Disappearing coolant 2.9L

[tehutton]

Coolant seems to be disappearing from the radiator of the 1987 Ranger 2.9L my son and I rescued a few years back after a long slumber in a neighbor's yard. Oil isn't a milkshake and no visible external leaks so I'm guessing we have a slow enough head gasket leak into one of the cylinders (or a cracked head) that it's able to burn off the coolant without too much trouble -- at least for now. I plan to pull plugs and take a peek into the cylinders next week with a borescope to confirm. I'll be looking for an extremely clean top of a piston or two as well as chalky residue on plugs. In meantime, can anyone point me to how-to resources on rebuilding the 2.9 or the Cologne V-6 generally? Thinking this might the next phase of what's been a great father/son project and that it's time to start gathering parts and getting ready. Thank you, in advance, for your assistance!

 

[alwaysFlOoReD]

I've had rad leaks that couldnt be seen at the junction of the plastic side tank and the aluminum rad. Also on the rad hose itself. Another place to check is the line that runs from under the rad cap to the overflow tank. And if the rad cap isn't working some times the vacuum is lost and the fluid doesnt get pulled back into the rad.

 

[bobbywalter]

what he said. usually its a combination of all of that....they sneak out a bit at a time....then air off and pop the head. if your keeping up on the coolant its probably fine ... when its full temp and real cold out check it all then after a few hours for weeping.

 

[RonD]

+1 to above

You have an Overflow type cooling system and its pretty simple if its working
Radiator cap has two valves in it, the larger one, and then a smaller one in the center

All fluids expanded when heated
So as the engine warms up the coolant, it expands in volume, and this increases the pressure in the cooling system
Rad cap's larger valve is usually rated at 14psi, so at 15psi it spring is pushed up and warm coolant is allowed to flow out the overflow hose and to the BOTTOM of the Overflow tank, the bottom part is important
When pressure is under 14psi valve closes, but can open again if pressure goes up more
IF...........there was any air at the top of the radiator on warm up then when rad cap's valve opens the AIR will go out first, to the BOTTOM of the overflow tank, where it would bubble up to the top and its gone, overflow tank is not seal, its vented
So the overflow system is self purging of air

When engine is shut off it start to cool off, and the expanded coolant starts to shrink in volume
As it does the pressure drops down until its 0psi, now if ANY coolant or AIR was sent over to the overflow tank then pressure in radiator goes to -1psi, this pulls open the rad cap's smaller valve and sucks back in coolant from the BOTTOM of the overflow tank

So on any vehicle with an Overflow system when you remove rad cap on cold engine it should be FULL to the top, no air at all
If its not then there is a problem

As said the overflow hose can have a crack, which will leak hot coolant which evaporates very fast, and will suck in AIR instead of coolant as engine cools down

Any warm engine or radiator parts will cause hot coolant to evaporate instead of drip to the ground, so no sign of a leak, and that leak will also allow AIR to be sucked in on cool down, instead of coolant from overflow tank

There are a few test you can do to test for cracked head/head gasket issues
Easiest is to remove rad cap on COLD engine, top up rad if its low, Start engine
Watch rad cap opening
It takes 1 or 2 min for coolant to get warm enough to start expanding
So coolant should NOT start to overflow from rad cap opening for a few minutes of idling
If it starts to overflow before 2min then bummer, yes, cracked head or bad head gasket

For leaks and to test head gasket, rent a cooling system pressure tester, $10-$15 or free from some auto parts stores
It a solid rad cap with a pressure gauge and a hand pump attached
Install rad cap on cold engine
Pump up pressure to 20psi and wait and watch the gauge
If its dropping then start looking for the cold coolant dripping out, can't evaporate this time, lol

head gasket
With pressure gauge still hooked up disconnect coil wire from distributor cap or coil(or unplug coil pack on newer engines), you want a No Start
Have pressure at say 10psi
Crank the engine and watch the gauge, you will see it pulse up if there is a cracked head or blown head gasket
You can even find out which cylinder has the leak
Remove 1 spark plug at a time and crank engine again
When the pulsing stops, that last spark plug removed was from the leaking cylinder, put it back in just to be sure


Google: ford 2.9l rebuild how-to

Lots of advice and spec out there

 

[tehutton]

Thanks to all and particularly to RonD for his thorough response. I'd love for it to be as simple as a cracked overflow hose and can borrow a pressure tester from AZ for free.