Hi All,
Wondering if I can get some help please. The temperature light on my 1969 350 started coming on recently. I don’t have a gauge. So I did the following:
1. Checked hoses,
2. Put in a new 160 degree thermostat
3. Checked water pump is pumping
4. Clutch fan doesn’t spin freely and only about an 1/6 (maybe up to a 1/4) of a turn with a harsh flick
5. Pulled out checked cleaned, radiator
6. The timing has been done. I don’t think it’s a problem, but could be I suppose.
7. The carby seems to be bolted fine.

None of this helped; the light would still come on even on a cool day. (ie, 70 to 80 degrees F). Typically if idling at traffic lights or intermittently when driving. So I then replaced the sender. I put in a Wells TU46 - listed for heaps of GM cars including first gen Camero, but not specifically for firebird (?) I’m not sure.

Today I ran the car a few miles. (about 70 degrees F outside today) Then let it idle for about 30 minutes in my driveway. For the first time the warning light did not come on.... but! When I checked under the hood, it seemed to be cooking! I turned off the engine and could hear it all bubbling and gurgling. Sounded like it was boiling. The top radiator hose was quite firm too. There was no leaking or steam.

I put my infra-red heat gun on the hoses and they measured about 240 degrees F, which is actually cool, right? So may be it wasn’t boiling ? But it sounded like it. BTW, the car is completely standard.

So I’m hoping someone can please help me, cos I don’t know what to do next....other than to go and buy a new Mustang and have a beer.

Nice,

This issue has been flogged to death on this forum lol. Try searching with "over heating" and look at some old posts.

You can add an aftermarket temp gauge to tell you what's really happening. If it really is overheating (temp over 220F or so), there could be many causes and all of them will require some work. The radiator could be clogged, the water passages in your engine could be clogged, or your water pump might be rotted out or not assembled correctly. Not sure of the condition of you car and whether any of these are likely or not. My friend's 68 cougar drove him nuts with overheating and he finally took apart the water pump and the impeller was rusted away and not functioning. The 455 I procured for my goat the water pump was missing the rubber sleeves. Somehow it still functioned enough. I could see the missing sleeve when I removed the upper hose.

The bubbling and gurgling after shutdown is no big deal. The heads are hot and the water is just sitting in them and not circulating.

Go buy a mustang and have a beer. Then get back to work on the bird

Think I’ve been through forums on this, but maybe I missed something. Timing, fan, water pump are all good, I confess I haven’t looked in the engine jacket itself, and I haven’t added a gauge.
Thanks for the ideas.

Try useing your temp gun on the front of the radiator unless you have ac then you need to do this on the back of radiator
car needs to be at operating temp
Your looking for hot and cold spots in the core so your going to have to move it around top to bottom side to side
big temperature changes mean the radiator has some issues
Blockages not flowing right thru the core
You can also use temp gun to check upper and lower hose temp
Lower hose should be cooler than top

Some times a blown head gasket will put air in the water jacket and you can hear it bubbling out after the engine is shut of and cooling. You can pressure test the cooling system to see if it leaks the other way. Pulling the plugs and checking if one looks steam cleaned is another test as is a cylinder pressure test, checking for watery foam under the oil filler cap, looking for foaming or air bubbles in rad when running and checking for coolant under the head or around the intake manifold.

You said the hoses measured about 240* - top & bottom? Sounds hot to me. What did the temperature measure right on the intake beside the thermostat housing? Are you sure that you installed the new thermostat correctly, pointing up? What was the condition of the coolant you removed, clean, dirty, oily, foamy?

When you checked the hose temps, was the car running or was it just shut down?

Running, the upper hose should be about the temperature of the thermostat opening temp, and the 160 degree is too cool in my opinion, and the lower hose should be about 30-40 cooler going back into the motor.

Once that 160 Opens up, it's never going to close again until you shut the car off and let it cool down.

If you have 240 at the upper and the lower hose running at idle, you have either flow issue or a restriction somewhere, possibly in the water jacket.

The idiot lights come on for temp in our cars around 240-243 degrees if I remember correctly.

I understood the "HOT LIGHT" to come on at 246*...but I'm not positive.

Change your thermostat to 180-185*.

240* is HOT!

Is this HEI or points

I changed to HEI and timing was a lot different.
I am actually a couple degrees ATDC
now that may be incorrect setting but it runs very well and stopped over heating.

Thanks everyone for the advice and replies. To answer these in summary,

1. To ”Mickey”, I checked out the radiator again. It does still run a little cooler toward the bottom than the top, but it should be ok as it was overhauled and retested just before Christmas. Heat naturally rises of course. Maybe 5-10 degrees is a reasonable difference top to bottom?

2. In hindsight, letting the car idle for 30 minutes probably wasn’t one of my smartest moments. Easy to forget this car is almost as old as me Yes 240 degrees was hot, but the few times I’ve driven it since then, and on much hotter summer days, the top hose temperature hasn’t exceeded about 220 degrees. The bottom hose is typically about 190 degrees immediately after the drive. So this is all due to the added air flow while driving I guess.

3. To “Bluebird 428”, “Cal H” and “Dr Drivability” thanks for the thoughts; the head gasket is fine though. The thermostat is in correctly etc,...The new sender hasn’t tripped the warning light either. I wrote to Wells about the TU46 sender. They said it activates at 263 +/- 10 degrees. This seems pretty hot to me, as I’m sure you guys would agree, so maybe I still need to look for a lower temperature sender. But I don’t have a factory spec on this, so I’m not sure.

Finally, to “Bob S” I haven’t had a chance to put a gauge in yet, but will do this in the next few weeks as a precaution. But for now I’m concluding the operating temperature is ok and that the old sender unit was tripping the warning light below the appropriate temperature effectively giving a false positive.

That’s normal since water flows from upper hose to lower hose
might even want to see bigger temp change from top to bottom
All in all as long as it doesn’t overheat
Glad you figured it out
Now go drive it and have fun

Still sounds like it's running hot,.mine stays right around 180-190, make [censored] sure that the radiator shroud is there and that the fan is half in half out, everyone I know that removed their radiator shroud on a Pontiac because it looks cool started having over heating problems, still if you're motor was over heating you'd hear it when you shut it off, and it should be puking out the overflow.

I also use Water Wetter, I don't even run hot on 100 degree days