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Ever since I went from my 2.79 peg leg 8'' to a 4.11 detroit locker 9'' my mustang runs hotter on the highway. I took off the old junk iron repo water pump and went to a higher flow aluminum GMB water pump that is supposed to eliminate cavitation and it took it down about 10 degrees.

I use a two row aluminum radiator and syclone 2500 cfm fan, overflow tank, and 22lb cap (I checked and the system holds that pressure fine). Also I run the high flow aluminum water pump noted above with 180 degree high flow balanced thermostat from stewart.

The above cooling system kept the car at a constant 180-190 no matter what temp it was outside with the old rear end. Now it seems that coolant will go into the overflow when it doesnt even appear to be overheating. It also runs 200-215 on the highway and about 190 around town. I used to have the opposite problem before i upgraded all my components too cool better. Why would it run slightly hotter on the highway now? I don't have any real signs of head gasket leaking. It runs strong, holds 12'' vacuum at idle, and doesnt seem to have coolant in oil or via versa.

I drive slower than I did before the gear on the highway now so I keep it at the same 3000-3200 that I did before but it is just at 55-60mph instead of 70.


Any ideas guys? I am about broken down trying to figure this one out just like my popping noise in the other thread. This car is my baby and it is running very strong and hard so I don't see how it could be something major like a head gasket. Maybe its time for a compression test to be sure?


Thank ahead of time...

-Nick
 

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Try replacing the radiator cap. It may not be holding pressure anymore. Is there any possibility that the fans can be turning the wrong way? If the + and - leads were reversed, most DC motors i've been exposed to will turn the opposite direction. Are the fans turning on?

Lastly, i'd check the thermostat in boiling water to see if it is opening completely. With no additional load on the car, I really don't think the engine should run much hotter than before. The engine should have an easier time at it with 4.11s. It's rotating faster so there may be some additional friction and resulting heat, but your system should handle it easily.
 

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Try advancing your timing. I was having similar issues and I advanced just a touch and it brought running temp down 15 degrees.
 

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I have several post on what my cooling issue was I have a 545 871 fuel injected big tire car 4:56 and I pulled every hair I had out I checked head gaskets I used 3 different radiators I had 5 different fan set ups restrictor plates electric pumps if it was cool out I ran 200 if it was above 90 out 235 and never came down now I run 195 to 208 at 95 outside I listened to a older guy over at afco I put in a dual pass radiator a stock 180 stat a electric 35 gph pump 50/50 green 1 pint of afco water wetter solved my problem my motor was making a amount of btu that the radiators could keep up with I needed to coolant to run in the radiator longer at the same rate of flow and that fixed me right up
 
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