While we are on the subject of cooling,,, try blowing out your radiator fins with compressed air . Apply the air from the back , fan side. I was amazed at the amount of crap that came out of my 79SD..

I have to do this all the time with my tractors when I am bush hogging.. My tractors have screens to catch the big stuff , but a radiator will get clogged with dust over time.

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Second owner 1979 300SD 250K miles.
1995 Ford Lightning
66 Mustang
87 5.0 Mustang
08 Ford Edge
46 Willys Jeep
89 Transalp
97 Dodge Ram 2500 Cummins..