I'm getting air bubbles in my coolant overflow. They do not occur when the radiator cap is off. If you rev the engine they go away. When I bought the truck the coolant was filthy so I changed the coolant. It was properly burped. I let the truck run for more than 20 minutes with the radiator cap off, no bubbles. As soon as you put the cap on and drive the truck, the bubbles start. It does seem to use some coolant and air escapes when you open the radiator cold. No coolant in the oil or visa versa. the truck does not overheat, no strange exaust. Before I changed the coolant the temp would fluctuate to the low side, but no overheating, it did expel coolant out of the overflow, but doesn't do that after the coolant change. 1999 ranger 3.0.

 

No smoke or coolant in the oil still could mean bad head gaskets. Head gaskets get to the point where they don't quite leak yet, but let combustion pressure inter the cooling system. When the top radiator hose starts getting rock hard when it warms up, its time to change them.

 

Ok, maybe I didn't burp the system well enough or is this a symptom of something else. Tonight with the radiator cap off my son would rev the engine and hold it about 2000 rpm, the coolant level would drop. When he let it go back to idle the fluid would rise again and then burp bubbles and the level would drop back again, we did this several times adding more coolant each time. Is this a sign we didn't burp it well enough?????

 

Park on an incline and with cold engine remove cap and let it run till gets to operating temp, top off with coolant and replace cap. If you still see the bubbles then as suggested you may have head gasket issues.

 

Its sometimes difficult to burp the heater core & cooling system, especially if the thermostat doesn't have Fords air bleed valve design & or if we're trying to do it with the vehicle level. So, as has been suggested, with it at idle, heater Temp control on Max position, park the warmed up vehicle with the front end uphill, the steeper the better, so as to cause any trapped air to want to migrate toward the open thermostat, to the radiator, to be burped out. Leave the vehicle parked with the front uphill on the cool down.

You may have to do the up hill burp routine a couple of times to get a good system burp & can tell when the recovery tank level no longer drops after the engine cools.

With you saying the temp traveled to the low side, you might have a sticking open thermostat, so maybe consider changing it & while doing so, use the specified Motorcraft one, or one that'll have the air bleed valve design, to aid in air bleeding the system.

More thoughts for consideration, let us know how it goes.

 

Block tester=negative.

Pressure tested the cooling system. It does lose pressure slowly.

Ran the engine with the pressure tester on. The cooling system will not build any pressure while ideling Even after 20 minutes of running up to temp, guage will not move. When i add pressure while running...needle will not jump or shake.

Truck has yet to overheat.

Uses some coolant.

Can't find any visable leaks.

Bubbles in the overflow after driving.....bubbles stop when you rev the engine.

I'm stumped.

 

When last was the radiator cap replaced, or tested?????

 

I replaced the cap and thermostat, I even pressure tested the new one.

 

OK, do the bubbles in the recovery tank smell like exhaust???? If so & everything else checks out ok, since the coolant was in such bad shape, maybe suspect leaking head gasket/s, from neglected coolant etching away on them.

 

FYI, it was a leaking gasket. Pulled the heads. The rear left head bolts seemed really loose (compared tonthe others) The machine shop I brought the heads to said they were in very good shape, head gasket had no obvious damage....looks like the heads pulled from the block. Probably because of nasty, watery coolant. I put it back together Saturday. Truck runs great now. thanks for your input.

 

OK, good find, fix, feedback & to hear all seems well & your "on the road again"!!! Edit: Thanks for closing out your thread.

 

I don't do much work on cars any longer, but I remember now why you should never wear a wedding ring while working on anything. Damn air tools. My wife will have to live with me not wearing a ring for awhile. I'm lucky I could get the ring off. My sons thought it was hilarious though.

 

My band got bent on my finger to look like a foot ball once, it probably saved my finger, but a pair of slip joint pliers easily bent that 14k gold band back in a sorta round enough shape that I could get it off with a little bit of lube to boot!!!! Better than getting it across a high amp electrical circuit though, so I remove mine now when working on the vehicle!!!!