Running hot at idle but not at speed

[jwoodywild]

Hi guys ,
Odd thing. I had my 76 dialed in on temp for awhile. Then one day ina parking lot I heard a noise, saw a small puff of smoke but nothing more. Over the coming days I noted at idle or stopped at a red light temp goes up to 250 which never happened in all the years I’ve had it. But once I get going to 25 or more it goes down to sub 210. In fact this weekend I drove it 35 highway miles all under 200.

I’m not mechanical at all. What’s up?

Btw - it’s really driving great even with the wild temps.

 

[73azbronco]

clutch fan?

Smoke from where?

Time to do a basic tune up. Verify all numbers, timing, vacuum, cylinder pressures, etc.

All those good, when was last time coolant was flushed? Filled?

 

[69 Red Bronco]

Increasing temps at idle usually indicate an airflow issue over the radiator. Once the vehicle is at speed it has airflow again dropping the coolant temperatures.

The puff of smoke is interesting and im not certain how that would tie into an over heating at idle issue. Could be running lean at idle and its the carb that got messed up when it popped? Im just throwing an idea out there.

 

[blubuckaroo]

Could the puff have been a coolant leak?
Did you check the coolant level after the "puff of smoke?"

 

[jckkys]

Puff of smoke? From the tail pipe or under the hood? White smoke or black smoke? Burned oil produces blue smoke. What does the smoke smell like? What engine cooling fan? Is there a shroud? No or reduced air flow through the radiator is the most likely cause of over heating while the vehicle is stationary. Hot air that has passed through the radiator may be pulled through again. Not as common, but does happen in stalled traffic.

 

[blubuckaroo]

Hi guys ,
Odd thing. I had my 76 dialed in on temp for awhile. Then one day ina parking lot I heard a noise, saw a small puff of smoke but nothing more.

I had that happen once. A noise, then a puff of steam...

 

[SHX669]

What type of radiator cap are you using one with a release lever?
What # rating is your cap , how old is it , is it in good condition?
Have you checked your temp sending unit to verify it's sending correct resistance readings?

 

[EricLar80]

Take the distributor cap off, and move the rotor bank and forth to make sure the distributor gear meshes well with the cam gear. I had a cam gear wear out on me one time, and it causes the timing to get messed up. You could have broken a tooth off the gear even. In my case, it retarded my timing and I kept thinking the distributor bolt was not holding correctly.

 

[jckkys]

I hope your problem isn't as bad as bluebuck's. Steam of course could be what you're seeing. We need some info to answer the obvious questions. Diagnoses is impossible otherwise.