300 Six Coolant Flush?

[Nathan Plemons]

I have a 95 F-150, 2WD. I changed the belt on my truck the other day and while I was under the hood I looked at the coolant, it was rather nasty ugly brown. I got to thinking that in the 8 years and 80,000 miles that I've owned the truck, the coolant has never been touched. I'd say the previous owner didn't either, so really I've probably got coolant that dates back to 95 and has 177k miles on it. Obviously this isn't a good thing. I want to flush the coolant completely, not just the radiator. I was thinking about getting one of those coolant flush kits, splicing it into the heater hose, and back flushing the system. I was hoping though, that after this was done I could drain the block so I could start from scratch with a fresh, proper coolant and water mixture. I have not been able to find information about a drain on the block for the 300. My Haynes manual shows a picture for the V8. Alldata doesn't list anything for the 300 either. Does anybody know if the 300 even has a drain on the block? Thanks.

[masseyman]

I think the 300 does have a drain plug, but I never found it on my '88 F-150. I wouldn't even mess with the drain plug, if you flush the system you should get most of the crud out anyway. Then just drain the radiator and add anti-freeze when done flushing. You may not get the anti-freeze mixture quite strong enough that way, and may have to drain the radiator partially again and strengten the anti-freeze, thus wasting some anti-freeze, that's what I do. When I install the flushing T, I just unhook the heater hose at the engine end and take another short piece of heater hose to hook temporarily to the engine end. That way when I'm done, I don't have that plastic T in there to possibly break. I guess at this point you may want to install some new heater and radiator hoses anyway.

[glc]

Put a new thermostat in there while you are at it - on general principles.

Using a flushing tee, there is a way to force a full antifreeze load in after a complete flush - you leave the cap off the tee when filling the radiator, when it fills up, plain water will start coming out the tee before you see coolant. Put the cap back on the tee when you have the desired amount of antifreeze in there.

[Nathan Plemons]

Come to think of it, I wasn't entirely accurate. Shortly after my dad bought the truck he did replace the thermostat, thinking that was a potential problem with the heater. I know he didn't flush or change the coolant though, he just replaced whatever was lost in the process, which likely wasn't much.

Being said, at 8 years old now, and less than $10, it's not a bad idea to change it again.

[glc]

I replace the thermostat every time I drain/refill and/or flush the system - again, on general principle.

[RaWarrior]

Be prepared for a mess, the crappy plastic drain valves tend to bust from sitting for years without being used. Mine was seized closed and I had to unscrew the handle all the way and let it barf out of there, it went everywhere and made a huge mess.

Using an off-the-shelf flush fluid can have good results, that's what I did and the coolant in mine was pretty nasty. Drain the old coolant, fill almost all the way with plain water, then add the flush fluid. Drive it around for a few minutes(mine didn't overheat, but it was rather close to the H mark). Let it cool a bit and drain the water/flush mix. I refilled with a 50/50 coolant mix, drove it to work the next day, then drained/refilled again since the coolant was at best a dirty,pale green. Now it's bright green and it runs a lot cooler than it used to.

[Nathan Plemons]

Alright, the other day the weather was perfect so I went to the store and got 2 gallons of coolant, prestone backflush kit, prestone radiator flush fluid.

I didn't have any trouble opening the drain on the radiator. I let it drain and then put the flush stuff in there and topped it off with water. It didn't seem like it took that much, perhaps the radiator drain **** was just stopped up with crap, the old coolant looked like dirty dexcool, even though I know it used to be green!

I ran the engine up to operating temp and drained the radiator again. I then used the backflush kit to clear out the heater core and hopefully the block. I ran it this way until the water coming out of the radiator appeared clear.

I drained the radiator again and then started adding coolant to the radiator, leaving the backflush port open. Sure enough I was able to get the proper amount of coolant added and lost mostly just water through the open backflush port. I capped off the port, filled up the surge tank (which I had flushed thoroughly, it was NASTY as well.) I drove the truck around the block and didn't notice any problems at all.

The only trouble of the entire process was that the hose clamp going from the radiator to the surge tank decided to disintegrate as soon as I touched it. I figure it'll stay on there as a friction fit until I can get a replacement.

I drove the truck to work for the first time today since the flush and I noticed that my coolant gauge seems to be a lot more active. Normally if the engine was cold I would notice that the coolant temp would go up to between the "R" and "M" on NORMAL before it would fall back down around to the O. I assumed this was just the thermostat opening.

Today I noticed that it got to near the "M" and "A" before it dropped. This is still well out of the danger zone, just hotter than usual. When it did drop, it dropped to it's usual spot around the O. I noticed that at a traffic light the temps would start to creep higher than usual, but still no more than the lower part of R. The second I would give it any gas at all it would drop, too quick for it to be airflow through the radiator helping.

I have two theories:

1. I might have some air in the system that hasn't worked itself out yet.
2. The old coolant was so nasty that it wasn't doing a very good job of absorbing or losing heat quickly, thus causing the gauge to respond slowly.

Thoughts?

[glc]

1. Quite possible.
2. You should have changed the thermostat.

[adrianspeeder]

The stock lie'o'meter doesn't tell you much anyway. I run an aftermarket temp sender and gauge with actual temperature markings.

Adrianspeeder