my other camaros, none run as hot as this car. I'm going to try a few things this weekend. Thanks guys

[Hemicolt]

As long as there is nothing wrong with the tune, in the engine or bad clutch on the fan, you should look at these guide lines.
If your car runs hot at low speed or idle, but runs cool driving at highway speeds, it should be a lack of air flow as the problem.
Running cool at idle or low speed but running hot at highway speeds will suggest that the coolant is running through the system to quick and it doesn't have enough time to cool. Several things can be looked at to fix this problem. Pulley sizes can be one as the water pump may be spinning to fast. Also, installing a 165 degree stat. doesn't help with this problem. If your car runs at 185, this will mean a 165 stat. will be wide open at all times and the system will have less restriction. Using a higher temp stat. will insure that the stat. is not open all the way and will provide restriction which means the water slows down at highway speeds. Does your car have a cowl induction hood? If so, is the scoop sealed off from the engine compartment?

[Salvatore]

Matt, that car needs a rear especially with that cam. That cam probably slowed that Z up some. I run 56's with a wide ratio Muncie. My motor is stock and that really woke it up. 200 degrees like Mr. 70 said is not a killer temp IMO either.

[67 Nova Boy]

I was running a clutch fan when I fired my 302 up and it hit 260 in 10 minutes. Had to shut off {During break in of motor} and installed a flex fan and right down to 180 deg. Ran there for 10 years with 180 stat. I ran 4:11 and after 3,800 rpm the car would run at 200 deg doing 70 mph. Drop down to 3,300 to 3,500 and back at 180. Never mattered the outside temp...it still ran 180. Drove to Super Chevy last year when it was 90 and humid out and ran 180. My temp sender is in my passenger head so it might be cooler yet?

I run a wild cam {560/560 294 Soild} and runs cool. Try a flex fan as Sam says!! He knows this stuff!!!

Dave
67 Nova Boy

[subyman99]

just got back from a drive, i put in a radiator i had from a 68 big block, along with a deeper fan shroud i had laying around. works great. runs 175-180 on the hwy. Either the stock radiator isnt flowing good, or my fan isnt deep enough into the shroud? It sat maybe a 1/4 of the way in the shroud. Thanks guys!!

Matt