Coolant indigestion

My 93 Ranger XLT with 3.0 seems to suffer from coolant indigestion in the hottest part of the summer. Was checking under the hood yesterday before I left work and noticed that I couldn't see coolant down in the radiator neck. So when I got home I checked the overflow tank...none there and the radiator again after it cooled down. Added 32 oz to the overflow tank, popped the radiator cap and it took about 16-20 oz there so I put the balance in the overflow tank. Started it up, let it run until the stat opened and then shut it off. Most of the year it will show coolant in the radiator when I check, but the overflow won't show any. So what's the best use for the overflow tank...should I use it to top off the radiator...it's too weathered to be able to tell when there's something in there...or should I just keep doing what I'm doing and adding a little to the radiator when it shows to be low a bit when I check stuff under the hood? Nothing but oil on the dipstick and no bubbles in the radiator when it's running and it runs really good considering it's a 21-year-old Ford.

How often to do check levels? That coolant is going somewhere. I would pressure test the system. When cold, the radiator should be full and the recovery jug should be filled to the "cold" line. When you are loosing coolant, its either on the ground or in the engine.

Or, you're developing a head gasket leak and it's getting blown out. Of course, if that were the case, I'd expect the overflow tank to be full but it's a thought.

Also could be a cracked head or block....lots of issues for coolant leaks. Just do a leak test first. Pressure tests are the best first things to do.

Overflow tank is a bit of a misnomer(wrong name) as it sounds like if it is used something is wrong, i.e. it overflowed!!!, lol

When you heat up a fluid, like coolant(or water), it expands with temperature.

As the engine/rad coolant heats up it expands, this puts pressure in the system, rad cap is usually rated for 16psi of pressure, when the pressure in the system reaches 17psi the rad cap's large spring is pushed up and the now "extra" coolant is pushed out thru the overflow hose and into the overflow tank.
When pressure is relieved and drops to 15psi rad cap spring closes to maintain the 16psi.

The other part of this system involves the smaller spring/valve in the rad cap, yes there are TWO valves in a rad cap.
As engine cools off the coolant shrinks, when engine/rad pressure reaches -1psi the smaller spring in the rad cap is sucked open and coolant in the overflow tank is sucked back in.

For this system to work right the overflow tank must ALWAYS have coolant in it(which is why there is a COLD line on the tank), and the overflow hose must not leak.
If overflow tank is empty, then when engine cools off it will suck air into the rad instead of coolant.
It is easier to suck air than fluid, if there is a leak in the overflow hose OR anywhere in the engine/rad/hoses it will suck air from that leak point because it is easier to move the air than the coolant in the overflow tank.

If you are losing coolant slowly then you do have a leak, most likely in a place where coolant evaporates on hot parts before reaching the ground.

Best place to start is to make sure overflow system is working.
Cold engine, top up rad and fill overflow tank to COLD line, if tank level is hard to see get a straw or short stick and mark it with fluid level, put it in the cab and check fluid level the next time engine is cold, this will tell you how much coolant you are losing.

Also clean out the overflow tank next time you do a flush, any debris in the overflow tank will settle at the bottom, which is where the overflow hose is, this can block coolant from being sucked back into the rad on cool down

Expansion tank or coolant reservoir would be a more accurate term....IIRC, Ford actually calls it a 'degas bottle'.

So pressure test the radiator and start watching the coolant level in the reservoir to figure out how much it is loosing? Or are I comprehension challenged today?

sblake01 said:

Expansion tank or coolant reservoir would be a more accurate term....IIRC, Ford actually calls it a 'degas bottle'.

Click to expand...

The term degas bottle only applies if the bottle has the pressure cap, instead of the radiator.

Any other time, it's just an over flow.

tmcalavy said:

So pressure test the radiator and start watching the coolant level in the reservoir to figure out how much it is loosing? Or are I comprehension challenged today?

Click to expand...

Yes, if you want to rent a cooling system pressure tester you can pump it up to 20-25psi and watch for a leak or for pressure to slowly drop indicating a leak.

I had a leak in my overflow hose where it ran across the top of the rad, so coolant only leaked when rad was hot, and overflow hose was used, so it evaporated without me seeing the residue.
Also sucked air in so overflow tank level didn't change, lol, PITA leak

Expansion tank is used on Boilers, and is pressurized like a degas tank.

My comment was mainly about the word "overflow" sounding like something bad, but in this case it is just a name for something needed.

Checked it again today before I left work, coolant level in the radiator is fine, so is the level in the catch bucket...but the coolant looks toasty and the rubber on the stock Motorcraft cap has seen better days. Time for a new cap and a coolant flush and refill...can't remember if I did that 3 years ago when I bought this thing. Hoses looks good but I'll double check them this weekend when I'm doing the flush and refill.

Well the flush and refill went okay. Got it done after work yesterday. Pulled the overflow and windshiled wiper bottle assembly, top of the air box and intake hose and both heater hoses off the firewall. Back flushed the heater core, put the hoses back on, pulled the bottom radiator hose and let it drain. Then I flushed the block through the one heater hose, flushed the radiator real good. Buttoned it up, filled with water, let it run until the thermostat opened and everything was flowing like it should. Shut it down, pulled the bottom rad hose again and let it drain. Replaced the rad hose, and refilled it with coolant and distilled water. Whoever did this before me had their cheet together and had the hose clamps oriented for decent access...that helped a lot. Never did get the rad petcock to open up, even though I flushed it with the high-pressure garden hose attachment. Oh well, it's not that inconvenient to pull the bottom rad hose and that way is definitely faster, too. The old coolant was going south...turning muddy and brown, but still had a hint of true coolant color...and all the flushing didn't return much sludge at all, not enough to make mud in the bottom of the flush bucket anyway. Also put a new locking rad cap on it, but left the existing hoses and clamps until next time because they all looked good.

Good work

Took it down the road today, about 200+ miles round trip to pick up an antique outboard motor and stand. It is circulating coolant like it should and not spitting or using any...runs just under the N in Normal after it warms up and pegs up to the mid-gauge range after a hot restart...until you get it up to speed and down the road again. I'll call it good.

In my line of work, which is water and sewer repair, I have seen where the minerals in tap water would eat copper lines from the inside out. So I am a firm believer in distilled water in ones cooling system. By the way good job.

Heh heh, I know I'm playing with fire, but I just topped off the coolant back in '12 when I got the Rat road ready. OTOH I have put on only 4k miles since then. The needle may as well be painted on N, I'm not touching anything until that changes.