'70 Charger Overheats after 40 minutes on highway today [but before this it did not overheat at idle or shorter trips]

[matchek]

Hi, I am stumped as to what is going on with my cooling system. Today after driving on the highway around 40 minutes from the shop for work that supposedly had nothing to do with the cooling system, the car overheated (temperature to 250F). I had the car two years and have not driven it much. This is longest distance I ever drove it. To clarify, I had work done on the car. Before I picked it up, the mechanic test drove it for around 10 miles and this morning I test drove it for around 5 miles around town. The car was running very well for both us. To get home, I drove around 5 miles on city roads with several stop lights (no overheating - Temp at ~ 185 F), then drove around 30 miles on the highway between 60 and 80 mph (no overheating - Temp ~185F). On around the 35th mile while going around 65 mph on the highway, almost home, the temperature climbed from 185 to 235 F in what seemed around 3 to 5 minutes in a steady clockwise fashion. Luckily I was routinely glancing at the gauges. At that point, when I exited off the ramp and sat at a traffic light, the temperature then went quickly to 250 F where I pulled over and shut the car off. Did not see steam from the engine or the radiator. I did notice a little fluid dripping off the front behind the license plate [ at that time did not notice where exactly it was dripping from]

Extra info: I had the car for 2 years where I typically idle the car in the garage or have taken short 10 miles trips and never experienced any overheating. Did not drive it much because I had brake problems which are now fixed. Today, the car drove great for the first 35 miles and then started overheating at around the 36th mile.

After letting the car cool for 4 hours, I opened the radiator cap and and to my surprise not that much liquid was gone. I added about one quart of 50/50 coolant and topped it off. II remember from reading the manual not to top it off entirely and did not before, but today I did for reference). I started the car and let it run for around 10 to 12 minutes. After around 5 to 8 minutes, some water overflowed out of the radiator overflow hose, and the the temperature was again rock solid at around 185F while idling the car in the driveway and then I shut the car off (185 F and not overheat) The water level remained mostly at the top or close to it while this idling. The oil was not brown and the top radiator hose was warm when running. I did not notice any steam coming from the head gasket, water pump or radiator.

Any ideas as to why car overheating while driving this extended trip at speeds of 60 to 80 mph, but when I idled it in the driveway it was stable at ~ 185 F again? I am glad it running well again in my driveway, but I am afraid to drive it. I ordered a a new thermostat for good measure. Since I got the car the radiator I did not flush the system. It looks like in great condition and the water level is always on the high side so didn't think it was a problem. Thinking perhaps something could be blocking at high speed.

As far as driving he did install a new distributor and adjust the timing. He also removed and reinstalled the transmissions to replace seals (I have to take it back because after I restarted it after the install, the car shifts to neutral after about 15 seconds and the mechanic said it was not tighted well enough after reinstall). I speak to this more in a post later in this thread.

 

[1 Wild R/T]

No steam? Did the engine ping at all, did it feel or act hot? Any chance the gauge was acting up?

 

[Jerry Hall]

Could be that the thermostat stuck for a little while. After cooling for the 4 hours, it released. I would flush the cooling system and replace the thermostat and try again.

 

[1 Wild R/T]

Could be that the thermostat stuck for a little while. After cooling for the 4 hours, it released. I would flush the cooling system and replace the thermostat and try again.

I tend to agree, the fact it runs for thirty plus minutes rock steady then suddenly spikes tends to point to a gauge or a thermostat...

 

[Kern Dog]

I wrote about this with one of my cars too:

Overheats on the freeway but not when cruising around town?

I haven't figured out exactly what is to blame. I've replaced the thermostat and radiator and added a shroud. I've yet to take it out on the road.
It didn't overheat while cruising around or even hot rodding it. It only did so on the freeway.

 

[#41]

I'd agree with above as the simplest solution: Thermostat not opening all the way or perhaps gauge or sender malfunction. Buy yourself a cheap thermal gun to check temps at the thermostat area and water pump.

 

[Geoff 2]

Replace t'stat first. Cheap & easy to to do...
If the rad is old, it can clog with sediment in the tubes. Especially with a X flow rad because the tubes are horizontal & the lower tubes gradually block up so that the problem goes unnoticed until the engine is under more load....such as high speed driving.

If the performance has not dropped off, it suggests the engine tune is ok & is not the cause.

 

[68gtxman]

Your issue sounds like one I had when I changed to a high stall speed torque converter. Using the standard TC, I had no heat issue, but after changing to the higher stall speed TC, I now have a highway overheat issue - never around town or just idling. I added two small transmission heater exchangers, in series with the lines going to the radiator and that helped a little. But this did not resolve my highway problem entirely. My plan is to return to a stock TC. Good luck with your issue!

 

[Frank Mopar]

Not going to fix the overheating but you need to put in coolant recovery system. A Stant 10231 cap and a coolant recovery bottle of your choice. Make sure the hose between is clamped tight

This keeps the radiator full and coolant off the ground.

 

[matchek]

Thank you gentlemen. Alhtough it could be of course, I don't think it is the gauge because the gauge did not go nuts, it was very calm as it went up and also when I pulled over, a good amout of dripping occured from below the license plate area after I shut the car off - not a ton but enough to know that was not normal and never happened to me before. My hunch is that is was from the radiator overflow hose but not sure I was parked in a Tow Away Zone and was working on not getting towed. Thermostat does sound likely or sediment too. The radiator look like it is in good shape - I will ask the previous owner if he know how old it is. Of course don't know what it is like on the inside.

By the way, I want to add something to see if this has anything to do with it since 68GTXman mentioned the transmission torque converter. As I mentioned in another thread, I had a leak in the transmission and the mechanic wanted to remove the transmission to replace a small seal the size of a quarter. From my understanding he replace that little seal and also the torque converter seal. To make a long story short I let him remove the transmission and re-install he said he was adamant he didn't enough of room. The mechanic test drove it for 10 miles. When I picked it up yesterday, I test drove it around town there for 5 miles and there were no transmission leaks and the automatic transmission was fine. Car ran great. Also on the 35 mile trip home, it drove great [city driving and highway driving 60 to 80 mph]. HOWEVER, after letting it sit and cool for 35 minutes, I started the car and drove it the last mile home. When I did, the transmission kept wanting to shift into neutral. The car kept on shifting into neutral unless I drove with my hand tugging backward keeping it into the DRIVE position while I drove the last mile home. If I let my hand off the shifter, the shifter would gently slide back into neutral for about 20 seconds and then shift into neutral. (It did not do that on the first 35 mile part of the trip, just after the overheating espisode).

When I called the mechanic to tell him what was going on and what happened, he apologized and said that when he test drove it for 10 miles it was fine, but his mechanic must not have tightened the transmission linkage enough after he reinstalled it and he'll take the car back to have it adjusted. I did not think the tranmission has anything to do with the car over heating, but I thought I would mention due to what 68GTX man said about the torque converter. Could this transmission issue have anything to do with my problem? Thank you!

 

[matchek]

Your issue sounds like one I had when I changed to a high stall speed torque converter. Using the standard TC, I had no heat issue, but after changing to the higher stall speed TC, I now have a highway overheat issue - never around town or just idling. I added two small transmission heater exchangers, in series with the lines going to the radiator and that helped a little. But this did not resolve my highway problem entirely. My plan is to return to a stock TC. Good luck with your issue!

Thank you 68GTXman, I did have the tranmission removed and reinstalled and had a couple seals replaced included the torque converter seal. And after overheating the car wants to drive into neutral while driving and the mechanic told me it was just an adjustment that was not full tight after reinstall. I detailed above. Not sure if this adds to the overheating? Thank you for mentioning.

 

[matchek]

No steam? Did the engine ping at all, did it feel or act hot? Any chance the gauge was acting up?

I did not see any steam that was noticable. It could be my hunch or because I was terrified, it appeared that power was diminishing. Also when I went to restart it I had to give it gas when before I didn't. It could be be the gauge but doubt it because of how it acted, it seemed to over heat in a calm clockwise fashion, and then went to 250 F quick after I exited the highway and was sitting at the traffice light before I went to park and shut it off. I thought I could smell coolant but not overwhelming. It just seemed like something was wrong and not just a gauge.

 

[Jerry Hall]

You have opened a whole new can of worms, with possible transmission issues. Excessive heat buildup in the transmission with the fluid being cooled by the radiator can raise coolant temperatures. Now with the transmission not acting right, check your transmission fluid color and smell. A dark color and burnt smell is not good. Recent work even in other areas can lead to problems elsewhere. Just my opinion.

 

[matchek]

You have opened a whole new can of worms, with possible transmission issues. Excessive heat buildup in the transmission with the fluid being cooled by the radiator can raise coolant temperatures. Now with the transmission not acting right, check your transmission fluid color and smell. A dark color and burnt smell is not good. Recent work even in other areas can lead to problems elsewhere. Just my opinion.

Thanks Jerry, I did check the tranmission fluid ( which was recently replaced) is still clean and light pink.

 

[matchek]

Just a FYI, the mechanic did not think the overheating has anything to do with the transmission as long as there were not leaks and appears there were not. Not arguing with that, but just relaying.

The mechanic really thinks its the radiator (most likely) and secondary water pump. He does not think it is the thermostat. He wants me to either get a new radiator or have it taken out and cleaned by a shop.

One thing of notice is when I drove the car to the shop two months ago and ran the car from 60 to 70 mpg for 30 miles or so it did not over heat.

The mechanic did agree if I did not want a new radiator to just flush out the system and install a thermostat he would do so. I think it is a little overkill to just install a new radiator from the get go.

 

[Don Frelier]

Just a FYI, the mechanic did not think the overheating has anything to do with the transmission as long as there were not leaks and appears there were not. Not arguing with that, but just relaying.

The mechanic really thinks its the radiator (most likely) and secondary water pump. He does not think it is the thermostat. He wants me to either get a new radiator or have it taken out and cleaned by a shop.

One thing of notice is when I drove the car to the shop two months ago and ran the car from 60 to 70 mpg for 30 miles or so it did not over heat.

The mechanic did agree if I did not want a new radiator to just flush out the system and install a thermostat he would do so. I think it is a little overkill to just install a new radiator from the get go.

You can pretty easily tell how well a radiator Flows with the lower hose loose and a garden hose.
Or dump a 5 gallon pail of water in it.
You can also tell somewhat visually just looking inside.

 

[matchek]

You can pretty easily tell how well a radiator Flows with the lower hose loose and a garden hose.
Or dump a 5 gallon pail of water in it.
You can also tell somewhat visually just looking inside.

You mean when you loosen the bottom hose so some drips out and all the while running it with a garden hose putting fresh water in the top?

I looked in and it is not terrible, I have seen worse. But I can only see just a couple of inches left or right of the radiator cap.

 

[1 Wild R/T]

Looking inside is a crap shoot, most of the debris will be in the bottom of the tubes...

Any hard debris winds up trapped in the tubes of the radiator.... If you have an old school radiator shop in your area pulling a tank & rodding out the tubes was a common solution back in the day...

However a plugged core doesn't run cool then suddenly spike, depending on how plugged it can slowly creep toward overheat, or start getting hot soon after the car is started.... But not run cool for a half hour then suddenly get hot...

 

[matchek]

Looking inside is a crap shoot, most of the debris will be in the bottom of the tubes...

Any hard debris winds up trapped in the tubes of the radiator.... If you have an old school radiator shop in your area pulling a tank & rodding out the tubes was a common solution back in the day...

However a plugged core doesn't run cool then suddenly spike, depending on how plugged it can slowly creep toward overheat, or start getting hot soon after the car is started.... But not run cool for a half hour then suddenly get hot...

Yeah it ran 185 F for 35 miles from 60 to 80 mph and on the 35th mile it drifted from 185 to 235 within a couple minutes or so almost like a slow ticking clock ticking clockwise. The next day it is idling at 185F sitting in my driveway.

 

[1 Wild R/T]

Whether your mechanic thinks so or not I would do as Jerry Hall suggested & put a thermostat in the car..