After coolant change - high temp at highway speed? 383 Charger

[euroz06]

hi all,

I was in the shop getting some fluids changed, and we noticed that one of the bottom coolant hoses was bad, so we drained the coolant from radiator, replaced the hose and refilled the fluid (of note, my heater valve was closed, and we didn't flush from the engine plugs), closed the radiator cap, started the car. It warmed up, no issue, i drove it around town, no issue, temp is normal. When I got on the highway, cruising at 2.5-3k rpm, the engine temp starts to go way up (at 3k rpm it went up to 240, at 2.5k rpm its at 220). Once i get under 2.5 rpm, the temp goes back to normal. I have under dash mounted gauge that has been pretty reliable (the dash guage is not reading well).

Was there a specific process to do the radiator flush, did we miss a step? I.e. do I have a air pocket now, and how do i get rid of it? I read in the manual, but it talks about doing some sort of pressure refill. Should I open the radiator cap and heater valve and let the car warm up with the cap open to let the air escape?

 

[Bird 426]

Which hose did you replace? Your lower hose may be collapsing if it doesn't have a spring in it.

 

[PurpleBeeper]

Bird 26 makes a GREAT point. Some cheaper lower radiator hoses (suction side) collapse at higher rpm if there isn’t a spring inside to prevent it from collapsing. When cool, you can squeeze in the lower hose and feel for the spring. The spring is about 1/2 as long (?) as the whole lower hose if I remember (?).
2nd guess is what you’re thinking….an air pocket. To remedy that you need a “fail safe” type thermostat OR drill a hole in a regular thermostat to allow air bubbles to escape.
My money is on a cheap lower hose without a spring

 

[gtxdana]

I haven't seen a spring, or the need for one, in a lower radiator hose in decades.

 

[Rishi]

It seems unlikely the intake hose would collapse at highway cruising speeds. Maybe racing it to redline, but not cruising, Shirley?

 

[twecomm]

You really need to "burp" the cooling system after a complete refill to get any air out of the system. Do it with heater on full temp as the heater core is part of the coolant path. Run engine up to operating temp with rad cap off to let air escape. Videos on You Tube if you need..
If all you can find at a local parts store does not have springs, You can find springs that will fit the ID of the lower hose with a Google search. I would not bet the assumption that the lower hose can't collapse , it can under certain operating conditions. A spring in lower hose is cheap insurance against hose collapse. Easy to install the sprig inside the hose. Since you will need to drain the system again to install a spring, good time to Burp the system.

 

[Ron H]

Could be as you say - air trapped. Try running the engine with the cap off and warm enough to open the t-stat, watch for bubbles, and if there they should dissipate. If radiator is dead full, coolant might overflow some and have used a cut out wide-mouth 32oz water bottle in the fill hole to reduce spill over.
As for the lower hose, as mentioned, they can collapse from old age or one that doesn't fit...such as too long. Get a 'formed' hose for this connection for the car.

 

[RemCharger]

The spring in the hose is factory spec for a reason. Sometimes if no one drilled a bleed hole in tstat, can be hard to get initial fill

 

[Bird 426]

Some Ford site has springs for the lower hose , get the right Dia. I can not remember the the site right now. Maybe later. Old age is setting in!

 

[1MYTGTX]

Some Ford site has springs for the lower hose , get the right Dia. I can not remember the the site right now. Maybe later. Old age is setting in!

https://www.cjponyparts.com/lower-r...ss-steel-mustang-big-block-1965-1973/p/HW770/

https://www.cjponyparts.com/lower-r...-steel-small-block-mustang-1965-1973/p/HW769/

 

[Bird 426]

That's it! Thank you!

 

[euroz06]

Thank you so much for quick responses.
So the whole coolant replacement was because we replaced the bottom hose since it appeared to be collapsing (though i've never had overheating issues) due to wear/age. We put in Gates flexible heavy duty hose (my mechanic swears by them - and just responded that its built with a spring), it seemed very sturdy.

Ok, so hopefully the fact that I had my heater valve closed, and didn't run the car to full temp with cap open caused an air pocket. I'll play with it this weekend. Thank you all.

Another question, since you all are so nice in responses. While i was in service, and the car on the lift, i've decided to add some diff fluid (mine has had a sweat on the pumpking/small drops now and then). After adding fluid, it seems like im getting some extra diff chirps at low speed. I then looked in the manual, and it says the car should be on level ground when adding the diff (wheras mine was all the way in the air). So now im a bit concerned that i've over filled it. Should I just undo the bolt whiles its on the ground to let excess get out? Also, any recommendations for diff fluid? I have a 3:55 posi/489 that was built about 6 years ago/8k miles, but its a bit noisy at speed (been like that since day one, but the shop closed, so im stuck with it).

 

[Ron H]

With the fill hole on the side, overfilling will just have the lube drain out. Suppose if car was tipped a bit more opposite the hole, could be more but not much. If concerned, set the car level have some cardboard or something underneath for possible drainage and remove the plug..

 

[Bird 426]

Get used to the noise, don't believe that I have ever had a quiet rear-end. Some are just louder than others. It's either on accel, drive or coast.

 

[Ron H]

Get used to the noise, don't believe that I have ever had a quiet rear-end. Some are just louder than others. It's either on accel, drive or coast.

Yeah – I can 2nd that..

 

[dadsbee]

6 cars and only one has rear axle noise. The Swinger with a "new" Yukon 3.55 set up in it.

 

[khryslerkid]

Ok, so hopefully the fact that I had my heater valve closed, and didn't run the car to full temp with cap open caused an air pocket. I'll play with it this weekend.

Always leave the cap off and let the engine reach operating temperature. Rev it up a little and you'll see the coolant moving past the opening when the thermostat opens. Coolant should be around 1" or less from the top when she's at operating temp.

Also, any recommendations for diff fluid? I have a 3:55 posi/489 that was built about 6 years ago

I use 80w 90w non synthetic but I guess if it has broken in by now a synthetic would be ok.
With a fluid change you need to add 4 oz of friction modifier. It's used in the Sure Grip differentials. "Posi" is a GM term. Motorcraft is a good modifier sold at the Ferd dealerships.

Yes on getting the car level and remove the fill plug for checking fluid level.

 

[BSB67]

What ratio of glycol to water did you use when refilling?

 

[Ron H]

a "new" Yukon 3.55 set up in it.

Just what I have; you must know your rear ends!

 

[euroz06]

so this past sunday, i poped my cap off, got the car idling, but didn't see too many bubles at idle. My idle temp seems to be around 190, so perhaps not enough? I steadily increased the revs to about 2.5k rpm (car warmed up a bit closer to 200), held there for about 30 seconds, and then released, went to look at the radiator and saw bubles coming out. I did it a few more times until i couldn't see the bubles anymore. Went for a drive (this time not highway, just in 1-2nd gear above 3k rpm), and im again overheating. ugh... I looked up burping on youtube, and they recommend raising the front of the car so the trapped air can escape, so i think i will try that next. Another question, with the radiator cap off, can I run the rpm's to 3k? I was a bit scared to do it at 2.5 for fear of it shooting out (im very new at this, so pardon for lack of knowledge... i looked at the manual, and they just use some old tool to do all this).