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440 Running Warm - Why

MoparHonda

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I have a '70 Plymouth with the 440/6.

Car has a 160 degree thermostat. Car runs around 170 degrees in town, idling at lights, cruising the neighborhood. Car goes to to about the 200 degree range in the interstate at 65-70 mph. Car drops back to the 170 degree range as soon as I get off the interstate. Why?

New radiator core (stock radiator), new thermostat, new hoses, system flushed, new coolant.

Why does this run about 30 degrees hotter at 65-70 mph on the interstate?
 
Another member just dealt with this same issue. Try searching for that thread. I believe he solved it.
 
You're lucky, mine was upwards of 230 during Hwy speeds 210 around town. Was using an old radiator. Swapped in a 26" 2 row 1"tube aluminum rad and my first Hwy run was at 189.... either your water pump can't keep up at those RPM's or your radiator is not flowing good.
 
Agreed on the radiator being the possible cause, but it's the correct numbers matching stock 26 inch radiator and it's been recored by a well known and recommended shop here in town. The same shop has done work for me and other collector car people with no problems.

Why would the water pump not be able to keep up? I would hate to spend the money to replace it and still have the problem.
 
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Is it overheating? Check pressure cap, your engine same as mine calls for a 195* thermostat, factory specs for a 440/6. If problem has suddenly arisen. You may need a new pump, here is my set up I had an issue over heating I flushed heater core block ,changed pump, it was the pressure cap,but I went to a 195* from a 180* thermostat ,around town I'm at 185-200 on ex way I'm at 190
 
At idle it stays cool so it has enough air flow and water flow. At speed it should have even more... so either the motor is making more heat at speed than it should (timing / lean) or the increased demand isn't being met with an increased water flow (water flow restriction - suction hose collapsing / pump clearance I.e. gasket the wrong)

That's my guess.
 
HT possible, but I've had thermostats F -ck up when new, make sure it's not a GOOK THERMOSTAT!!!
 
I have a '70 Plymouth with the 440/6.

Car has a 160 degree thermostat. Car runs around 170 degrees in town, idling at lights, cruising the neighborhood. Car goes to to about the 200 degree range in the interstate at 65-70 mph. Car drops back to the 170 degree range as soon as I get off the interstate. Why?

New radiator core (stock radiator), new thermostat, new hoses, system flushed, new coolant.

Why does this run about 30 degrees hotter at 65-70 mph on the interstate?
what rear gear are you running?
 
Are you running a fan clutch? Slipping at higher rpm?
 
Thank you all for answering.

Car does not overheat, 230 is considered overheating, car only goes up to about the 200 range.
Radiator cap seems to hold the pressure, cap seems good.
Hoses are new, nice heavy thick ones, doubt it's collapsing, hoses look good visually as soon as I pull off the interstate.

I have a 354 rear, about 3500 rpms on the interstate.

HT413, you say pump clearance? Do you mean it may have the wrong gasket in the water pump and that's causing a partial blockage? (I've never had the pump off.)
 
Well, for what it's worth I just had the same issue with my new to me 440 I just installed. I wound up replacing the whole dang cooling system, but on the advice of Professor Rick Ehrenberg, I bought a Griffin "exact fit" 26" aluminum radiator.
I had the same issues - the car ran acceptably cool at idle, but would get quite warm at highway speed - too warm for me.
Winds up, I didn't have enough radiator.
Number of "cores" doesn't matter - total surface area of tubes/rows per inch does.
This Griffin has a 3" thick core (!) and consists of two rows of 1.25" tubes at a rate of 16 rows per inch.
Yeah, that's dense as hell. Lots of surface area for cooling.
I also installed a Mopar shroud and a direct drive 18" fan, since there wasn't enough room for even the really short fan clutch. 180 degree SuperStat with a few holes drilled in it for burping purposes.
BTW, I also installed a spring in the lower hose - I have seen those collapse on these engines!

Results? The car now struggles to even make it to 180 degrees going down the highway and actually goes up about 20 degrees when I get caught in traffic.
What is happening there is that the fan/shroud combo, as big as it is, simply isn't drawing enough air through that DENSE radiator core!
I'll fiddle with sealing off the edges of the shroud and all that, might even go with a 19" fan since the shroud seems to allow for one - but I can drive all dang day at any sort of speed and the car runs cool!
Happy boy here. :)
 
Thank you very much, so the consensus is that I don't have enough radiator? I already have the stock shroud and stock fan with clutch.

Since a spring in the lower hose is easy and cheap to do, I may just try that and see what happens.
 
I have a buddy who used to work at a radiator shop back in the mid 70's, said Chrysler had the worst factory radiators. Always coming in plugged up, and never good enough to keep up with engine demands. Yours might've been recored, but still might not be up to the task. My local radiator shop always likes to recore with the least amount and largest tubes the factory tanks will accept, another words the stock stuff isn't enough !
 
Thank you, didn't know the factory radiators had a reputation of not being adequate.
 
3500 rpm at hi way speed seems a little high to me for the gear you have. I run 355s at 3000 rpm I'm doing 70 with a 4200 stall. Is yours standard or auto?
 
I have a 26 inch stock radiator in a highly built 383 high-volume water pump 180-degree thermostat and this thing runs well below 180 everywhere no problems. Also have a mechanical gauge that reads below 180 the factory gauge reads well below half.
 
Why would you suddenly not have enough radiator in your car? I have run a warmed up 440 behind a 22 inch radiator and got by fine. Test your fan clutch. If it is not grabbing when the temp goes up it's time for a new one. They do go bad.
 
Thank you, didn't know the factory radiators had a reputation of not being adequate.
I dont think unless one was old enough to actual have one of these cars back in the day that they can and did overheat. I had a completely stock brand new condition 1969 GTO in 1971. No AC and on a hot summer day it would run hot on the highway. In stop and go traffic it would go up above 200 and could overheat. When i think back, overheating cars was a normal sight in stop and go traffic in the summer time. My thinking is if the rest of your cooling system is in top shape, engine is tuned properly and it runs hot like you say, you need more radiator.
I just went through this with my stock AC 383. I had a 160 thermostat, 26 inch three core radiator and the car was not getting hot enough. A switch to a 180 did the trick
 
Why would you suddenly not have enough radiator in your car? I have run a warmed up 440 behind a 22 inch radiator and got by fine. Test your fan clutch. If it is not grabbing when the temp goes up it's time for a new one. They do go bad.
If the clutch is bad, that would explain an issue with temps at idle, not at highway speed.
 
If the clutch is bad, that would explain an issue with temps at idle, not at highway speed.
Agreed. He seems to have plenty of cooling around town but when he is cranking 3500 rpm for an extended time down the interstate his temps are climbing. If he has a thermal fan clutch it should be grabbing when the temps get above 180 behind the radiator....correct?
With a 160 thermostat he is making his operating range much larger and open for larger temperature swings. Is a 30 degree swing just normal for this set up? Or should the fan and clutch be holding the temp lower?
 
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