Over heating question

[hooverfish]

Drove 20 miles to the local cruise last night with the a/c running. Temp gauge normal, running a fairly new 160 thermostat (72 350 automatic). I opened the hood upon arrival and everything under the hood was hot. The hood release latch was even hot, as were the inner fenders, radiator support, etc.

Read one thread that said you could bleed air out of the cooling system, can someone tell me how to do that ??

Noticed that my fan blade will turn easily with the engine not running. Is that normal. Bad fan clutch?

Didn't check the lower radiator hose while it was hot, will maybe do that today. Lower hose collapsing?

Puzzled that my temp gauge is normal but seems hotter than a firecracker under the hood. Seems to run fine but now afraid to drive it much.

Any help appreciated.

[B. W.]

your 350 will "self bleed" if you've driven any distance at all the cooling system is bled

if the fan clutch is turning without any resistance when the engine is cold, replace it. it should have moderate resistance when turned by hand (engine off - do I really need to say this!?)

if the lower hose was collapsing you would have seen higher temperatures at the gauge so it's probably not the problem

what was the ambient temp when you drove it? the radiator is getting rid of a lot of heat, everything under the hood will heat up in high ambient temps (I know you know this, just saying it anyway)

I would confirm the temp gauge is reading correctly using a laser temp gun. you can "shoot" the thermostat housing for an accurate temp. it's actually kinda cool (pun intended) you can "see" the thermostat open & close if you hold the gun steady (it's that accurate!)

if the radiator isn't boiling over & the temp gauge is accurate, i would just change the clutch

Bobby

[davepl]

I would invest in a cheap IR thermal gun to sanity check what you're seeing at the gauge. If the thermostat housing is 190 when the gauge is normal, that's fine. But if the temp is 230 and the gauge is reading normal, you need to know that. Right now you can only assume the gauge is right. Might as well know for sure, and there's a million other uses for the temp guns, a good investment.

[Stocker]

Originally Posted by hooverfish

Noticed that my fan blade will turn easily with the engine not running. Is that normal. Bad fan clutch?

It's hard to describe in print how easily or how hard it is to turn the fan. You should be able to rotate it easily, but there should be resistance -- like it's mired in molasses, if that helps. If you can spin it quickly, or if it spins even a little after you take your hand off of it, the clutch is bad.

[davepl]

I'd say you shouldn't be able to get more than about half a rotation after you let go of the fan. If you can spin it hard by hand and it goes all the way around, that'd be too much.

That's a real ballpark answer, and it's a big ballpark, but a full spin would be over the wall, as it were...

[Stocker]

Your experiences may have been a bit different than mine..... I have never had a fan spin freely, even a little, after I let go of it. Just my 2 cents

[FlounderGDI]

I've been struggling with some over heating problems lately myself. My truck has a Pontiac 400 instead of a SBC 350 though. I was running 220 when driving around town.

I bought an IR thermometer to see what temp I was running because I didn't trust the aftermarket gauge I was using.

I replaced my 180 degree thermostat with a new 180 degree thermostat.

I installed a fan shroud and clutch fan (mine didn't have one and I had to hack it to pieces to get it to fit the Pontiac accessories.

I checked and reset my timing.

I tuned my carb to not run a lean Air/Fuel mixture.

Now my truck doesn't climb over 200 on the gauge and IR thermometer even when idling in the driveway for 30-40 mins.

[hooverfish]

'Thank you' to each of you who have replied, good input from all.

I replaced the fan clutch today, $30 and an hour labor, but it didn't help.

I'm buying a cheap IR thermal gun off ebay as was suggested.

Will post results in a few days . Thanks again.

[JCD]

Try a higher temperature thermostat.
Strange as it seems..
The higher the thermostat, the cooler your engine will run.

J.

[garyd1961]

Originally Posted by JCD

Try a higher temperature thermostat.
Strange as it seems..
The higher the thermostat, the cooler your engine will run.

J.

Never heard this before.
I found that you need water circulating through the heater core for these motors to cool properly. I have a leak in my heater core so I plugged the ports off when I installed my new crate motor. The temp would be fine for 10 or 15 miles then it would jump to the hot side and back to normal. I installed a by-pass hose where the heater hoses should be and it runs constant on the low side of normal now.
I have a new heater core and will be installing it asap.

[special-K]

Mine seems a bit hotter than it should be, too. The air filter housing gets too hot to handle. My circuit board is fried and I need to get to that, but I am sure it is hotter than usual. I have a 180 deg t-stat. It's new and I tested the old one which is still fine. I had an issue a few years ago that resulted in new fan clutch, water pump, and it ended up being poor flow through the radiator. I took another one (4 core) to the radiator shop for the royal treatment. It ran nice and cool after that. Now, with fresh heads, a freshly rebuilt carb, tune up, fresh hoses, and plug wires after it gets up to temp and I shut it off, after a few minutes it just cranks it's butt off without a kick at all. Let it cool down and runs like a top. I suspect ethanol poisoning since it sat since May '15 till a couple weeks ago, combined with extra heat. But why so warm? I need to go through it all and try other timing/carb adjustment. Maybe a weak diaphram in the fuel pump not pumping well once warm. i already replaced the ign module, and it starts on starter fluid, so not the coil. I need to put some time into it son. I hoped to get a clue to it's running hot issue here. It isn't over heating, either. I loaded it up with a loaded trailer and went 75 miles with two mountains to cross and it did fine. Just don't shut it down unless you have 20-30 minutes to spare.

[special-K]

The clutch and even fan only come into play, for cooling, when air flow from traveling is low. Such as sitting, stop and go, or moving steadily at a very low speed. The purpose of the clutch is to "disengage" the fan when not needed vs constant fan. It's about less drag on the engine for power and economy.

[Stocker]

^^ Under 'normal' circumstances, yes..... but a fan clutch will engage whenever high temps call for it, even with reasonably good airflow. Example: going uphill, esp. with a heavy load. You might be doing 45-50 mph but the engine temps rise and the fan engages. I've had it happen many times with my pickup as well as several trucks at work. Hot weather and a long 6% plus grade will do that. Come to think of it, I've also had it happen on flat ground at highway speed in very hot weather. No fun at all in a truck with no A/C.

[special-K]

Originally Posted by Stocker

^^ Under 'normal' circumstances, yes..... but a fan clutch will engage whenever high temps call for it, even with reasonably good airflow. Example: going uphill, esp. with a heavy load. You might be doing 45-50 mph but the engine temps rise and the fan engages. I've had it happen many times with my pickup as well as several trucks at work. Hot weather and a long 6% plus grade will do that. Come to think of it, I've also had it happen on flat ground at highway speed in very hot weather. No fun at all in a truck with no A/C.

That's true, and when I had my "temp climb" issue a few years ago it was running harder up a gradual grade on the hiway. I'd slow it down a bit and it was fine. I suspected the fan clutch and changed that first, along with replacing t-stat. Problem persisted, went ahead with a ump and took radiator to my local wizard. Bottom half was crudded up and he didn't feel it would survive a rodding. I brought him another and he blew it apart, did his magic, reassembled, and pressure tested. He said "We're not out of the woods yet. It could start leaking once heated up". It was fine.

I know my cooling system is fine and when the heads and manifold were off the engine was clean as a whistle. New heads are 64cc 1.94" where old heads were stock '72 truck. Mine's probably the higher compression (maybe slight heat increase), timing, carb adjustment, and maybe even plug heat range(?) combined with possibly a weak fuel pump or ethanol issues. It just cranks when warm till cools down and also starves when warm when I hit it. I didn't have time to get into it this weekend. Meanwhile I'm putting a wood base gasket under the carb and checking filter. I want to pull the seat and check the sock in the tank, too, maybe pull tank and flush. I feel it's a little heat and a little fuel delivery. It's not starting as eagerly as at first when cold either, so likely my friend ethanol mud paying me (and my fresh carb) a visit

EDIT: I also drilled an 1/8" hole in the thermostat

[GASoline71]

When I read "overheating" I immediately think of a vehicle sitting on the side of the road puking coolant out of it. If that's not the case, then a rig is just running a little hotter than normal. But...

If you're running around 200 degrees, I would say that's close to normal operating temp as the thermostat does it's job. I agree that running a 160 degree thermostat won't help. Heck even newer rigs run at operating temps of 200 to 215 degrees.

Also depending on what the heat index is where you live, is probably not helping matters.

Gary

[72freak]

When we have them run warm or hot, the first thing we do is check the temp with a laser gauge, check and set the timing, put thermostat in a pot of water on the stove, throw a replacement radiator in it off the shelf and check the water flow to make sure the water pump is working.

On the junk we bring home most of the times its timing or a "clogged up" radiator.

[davepl]

One day I'm going to write a really big and long manifesto out in my Unabomber-style shack on two things:

"The Myth of Slowing Coolant Down - Why Faster is Better"

and

"The Sin of Connecting Your Vacuum Advance to Manifold Vacuum"

Both of these evil lies must be stopped. But today is not the day. For now, just know that "slowing coolant down so it has time to cool in the radiator" is not a real thing.

One day, many decades ago, a drag racer fixed water pump cavitation by installing a restrictor plate in an engine that lacked a thermostat and somehow the legend took hold. But that was pump cavitation, something completely separate. You want to pump it as fast as you can without cavitation.

Thermostats are there to set the low point - then they open. Higher thermostats will not cool better, cooler thermostats will not keep an engine cooler if the fan/rad package can't hold the temp constant at or below the thermostat open point.

[MiraclePieCo]

Originally Posted by davepl

One day I'm going to write a really big and long manifesto out in my Unabomber-style shack on two things:

"The Myth of Slowing Coolant Down - Why Faster is Better"

For now, just know that "slowing coolant down so it has time to cool in the radiator" is not a real thing.

Ha ha, the illogic of that persists with the tenacity of old wives tales and Facebook-perpetuated conspiracy theories! If slowing the coolant through the radiator is a good thing, entirely stopping it must be great - remove your water pump belt entirely!

[special-K]

I understand how the system works. The system is all about circulation through the radiator for cooling. It's that simple. No circulation/no cooling. People only replace a thermostat that sticks open to get heat, they replace one stuck shut to get cooling