I actually did do some research in past threads and on the web before asking this question and I didn't find the answer, maybe I missed it somewhere. I see that it's common for heads to crack on the 3.0 and for "aquarium style" coolant bubbles to develop. If the coolant bubbles develop nearly immediately after the truck is started (thermostat closed, upper radiator hose cold), wouldn't that indicate a leak somewhere other than a cylinder/head gasket? Somewhere that would admit air but not cause a coolant leak?

A little background, a good friend of mine has a 2000 Ranger 4WD 3.0 automatic with 133k miles he wants to trade for a vehicle I have. His grandfather had it for a long time and he bought it 5 years ago with 102,000 miles. He's taken good care of it but no longer uses it. He put a water pump, thermostat, and new radiator cap some time ago. It runs just fine, no CEL light, but when he dropped it off, I heard and saw the aquarium bubbles in the coolant tank and I just want to be sure about this cold versus hot question.

I've had maybe a half dozen Rangers going back to an 87 2.3 I bought new but I've never had any with the 3.0 V6 so I don't know anything about it.

The temp gauge on this one is just below halfway versus the much lower position of the 2.3 and 2,0 trucks I've owned but he said it's always been that way. Maybe that's normal for the 3.0, it stays stable and that's what I usually look for, in addition to being below halfway.

I might have had that engine in the Probe I bought new in 1990 or one of the Taurii I owned over the years, but I don't recall any problems with any of them or where the temp gauge ran.

I would suspect the cap but it appears to be new and it's marked with a 1.1, which I assume is 1.1 bar or 15.95 PSI? I have no problem buying another one as a test if you guys think that's worth a shot.

I have a day or two to make a decision on the trade and we are both okay with giving the vehicles back. I'm not going to do any invasive tests on the truck because it's not mine but I would appreciate any information you guys have on the hot versus cold bubbling question or any other input on the situation.

I'd like to make something of the truck, but I don't have room for another project. I already have two of those, haha.

Thanks

 

PS

- there is no reported loss of coolant, either.

- if these were combustion chamber bubbles, wouldn't a food thermometer reading the bubbles in otherwise cold coolant from a cold start read a much higher temperature? I've seen in other posts that the factory stats had what are called jiggle pins on the Cummins truck. Little valves to allow air to purge during filling and allow some warm coolant past the stat and into the circuit to heat more evenly. Wonder if the bubbles from cold start could be getting past the jiggle pins?

 

A leak in the engine/rad part of the cooling system would only pull air in while engine was off and cooling down from operating temp.

The self purging system used on most vehicles works like this.
Assuming cold engine and coolant at the top of radiator.

When you start the engine the water pump circulates coolant thru the system, it doesn't increase pressure in the system it is just a circulation pump.
Radiator hoses are larger and so most of the flow would go there but if thermostat is closed then flow is thru the by-pass hoses, heater hoses usually.
Yes, thermostats often have a jiggle valve(small hole with metal pin in it) that should be placed at the 12:00 position when installing thermostat, this is to let air out if any should get in to upper part of engine.

As the coolant warms up it will expand in volume, like all fluids, this is what creates the pressure in the system, this takes about 5 minutes at least, usually 10-15min.
Radiator cap holds in that pressure to give the coolant a higher boiling point.
Radiator caps have TWO valves inside
Pressure valve is the larger one with the big spring, usually rated at 14psi
When coolant heats up enough pressure in the system will reach 15psi which pushes open the radiator caps large valve and warm coolant flows to the overflow tank via the overflow hose.
If there was air in the system it would usually collect at the radiator cap opening which would cause bubbles in the overflow tank as it was purged.

After engine is shut off and starts to cool down, the coolant volume shrinks, so pressure in the system drops, when pressure reaches -1psi the small valve in the center of the radiator cap is pulled open and coolant is sucked back into the radiator from the overflow tank.
So all air would be purged at this time, it bubbled up and out of the overflow tank, only coolant can be sucked back in, this is why the overflow tank is build the way it is.

Air is easier to suck in than coolant, so if there were any leaks in the system, including the overflow hose, then as the engine cooled down air would be sucked in instead of coolant.



To check if system is working top up cold rad.
Drive vehicle for at least 15 minutes then shut it off and let it cool down all the way
Open rad cap, there should be coolant right at the top, no air at all.
If there is air then something is wrong.

A bad head gasket or cracked head will pressurize the cooling system very fast.
So cold engine, top up rad and put cap on, start engine, run it for 2 or 3 minutes then shut it off.
Open rad cap SLOWLY, if there is pressure then you have a bad gasket or cracked head.

The 2.9l and 4.0l OHV engines had weak castings that caused them to crack between valve seats, 3.0l didn't have that flaw, but they can be cracked like any head if overheated enough.

Overheating an engine(any engine) causes the metal in the head to expand more than normal, which can cause a crack in the metal, but what is more common is that the head gasket gets crushed as the head metal expands.
Head is held in place by the head bolts so when the metal starts to expand it presses harder against the block, which is also expanding a bit more, this puts the head gasket between the proverbial "Rock and a hard place", lol.

This is why it is very important to pull over at the first sign of overheating in any vehicle.
Never try to "make it home", let engine cool down and see what problem might be.
If you let it cool down and then drive for 10 minutes, let it cool down and drive if for 10 minutes, you will make more money per hour than you ever have.
i.e. a $10 heater hose repair, cause for overheating, and 4 hours of your time "limping home"
Or $10 heater hose and $600-$1,200 to replace gaskets and maybe heads but you saved 4 hours in cool downs.

$300 bucks an hour out of your pocket or IN your pocket

 

Thank you for the detailed reply. This should be more than enough to find out what is going on.

 

2 to 3 minutes of run time and no pressure at the radiator cap. Anything more than that, and the upper hose begins to get hot and the system gets pressurized. It must have the jiggle pin because this happens well before the gauge gets anywhere close to the usual upper range of travel with the thermostat open

Not being familiar with Rangers, I didn't know where the reservoir levels were. After I got my glasses and discovered the FULL COLD line was above the level of the coolant by maybe an inch to an inch and a half, I filled it to that FULL COLD line.

After that, there was no more bubbling with the truck running or after it had been turned off when fully hot (upper hose and gauge stable at highest point), which is what I saw previously.

I'm going to wait till it cools down and repeat the test and see if it does the same again.

 

Yes, with low overflow tank level you could have been sucking some air back in when it cooled down fully.

I use tape on the outside of the overflow tank, my eyes are not the best, and the darn writing on those tanks is hard to see

 

I checked the truck last night with a brief startup and there were no bubbles present. I drove it approximately 35 miles to work this morning and there were no bubbles when the truck was idling after I got there, but once I shut it off, a series of small bubbles appeared in the coolant above the hose in that front corner that tapered off after approximately a minute.

Temp gauge was steady throughout the drive. Coolant level in the radiator and overflow cold looked to be about the same.

However....

There is a pretty good leak from what appears to be the rear main seal.

It feels like the rear axle is shifting on straightline takeoff from a stop. Rear shackles were replaced because they broke (apparently not uncommon?) but something is moving or has play. I get a little clunk out of the rear end when I move the driveshaft radially and it does not appear to be the U joint. With 133k miles, it seems a little early for wear but I don't know Rangers so maybe not.

Has the typical door ajar problems so the dome light is taken apart, i see elsewhere there is a sensor fix for that.

Lots of rust underneath, nothing perforated but lots of scale.

It runs well and I like it but all things considered, it's more problems than I want to take on and I'm going to send it back.

Thanks for the input!

 

When you shut off an engine after driving it awhile you shut off coolant circulation and cooling, i.e. water pump and fan are shut off.
There can be hot spots in the head that causes the now not moving coolant to boil in that one spot, that makes the bubbles and increases the pressure in the system, the bubbles travel to the high spot, thermostat is open, which is rad cap, and because of the higher pressure you see those bubbles being pushed out to the overflow tank.

Make sure you are running 50/50 water/coolant, too much coolant lowers freezing point but also lowers boiling point.
And next time you change the coolant, every 2 years, do a good flush, the bubbling often means cooling system is not working at 100%, instead of running at normal 200degF engine may be running at 210degF, which is fine but when you shut it off that extra 10deg is allowing coolant to reach boiling point in the head, which makes the bubbles.

Another reason can be the road, if you drive up a long hill and then park and shut off the engine, it will be hotter after climbing the hill, so you get the bubbles.


Rear main seal leaks are not typical with the 3.0l, can happen of course just not a common issue.

The door open/closed sensor is in the door latch on the door side, often spraying WD40 into the latch will allow it to move again and show door closed when it is.

Google: Ranger door ajar

 

Thanks for the reply and information.

I also found a thread about removing the switches on the door latches so allow them to read closed all of the time and eliminate the door ajar fault.

The big showstopper on this truck is the rear end moving around. I have two or three other projects at the moment so I can't take on another one right now.

The amount of rust is a close second on the showstopper list. Everything has a lot of scale rust on it and perforation can't be far behind, if its not already hiding somewhere.