Proper coolant………
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Mountain Pass
Joined: Aug 2025
Posts: 101
Likes: 20
Proper coolant………
For 1991 7.3L? I’m sure this has been covered before, was engaged in a debate over on Red Power Magazine(IH), concerning the proper coolant for older Navistar engines. My 1991 7.3L currently has the red extended life coolant, truck still has the original copper soldered radiator, should I flush system(many times) and go back to green? TIA
Logistics Pro
Joined: Jun 2017
Posts: 3,986
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From: Edmond, OK
I use green concentrate Peak coolant mixed 30%/70% with distilled water and a Wix 24073 coolant filter.
https://www.ford-trucks.com/forums/1...-9-diesel.html
If you don't run a coolant filter pre-charged with SCAs then you need to run a coolant that has them. They prevent the block from cavitating.
https://www.ford-trucks.com/forums/1...-9-diesel.html
If you don't run a coolant filter pre-charged with SCAs then you need to run a coolant that has them. They prevent the block from cavitating.
Lead Driver
Joined: Apr 2002
Posts: 5,380
Likes: 1,263
For copper and brass stick with original green. I use a 50/50 mix with distilled. My local radiator shop recommends original green. Your mix may vary by your weather in your area. How cold does it get? Follow the protection mix required for your coldest expected temps.
I also add the Motorcraft DCA diesel coolant additive as recommended.
I also add the Motorcraft DCA diesel coolant additive as recommended.
Last edited by BigBlue2; Mar 2, 2026 at 11:18 AM.
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Mountain Pass
Joined: Aug 2025
Posts: 101
Likes: 20
Thanks everyone, a previous owner had switched over to red extended life coolant. I need to switch out the thermostat that was replaced while on a road trip this past October, all that was available at the time was 195 deg from NAPA. Temp gauge now only gets to just touch the ‘N’ on normal, when before it would ride on the upper side of ‘O’ at highway speeds. Will change both when I get everything rounded up.
Laughing Gas
Joined: Mar 2016
Posts: 1,105
Likes: 78
There are 2 temp range thermostats available, you must have been given the cold one. The cold one is too cold. 1807974C94 is perfect warm.
The good thermostat is 1807974C94, I would buy an international harvester new old stock one and avoid parts brands or the dealership replacements.
The good thermostat is 1807974C94, I would buy an international harvester new old stock one and avoid parts brands or the dealership replacements.
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IDI-Charlie
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