Does your car run hotter at higher speeds?

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danielb927

danielb927

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I'm currently driving cross-country along Route 66 and the car's running hotter than usual. For starters, I don't know what thermostat the PO put in it but I'm guessing a 160* but possibly a 180* (for reasons below). The radiator also has a small crack that I fixed with JB-Weld a while ago, so when I get where I'm going, I'm putting in a new radiator and a 180* t-stat. Looking back, I would have done that stuff before leaving, but too late now, I just need it to hold up for another 1500 miles in the next week.

Any rate, the temp gauge always used to sit right up against the first line in the "normal" range (that's why I'm guessing it's a 160* thermostat, possibly 180*) but on this trip it's run 1-2 needle widths away, sometimes creeping up towards being totally vertical. I'm assuming to some degree that's normal given that it's 95 degrees outside. But the last couple of days I've been keeping it to around 55-60 mph because it runs cooler there than at 65-70 mph, so I'm wondering - is this normal? Or just another indicator that the radiator is in need of replacement?
 
I,m guessing here but maybe the higher rpms runs the water thru a little faster and it doesnt have as much time to dissapate heat. I wouldnt worry about 2 needle widths.
 
I've been driving my 68 dart for about 8k miles. So far on the freeway at around 70ish, or higher, it stays hot. Once you back off to 60, it cools down, and idle cools it down further. Switching the heater on allows you to drive slightly less hot. I have literally replaced every cooling piece on the car - except the radiator. I even took the head off and cleared the water pathways and still heats up. I flushed the radiator and the car doesn't heat up as much. The water pump replacement made the car heat up faster and I believe the car has a 180ish thermostat on it. New pump, hoses, head gasket, cleaned the ports, new fan, etc... So I bought a radiator, and I'm putting it in tomorrow. The only other thing I could think of is the oil pump not pushing well, or the oil filter clogged. Not sure, but oil filter is brand new.

I've had the same issue for a while as you have, and tomorrow when I swap in the rad, I'll let you know if that fixed it. Likely you have the same thing and the rad is just clogged. I've been dealing with the high speed issue for a while, but can only stay on the freeway for about 20 minutes, so if you're in a lengthy drive, either your rad is clogged less, or something completely different.
 
I had the same problem, but a new aluminum rad from Champion Rad fixed my problem. I would put a 180-185 thermostat in at the same time. Good luck!
 
if the car heats up at low speeds/idle then its not enough fan. if it heats up at high speeds its not enough radiator. I would check your water level. the factory gauges are extremely inaccurate. to really know what is going on you need an aftermarket gauge.
 
Mine runs hotter on the open road but I attribute it to the low gears (3100 rpm at 55 mph). The only time I've ever seen my temp up to 200 was after a 25 miles cruise.
My electric fan is also on the outside pushing air in.
 
danielb927 said:
I'm currently driving cross-country along Route 66 and the car's running hotter than usual. For starters, I don't know what thermostat the PO put in it but I'm guessing a 160* but possibly a 180* (for reasons below). The radiator also has a small crack that I fixed with JB-Weld a while ago, so when I get where I'm going, I'm putting in a new radiator and a 180* t-stat. Looking back, I would have done that stuff before leaving, but too late now, I just need it to hold up for another 1500 miles in the next week.

Any rate, the temp gauge always used to sit right up against the first line in the "normal" range (that's why I'm guessing it's a 160* thermostat, possibly 180*) but on this trip it's run 1-2 needle widths away, sometimes creeping up towards being totally vertical. I'm assuming to some degree that's normal given that it's 95 degrees outside. But the last couple of days I've been keeping it to around 55-60 mph because it runs cooler there than at 65-70 mph, so I'm wondering - is this normal? Or just another indicator that the radiator is in need of replacement?
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All this tells me is that you don't have any idea what temperature your car is running.

Put a real gauge in it then you will know. You may not have a problem at all.
 
1968FormulaS340 said:
All this tells me is that you don't have any idea what temperature your car is running.

Put a real gauge in it then you will know. You may not have a problem at all.
Click to expand...

I agree with this 100%, but I don't plan to put in an aftermarket gauge in the middle of a long haul.

Appreciate the quick advice from everyone, that gives me more peace of mind while driving it the rest of the way. Sounds like if I keep on keeping it reasonably cool towards what I'm used to seeing, it should be fine.
 
danielb927 said:
I agree with this 100%, but I don't plan to put in an aftermarket gauge in the middle of a long haul.

Appreciate the quick advice from everyone, that gives me more peace of mind while driving it the rest of the way. Sounds like if I keep on keeping it reasonably cool towards what I'm used to seeing, it should be fine.
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could be air going under the front of the car and conflicting w/ radiator air flow. that`s why most new cars have spoiler type fronts, or long reaching plastic bumpers. had the same trouble my self on a 406 vega, home made front spoiler fixed it.---------bob:coffee2:
 
younggun2.0 said:
if the car heats up at low speeds/idle then its not enough fan. if it heats up at high speeds its not enough radiator. I would check your water level. the factory gauges are extremely inaccurate. to really know what is going on you need an aftermarket gauge.
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On the money younggun2.0

oh, and it doesn't matter if you've just had it flushed, even if the water coming out was like spring water, it could still look like this on the inside.
from that link you can see just how bad the stock manufacturing process must have been. Both radiators had many core tubes plugged with solder from what looked like the dawn of time.

I still think you'd need a real temp gauge to see if 2 needle widths is even something to worry about...could be that the flush has made the temp sender more sensitive because it doesn't have a layer of crap on it, or could be that the temp is just fine and the gauge is going south... :lol:
 
How is the hood to radiator seal? Also the vacuum advance and proper timing is important at cruise. Retarted timing increases engine and underhood temperatures.
 
Well, I installed the new radiator. Car doesn't even get remotely as hot on the freeway. It stays at a constant toward the colder side of center.
 
my running 'hot' on the highway was a too lean condition....fattened it up and no more problem...this was after redoing the radiator, water pump, etc....
 
Maybe I need to do the same to my carb. I literally just went on a drive and I have replaced every piece of cooling equipment. Started heating up too much again.
 
get a good aftermarket gauge first then see what the deal is if you don't like the look of aftermarket tuck it up under the dash when you don't need it???
 
Where are you at now Daniel? I'm just 3 miles off Rt. 66, 10 miles south of Litchfield. I imagine your already past me but if your not and can stop by I have a thermal temp gun and we can check the accuracy of your gauge real easy. As the others mentioned factory gauges aren't very reliable, especially when their 40+ yrs. old. I'll shoot you a PM with my ph # so you can catch me any time
 
fishy, I'm already down in New Mexico. Would a NAPA store be able to shoot a temp gun at it? If so, where would you aim it to get an accurate reading?
 
danielb927 said:
fishy, I'm already down in New Mexico. Would a NAPA store be able to shoot a temp gun at it? If so, where would you aim it to get an accurate reading?
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Not sure if a NAPA would have a temp gun to use or not. I'm sure they sell them, but they may not have one to use. Autozone is usually better at doing stuff like that. Shoot it at the thermostat housing (if it isn't chrome, reflection off of anything shiny can give a false reading). The temp will be a few degrees hotter than the reading your get off the thermostat housing because your only reading surface temperature, but it'll be close. If you have a chrome housing shoot the water pump and/or timing cover. That's a good close second.
 
Thanks, might try that. Today, with temps in the 70s all day, it ran right on/against the line like it usually does at home, even for 90 minutes of straight cruising at around 62 mph. So that was nice.
 
Your welcome Dan. Outside temp sure can make a big difference. Mine runs 180 all day long when it's 80 or less. Soon as it hits 85 mine's up to 190~195. 90 outside and it runs right at 200. Some are just touchy like that.
 
Any engine will run warmer with it working harder.

But...
- scaled-up radiator
- retarded timing
- lean mixture
- blocked airflow (large transmission coooler fi)

These are the things that can/will increase engine operating temps by itself.

My own '73 Dart has an old scaledup radiator and it causes engine temps to start rising above 195-200deg. above 70mph.
Below that it can drive or idle all day in 80deg heat.
 
fishy68 said:
Your welcome Dan. Outside temp sure can make a big difference. Mine runs 180 all day long when it's 80 or less. Soon as it hits 85 mine's up to 190~195. 90 outside and it runs right at 200. Some are just touchy like that.
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That's almost exactly what I've seen (except for not knowing the actual numbers). 70s the last 2 days so it's run right where it always does, and the engine survived a downpour on the interstate with the newly-functional ram-air scoop, so things are looking good :thumblef:
 
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