Getting hot on the highway with the AC on.

[RustyRatRod]

One thing I've done to my 75 F250 and the Valiant is use a high flow thermostat. It makes a big difference. So much so with the Valiant that the cooler 160 high flow thermostat helped knock a detonation issue I was having. I know some of the purists will cringe about a 160 thermostat but it made a big difference. Get the Stewart high flow thermostat and get the 160. The theory behind it is, it will open long before the engine tries to see heat soak and keep it from ever trying to get there. It worked for me, naysayers be damned.

 

[toolmanmike]

The patient,
74 Duster
Stock 78 318 with a tiny cam and a 670 Holley on a performer 318/360 intake.
Stock ignition, timing is 20 initial and 32 total.
A-500 OD auto and 4.10 gears.
2500rpm @ 70 mph.
Stock 26" rad that got recored to a 3 core about 3000 miles ago. It's nice and clean!
Underhood AC stuff is from an 80s Dodge truck with an aftermarket cross flow condenser about the same size as the rad.
In car AC stuff is Stock 74 Duster.
It holds steady on 180 which is the thermostat rating around town and on the highway with no AC on.
Yesterday it was 90°f outside and I was taking my son and his buddy to football practice about 30 miles away. By the time I got into city traffic (about 20 mile drive with AC on high) I was tickling the low side of 200°f on the gauge.
I got nervous and shut the AC off after a bit of stop and go in the city with the temp going up to just a hair over 200 on the gauge.
My old 360 (R.I.P.) never got over 180 with all else being the same. Should I even worry about it? I am curious about your opinions on what may be causing this.

Cley
View attachment 1715746405

200° in 90° ambient with the A/C on?
Don't worry about it.
You are almost 60° from boil over with a healthy cooling system and a 15# cap.

 

[Clelan]

Well I'm headed back to the city to watch my daughter play ball this evening. I guess I'll let her heat up a bit more!

Cley

 

[LO23M8B]

I worked for GM in the 90's and 2000's and most cooling fans came on at 217* F. Others most Cadillac's came on at 227* F and that is where they like to run. 200* F makes most engines happy.

That was about the same time GM said spark was the sign of good fuel economy. Lol

 

[LO23M8B]

Let me say one thing i tell everyone Mopars do not overheat. Something is usually broke. At 210 I would be nervous.

 

[Bad Sport]

Well I'm headed back to the city to watch my daughter play ball this evening. I guess I'll let her heat up a bit more!

Cley

I didn't see where you said the hood to core support seal is on the hood. If it isn't that can cause issues, as it allows air to come in between the hood and core support that would normally be coming through the grill.

But if you aren't going over 200* and you aren't experiencing boil over I wouldn't sweat it. These engines were typically put together with 195* stats and designed to run there.

 

[chryslerfat]

Factory Duster fan shroud with a 5 blade clutch fan from the same mid 80s Era Dodge truck that the AC components came from. The rubber seal between the hood and core support is not there but I do have one I could install. I guess I better check my fan clutch is good too. The fact that it's almost new don't mean much these days!

Cley

I didn't see where you said the hood to core support seal is on the hood. If it isn't that can cause issues, as it allows air to come in between the hood and core support that would normally be coming through the grill.

But if you aren't going over 200* and you aren't experiencing boil over I wouldn't sweat it. These engines were typically put together with 195* stats and designed to run there.

I already asked him and he replied it is missing.

 

[yellow rose]

The A/C water pump is the smaller less blade pump. this is so the water moves slower through the rad and gives it more time to cool the water. That is why high flow thermostats never help cool. The water goes through the rad to fast and can't be cooled down. Here is a page out of the factory service manual. Read it. Copy it and save it.

View attachment 1715746476

What year is that FSM?

 

[brian6pac]

What year is that FSM?

I think 1970

 

[RustyRatRod]

Well I'm headed back to the city to watch my daughter play ball this evening. I guess I'll let her heat up a bit more!

Cley

Cley, I do agree with the others that 200.......even 220 isn't over heating. That said, it if was mine, I'd be wanting it "a little cooler".

 

[RustyRatRod]

Let me say one thing i tell everyone Mopars do not overheat. Something is usually broke. At 210 I would be nervous.

That's what I was kinda gettin at. While 200 technically ain't over heating, it's cuttin his leeway a little closer than "I" would want.

 

[Clelan]

So I went in to the city today and the outside temp was about 95°. After leaving my house and driving 70 down the highway for 10 miles with the AC on I pulled in to my wife's office and it was about 195° engine temp. Came back out 20 minutes later and it was about 215 then cooled to 205 in bumper to bumper traffic with the AC on for a half hour. Just for a test I drove with no AC at 55 mph for about 20 minutes and it ran at 195. Maybe it's ok. After my daughter's ball game it had cooled to about 80°f outside and I took freeway and highway home with the AC on and it never topped 190.
I still think I'll put that rubber piece on the hood to seal to the the rad support and double check which water pump I have installed. Maybe a high flow thermostat. If it never went higher than 180 like the old days I'd feel much better!
Thanks for all the input and ideas.

Cley

 

[Ricks70Duster340]

So I went in to the city today and the outside temp was about 95°. After leaving my house and driving 70 down the highway for 10 miles with the AC on I pulled in to my wife's office and it was about 195° engine temp. Came back out 20 minutes later and it was about 215 then cooled to 205 in bumper to bumper traffic with the AC on for a half hour. Just for a test I drove with no AC at 55 mph for about 20 minutes and it ran at 195. Maybe it's ok. After my daughter's ball game it had cooled to about 80°f outside and I took freeway and highway home with the AC on and it never topped 190.
I still think I'll put that rubber piece on the hood to seal to the the rad support and double check which water pump I have installed. Maybe a high flow thermostat. If it never went higher than 180 like the old days I'd feel much better!
Thanks for all the input and ideas.

Cley

You're in good shape, so enjoy your ride!!!

 

[Kendog 170]

I think your ok. I agree about an air dam to get better flow to the condenser. On my ride ( probably not your issue) new build , ran about the same . I thought my Radiator was too small 440 / 500 Stroker ,Champion radiator, I changed out the brand new 180 Stant t-stat that was in it with another 180 T-stat and the car maintains 180 - 190 . Your radiator is huge compared to mine but I have no a/c .

 

[Clelan]

I think your ok. I agree about an air dam to get better flow to the condenser. On my ride ( probably not your issue) new build , ran about the same . I thought my Radiator was too small 440 / 500 Stroker ,Champion radiator, I changed out the brand new 180 Stant t-stat that was in it with another 180 T-stat and the car maintains 180 - 190 . Your radiator is huge compared to mine but I have no a/c .

View attachment 1715746833

That looks nice and clean under the hood!

Cley

 

[MrJLR]

Beautiful Beaker!

Jeff

 

[512Stroker]

The A/C water pump is the smaller less blade pump. this is so the water moves slower through the rad and gives it more time to cool the water. That is why high flow thermostats never help cool. The water goes through the rad to fast and can't be cooled down. Here is a page out of the factory service manual. Read it. Copy it and save it.

View attachment 1715746476

Better not let yellowrose see this post ^^^^^

 

[512Stroker]

The patient,
74 Duster
Stock 78 318 with a tiny cam and a 670 Holley on a performer 318/360 intake.
Stock ignition, timing is 20 initial and 32 total.
A-500 OD auto and 4.10 gears.
2500rpm @ 70 mph.
Stock 26" rad that got recored to a 3 core about 3000 miles ago. It's nice and clean!
Underhood AC stuff is from an 80s Dodge truck with an aftermarket cross flow condenser about the same size as the rad.
In car AC stuff is Stock 74 Duster.
It holds steady on 180 which is the thermostat rating around town and on the highway with no AC on.
Yesterday it was 90°f outside and I was taking my son and his buddy to football practice about 30 miles away. By the time I got into city traffic (about 20 mile drive with AC on high) I was tickling the low side of 200°f on the gauge.
I got nervous and shut the AC off after a bit of stop and go in the city with the temp going up to just a hair over 200 on the gauge.
My old 360 (R.I.P.) never got over 180 with all else being the same. Should I even worry about it? I am curious about your opinions on what may be causing this.

Cley
View attachment 1715746405

Make sure that your lower radiator hose is not collapsing at hi rpm.

 

[j par]

When I put my cold master aftermarket AC in it came with a 12-in pusher fan. it runs off of relay that turns on when anytime the compressor turns on.. that not only keeps the condenser cool but also pushes air when the car really needs it..
I did take the AC to task as soon as I got it all hooked up on the hottest day of the year and it was about 102.. the car stayed right at about 200 to 202 on or off the freeway. although the AC worked great my hands were freezing inside... I did get out into the country and went down a long grated Hill in the trees and the fans turned off and it knocked down to 180... I don't think you're nowhere near trouble...

 

[DrCharles]

Better not let yellowrose see this post ^^^^^

Or anyone else. Sorry, Brian, but you are almost totally wrong. As YR correctly explained early on page 1 of this thread. This stupid urban legend about coolant moving too fast and not giving up its heat is "not even wrong", as Wolfgang Pauli once said. Anyone with the least understanding of thermodynamics, heat transfer and fluid flow would agree.

What you ARE right about is that the a/c pump has fewer blades, but for a completely different reason. The a/c pump stock pulleys have an overdriven ratio (as opposed to the underdrive with the non-a/c pump). That a/c pump is designed to be turned faster so that the fan can be turned faster, thereby providing better cooling at idle and slow speed with the a/c running. It moves about the same amount of coolant as the non-a/c pump since although it has fewer blades it is spinning faster!

That's the last time I'm going to give this speech. Believe what you want - but it's unfair to teach others who may not know better.

 

[DrCharles]

BTW, I have a big-cammed ([email protected]) 451 low-deck, three-row 26" aluminum radiator, 180 Milodon high-flow stat, Flowkooler pump, non-a/c pulleys, Contour electric fans with Autocool PWM controller, 4-speed, 3.91 rear (3050 rpm @ 60 mph). Oh, and no air conditioning.

It will idle at 182 degrees in any ambient between 30's and 90's. But it tends to very slowly heat up on the highway at 65+ (3200) in 90 degree weather, after 15 minutes or so it levels off at 198. The temp gradually comes back down when returning to slow streets or idling, but it takes several minutes to do so.

Anyway, as has been repeatedly said, 200 is not overheating. It bugs me too but I rarely drive the non-a/c beast in 90+ temps anyway! (I'm also missing the seal between the hood and core, will try that eventually. Although with a 6-pack hood, that scoop may be causing issues with airflow too.

 

[brian6pac]

Or anyone else. Sorry, Brian, but you are almost totally wrong. As YR correctly explained early on page 1 of this thread. This stupid urban legend about coolant moving too fast and not giving up its heat is "not even wrong", as Wolfgang Pauli once said. Anyone with the least understanding of thermodynamics, heat transfer and fluid flow would agree.

What you ARE right about is that the a/c pump has fewer blades, but for a completely different reason. The a/c pump stock pulleys have an overdriven ratio (as opposed to the underdrive with the non-a/c pump). That a/c pump is designed to be turned faster so that the fan can be turned faster, thereby providing better cooling at idle and slow speed with the a/c running. It moves about the same amount of coolant as the non-a/c pump since although it has fewer blades it is spinning faster!

That's the last time I'm going to give this speech. Believe what you want - but it's unfair to teach others who may not know better.

First I do understand and what I mean is optimizing the cooling efficiently. When I was racing my car I played around with restricter plates instead of a thermostat. I did have a electric water pump and It ran close to 180* all the time, even on the street with 4.88 gears and a 26" rad. It did take a little longer to get up to temp but that was no big deal. I do know about overdriving the pump It says right in the chart I posted, that's why I posted it so people could read it and see the different things that was done for A/C vs non A/C. It was not to be car specific as the chart was for a 1970 barracuda, that was the car I was racing back in the day.

 

[Clelan]

Well I feel kinda dumb posting this but it was finally hot again today (About 95°) and I was out driving with Max AC on and it never broke 190°. I don't know if I had an air bubble in the coolant or what but it was likely hotter today than when I was having trouble before so maybe I was overreacting. Making a problem where there was not one. I'm kinda bad for that. I'll update here if I have more trouble.

Cley

 

[12many]

Or anyone else. Sorry, Brian, but you are almost totally wrong. As YR correctly explained early on page 1 of this thread. This stupid urban legend about coolant moving too fast and not giving up its heat is "not even wrong", as Wolfgang Pauli once said. Anyone with the least understanding of thermodynamics, heat transfer and fluid flow would agree.

What you ARE right about is that the a/c pump has fewer blades, but for a completely different reason. The a/c pump stock pulleys have an overdriven ratio (as opposed to the underdrive with the non-a/c pump). That a/c pump is designed to be turned faster so that the fan can be turned faster, thereby providing better cooling at idle and slow speed with the a/c running. It moves about the same amount of coolant as the non-a/c pump since although it has fewer blades it is spinning faster!

That's the last time I'm going to give this speech. Believe what you want - but it's unfair to teach others who may not know better.

I get a kick out of the “it never dies theory” of moving the coolant slower in order to draw out heat and lowering temps. Anyone who went from a six vane pump to an eight vane would know it’s nonsense. Funny how you never read of anyone posting of overheating issues running an eight vane only to solve the problem by merely swapping in a six vane. Never. Or lowering temps by swapping from a regular or a high volume mechanical water pump and running an electrical water pump (and its less gph with it’s limited Max running speed)

 

[PredaFran]

The water goes through the rad to fast and can't be cooled down.

View attachment 1715746476

that's not how cooling works. water doesn't work like that it will always be picking up and shedding heat through the radiator. you can either circulate it slowly so the water stays longer, which can cause centralized boiling which will create hotspots, or you can make it pass through the radiator more times in the same amount of time, which is what using a bigger water pump does. it's just an old tale like cars liking exhaust backpressure.