Higher Speed = Higher Temp?

[daddyo23]

I took the '48 on a 450 mile trip to the NHRA nationals in Brainerd, MN. last weekend. Ran with no problem other than when I would run it abit faster, like 70 or so the temp would go up. It was running at 175 at 60, 180 at 65 and 185-90 at 70mph+. I have a 170 thermostat which the local Mopar guru says I should pull out. He doesn't run any in his cars. I'm thinking the timing may be too advanced. I'm open to any suggestions. Thanks, Wayne P.

[41/53dodges]

in my opinion, those temps are pretty good.

as your speed increases, so does the engine speed and required torque, therefore increasing temp.

[Frank Elder]

I have heard of a 160 and 180, where did you get your 170 at?

[TodFitch]

in my opinion, those temps are pretty good.

as your speed increases, so does the engine speed and required torque, therefore increasing temp.

Ditto this statement.

Your internal combustion engine is perhaps 20% efficient. That is only about 20% of the energy in the gasoline is turned into forward motion, the rest is lost. And most of that lost is to heat.

Second, the power needed to over come wind resistant goes up as the cube of your speed. So you needed about about 60% more power to move your vehicle at 70 MPH as you did at 60 MPH. If your forward power went up by 60% then the amount of heat your cooling system needed to get rid of also went up by 60%. Your radiator will be more efficient at higher speeds but not necessarily enough more efficient to make up that difference.

If I recall correctly, the rule of thumb in the 1960s and earlier was that your sweet spot for running cool was about 40 MPH. Enough air flow through the radiator to have it work well but wind resistance was not causing your engine to really have to work hard. At least on the 1992 Jeep Cherokee I once owned that also seemed to be true (ended up with a cooling issue in summer crossing the Mohave).

I am also curious about the 170 degree thermostat. That is what the owners manual for my car recommends but I've only seen 160 and 180 thermostats in the store.

[greg g]

Running with out a thermostat can sometimes cause temps to be higher. In order to be thermodynamically effective, the coolant needs to stay in the radiator for a given period, if it moves through too quickly it will not gain the full effect of the heat exchange. The removal of the stat can cause the flow to be too fast to take heat out of the fluid. Mine runs from 160 to 180 under usual conditions, with a 160 stat. It will run to 190 in high ambient temps or if climbing long hills at speed. I generally watch the gauge on the down hill and it will loose 10 to 20 degrees quite quickly. The other factor is whether your gauge temp reflect accuratly the coolant temp. A thermometer in the radiator will confirm its accuracy within a few degrees. The probe being is a spot that is likely hotter that coolant being returned to the radiator. But if your gauge is off, you're just guessing any way.

Edited August 20, 2010 by greg g

[randroid]

daddyo23,

The increase in friction, both rolling and fluid, will make the engine work harder at higher speeds than lower speeds and that added energy dissipates through the same capacity cooling system as does the energy transferred at low speeds. It takes more energy to drive 100 miles @ 100 mph than it does to drive 100 miles @ 50 mph, and even though there's more air flowing through the radiator at a higher speed air doesn't transfer energy nearly as fast as the cooling water gets hotter.

I read about a car that could do 250+ mph, but a full tank would last only twelve minutes at that speed, while at normal speeds the car could travel more than fifty miles between fill-ups. Same thing. Your numbers sound impressively good and I certainly wouldn't worry about it.

-Randy

[daddyo23]

Thanks for the input. I kinda thought it might be normal for the temp to rise with speed because of factors mentioned and I agree with Greg about having a thermostat in to "slow" things down abit. The 170 thermostat I have is an nos unit. Works well. I have done a temp. check and my gauge is on the money. I just thought it wouild be good to check with the experts on here to make sure things were kosher. The car is running the way it should and will be taking another trip soon. Life is good. Thanks again.

[Jerry Roberts]

There is yet another reason to run a thermostat . The thermostat restricts the water flow until the engine warms up . You want a quick warm up .

[55 Fargo]

I believe 170 t/stats were once being produced, but I am like most everyone, they do not manufacture or sell them today, to the best of my knowledge.......the Rock