Stock 350 getting hot, but only on the highway with AC on

[Old60Driver]

Okay, this makes no sense to me. I can cruise around all day in this heat, city or highway, no problem. Temp gauge is 180° or so consistently. I can turn on the A/C and cruise around city driving, no problem.

Here's the issue. When I hit the highway and turn on the A/C, the temp climbs to 208-210.

Thinking my lower hose might be sucking closed.

Thoughts y'all?

 

[75gmck25]

I worked through a similar issue with my K25 and the final fix was a new aluminum radiator. Due to the 4.10 gears and higher rpm, mine was apparently generating a lot more heat at 65-70 mph. It never overheated, but did run hotter on the highway. It really liked about 40-45 mph a lot better.

Based on my AFR gauge my Quadrajet also runs quite lean at cruise, so that may have been affecting the engine temp.

 

[squaredeal91]

When it happens pull over fast and look at the lower hose. I like your theory on that

 

[1STLS1]

My bet is the radiator is plugged up or has debris between the condenser and radiator blocking air flow.
Is the shroud in place and any other ducting between the rad and condenser?
Going down the road at 2-2500 rpm requires higher flow thought the radiator to get rid of the heat from the engine, adding the heat from the condenser just takes takes it over the top.
Copper brass radiators end up getting corrosion at the end of the tubes that can restrict flow, a competent radiator shop can "rod" the radiator by removing a side tank and running metal strips through each core tube then resolder the tank on to restore coolant flow.

 

[Matt69olds]

Unless it gets hotter, 210 is no big deal.

Make sure all the shrouds and baffles are in place. Make sure the shroud fits snug to the radiator. Make sure any air that enters the grill has to pass thru the radiator on the way out. Make sure there is nothing trapped between the condenser and the radiator. Leaves, pine needles, papers, etc somehow find their way in there. Carefully blow out the radiator and condenser, you will be amazed at the amount of bugs and debris gets caught that you can’t see.

 

[fast 99]

If it has a fan clutch does it work? Fan blades should stick out the rear of the shroud about 1/2 - 1".

 

[Old60Driver]

Thanks for all the tips y'all. Travelling this week, so I'll be taking a look over this coming weekend.

It's crazy though. I can run at 65 mph all day on the highway. Only when I turn the AC on does it heat up.

Gonna check lower hose, and air flow blockages. See if I can see something obvious. I'll let y'all know how it pans out!

 

[Rusty Nail]

Uhhhh ...

Uhhhhh....

Air in the cooling system...back to CAVITATION. Is it full of water or coolant ?
Air in the cooling system oh wait! I got it.
Fan clutch not unlocking. Bingo! That's it. Bad fan clutch.

 

[Rusty Nail]

Think about it. It should unlock at highway speeds. It doesnt unlock light to light and there is no problem. Doesn't unlock on the road..that's it.
Bet if you look at it hard enough you will find signs of the oil leaked out.
Cooler ambient temps? Non problem.

Take pix ffs and post them here pliz.

**I only install Hayden brand fan clutches but only because they are the best in my experiences.

Thermal

www.haydenauto.com

Don't thank me, buy a bumper sticker from the GMSB.com online store and post the pix, you'll be alright.

 

[Rusty Nail]

1/2 inch, or 13mm combination wrench.

 

[Rusty Nail]

In addition:

The lower hose is intended to have a spring in it - to keep it from sucking closed. A guy or girl (you) should always re-install that spring in a new hose if necessary, that is why they are there OE. The lower hose "sucking closed" is a problem that should never be a possibility.

I thought I would add that and very recently I have turned off of editing threads and pledge to spend more time in composition to provide a better end user experience from this website. Frankly, you all deserve better of me and it is possible to provide it for you. I really want to help but have enjoyed poking fun at noobs occasionally . Last weekend I reached the breaking point after TEN YEARS in this site i've had plenty of lulz and I'm not about to apologize (lol) but I will do better as well all move forward. Thanks to the mods that have allowed me to be a jackass sometimes because I actually add something positive occasionally , I guess. I don't know but this IS the WORLD WIDE WEB.

Is no matter because that's behind us now.

 

[75gmck25]

In my experience lower hoses I’ve purchased no longer have a spring inside. The molded design is supposed to prevent collapse.

 

[Snoots]

If you hear a loud roar, and it ain't your exhaust, at highway speeds then it's the fan clutch.

 

[Buck69]

You should also check your belt condition and tension. A bit of a long shot, but an oily or glazed belt will not always screech when it is slipping. The extra load at higher rpm may just be enough to make the difference.

 

[Craig 85]

Do you have a 16 LBS radiator cap? Just ran into this with a friend that put A/C on his '62 Belair. No over heating issues until the A/C was installed/used. Previously he had a 13 LBS cap which was standard for a non-A/C car.

With the new cap, no overheating.