Filling Late Model SN-95 Cooling Systems
| 31 January 2004
Back in December 2001, I wrote my very first Pony Trick column for Pony Express. I called it “changing antifreeze” and it was primarily an article on how to mix antifreeze with water to achieve the desired ratio. It touched only briefly on the need to make sure the cooling system was properly filled. It was short and contained minimal detail. But it was directed toward the first generation cars where “short without a lot of detail” just about covers the waterfront.
This Pony Trick talks about the same topic but it’s directed toward the late model cars. Making sure you have the correct antifreeze ratio follows the same guidelines but the fill procedure is more complicated than just pouring antifreeze into a radiator and topping up with water. Before I get to the fill procedure, let’s talk briefly (again) about mixing the antifreeze. And I’m assuming that you’ve already drained the cooling system and performed any other maintenance such as flushing, washing-out the degas bottle, changing hoses, and/or replacing the thermostat.
Unless your engine is freshly rebuilt and you’re filling a totally empty cooling system, there’s a residual amount of liquid in the system. It might be as much as 20%. The point is, it’s there, you can’t get rid of it, and you can’t tell how much you actually have. With that in mind, how do you mix your antifreeze and water so that it falls in the 40% to 60% range specified by Ford? If you premix to, say, 50/50 and pour that mixture into the cooling system, it will be diluted by the residual solution. So don’t premix.
Look up the capacity of your system and then calculate half of that amount. The answer to your calculation is the amount of straight antifreeze to use. Pour it into the system right out of the container. Now add distilled water until the system is filled. That approach gives you a 50% solution if all your residual is water, like it would be if you flushed. Or it gives you slightly more that 50% if you didn’t flush and the residual is your old solution with some percentage of antifreeze in it.
With the mixing step out of the way, let’s look at the fill procedure. The 3.8L V-6, the 2-valve 4.6L V-8, and the 4-valve 4.6L V-8 all use different procedures except that each procedure requires you to set the heater temperature control to maximum and each procedure requires that the pressure relief cap be removed from the degas/coolant recovery bottle.
First, let’s look at the V-6. Locate the cooling system vent plug on top of the fitting near the front of the engine. It’s the fitting where the bypass hose attaches. Remove the vent plug from the top of the fitting. Fill the system at the degas bottle but when the bottle indicates full, add additional solution at the vent plug opening until it’s ready to overflow. Install the vent plug and tighten it. Do not install the pressure relief cap on the degas bottle.
Run the engine until it’s up to temperature. Shut the engine off and after it cools, add 50/50 antifreeze premix to the degas bottle, if the solution level is below the mark. That’s right 50/50 premix at this point because you already produced a 50/50 mix in the rest of the system when you used straight antifreeze and then finished filling with distilled water. Now replace the degas/recovery tank cap, set the heater temperature control to maximum, set the heater air flow control so that air will discharge from the dash vents, set the heater fan control to maximum, and then start the engine again. Allow it to run at idle until it warms up. Hot air should discharge from the dash vents, the temperature gauge should read normal, and the upper radiator hose should be hot.
If those criteria are not met, shut the engine off and let it cool. Add 50/50 premix solution to the degas bottle to bring the level up to the mark; remove the vent plug again and top up at that location too. Put the plug back in place, replace the degas bottle cap, and start the engine for another test. Repeat as necessary until the dash vents deliver hot air, the temperature gauge reads correctly, and the upper radiator hose is hot.
Now let’s look at the 2-valve V-8. The procedure is similar to the one described for the V-6 except there is no vent plug to worry about; all filling is done at the degas bottle. Testing procedure, first with the pressure relief cap off the degas bottle and then again with in on, is the same. Always let the engine cool between tests. The fill procedure is complete when the system is full to the mark on the degas bottle and when all tests are passed: hot air at the dash vents, normal temperature indicated on the gauge, and the upper radiator hose is hot.
Lastly, let’s look at the (Cobra) 4-valve V-8. It has a unique procedure all its own. Before I forget to mention it, the procedure I’m going to give you for the 4-valve engine is for the aluminum block version. It may not apply to the iron block supercharged Cobras. You’ll have to determine that one on your own.
One of the most important parts of the 4-valve procedure is to add ALL coolant through the vent in the cooling system bypass tube. The bypass tube is at the front of the engine and has the upper radiator hose connected to it. There’s a plug on top of the tube and that’s the location where coolant is added.
Remove the plug, remove the degas bottle cap, and add coolant into the tube until the coolant level in the degas bottle reaches the maximum mark. Replace the plug, replace the cap on the degas bottle, and run the engine until it warms up. During the test, set the heater temperature control to maximum, set the heater fan to maximum, and set the heater air discharge so that it comes out of the dash vents. To pass the test hot air must come out of the dash vents. If the test appears to be failing, stop the engine before it overheats, let the it cool, and add more coolant (50/50 premix this time) through the opening in the bypass tube. Run the engine again and test for hot air. Repeat as necessary until the test is passed. Always add any required coolant at the opening in the bypass tube.
When the test has been passed, start the engine and let it idle until its temperature stabilizes. Do this with the heater settings at maximum and air flow set to discharge through the dash vents. Check the temperature gauge to be sure it’s reading normal, make sure hot air is coming out of the dash vents, and make sure the upper radiator hose is hot. If all of these criteria are met, stop the engine and let it cool. After it’s cool, check the coolant level in the degas bottle and top it up if necessary. To do so, add 50/50 premix directly to the degas bottle.
Finally, on all engines check the cooling system for leaks. This shouldn’t be an issue if none of the hoses were disconnected and none of the other sealing points were opened up. But if your maintenance included replacement of any parts, you should check closely for leaks right away and then again after several driving cycles.