Air getting in cooling system?

[Mounty99]

Hello all.

Recently had heater core replaced in my 1999 Mountaineer 5.0. Heater working great, but noticed now getting bubbles in coolant reservoir after shutting off engine. But it is NOT overheating. Have a ScanGuage2 and coolant temp steady at 190/191 degrees when driving.

Thought was just air in the system, but have burped this thing multiple times (using proper procedure)...and can't seem to fix it. When I burp, I get some bubbles, but then never any suction back into the system. Car also seems to have a rougher idle, maybe a small occasional "knock"?....that was not there before.

Put a new radiator cap on it, and burped again today. But still something still is not right. Again, new radiator cap. Thermostat definitely opening and closing. No signs that it would be a head gasket, and sure hoping it is not!

Not sure how to proceed? Any suggestions would be much appreciated.

 

[MrQ]

Umm, has this engine been overheated at any point?

 

[Mounty99]

Umm, has this engine been overheated at any point?

No, has never been overheated.

 

[1998Exp]

Check for exhaust gas in the coolant. If you don't know how, there are several videos on youtube.

 

[rasouth]

When the engine is cold remove radiator cap and start engine. Does the coolant level change? Bubble over? If it does you might have a head gasket leak.

 

[Runnin'OnEmpty]

I too suspect you have a head gasket leak.
If so, small bubbles will show in the coolant overflow bottle,
and there'll be a 'sooty' residue (while at idle).
You can pull and examine the plugs to find which cylinder
is affected. The leaky one will show a lighter colored and
cleaner plug than the rest.

 

[rasouth]

A compression test would help in finding the cylinder that is affected, if there is a problem with the head or gasket.
You could have a small leak in the upper part of your radiator, but then you would see signs of leaking or residue in your engine.

 

[J_C]

I too, suspect a head gasket leak. We don't know what condition it is in (subjective value of vehicle at 257K mi.) or your ability to pull the heads, then see if just a gasket (probably) or a warp or cracked head, versus putting some stop leak in and seeing if that helps.

At this mileage I would be hesitant to do the head gaskets. I mean it's a little help, late in the lifespan? I'd put stop leak in hoping it does the trick to give me time to weigh the options and come to terms with the idea that it may be time to either retire it or swap the whole engine. If it is low rust then I would seriously consider swapping the engine unless you just want to move on to something else.

 

[94Eddie]

Replacing head gaskets on a 5.0L is easy. I can do it on my '89 LX 5.0L Mustang in about 1.5 hours taking my time. I know because running 16 psi of boost on it had me doing this regularly. If the vehicle is in good overall condition there is no need to dump it due to a head gasket issue. Especially if no coolant got into the oil.

 

[C420sailor]

I wouldn’t hesitate to do engine work on a trucklet that clean. Wow.

 

[MrQ]

Head gaskets aren't too bad. Took me and my friend about 4-5 hours on one side, but that truck had some rust on it. Should be able to do it in a couple of days without too much trouble. Be careful of the front two lower intake bolts that go into the head however, they do have a tendency to corrode and snap (I'd head by the junkyard and grab a few of the other ones out of another 96-01 V8). Personally would just buy some rebuilt GT40P heads and put them on at the same time. About $700 all told (they are relatively inexpensive) Might want to throw in some new lifters and pushrods. About a grand all told with new head bolts and she'll run like new.

 

[Mounty99]

Took the Merc in for a quick pressure test. Said there was a small leak around the water pump. Maybe got whacked when changing out heater core? I haven't lost a drop of coolant though.

So would that small leak be the source of those bubbles?

 

[94Eddie]

You can get a kit to test for exhaust gasses coming in contact with the coolant. This is one way to tell if it is a head gasket problem. Also, many shops can do this test for you.

 

[MrQ]

Took the Merc in for a quick pressure test. Said there was a small leak around the water pump. Maybe got whacked when changing out heater core? I haven't lost a drop of coolant though.

So would that small leak be the source of those bubbles?

I have had my share of leaky water pumps and I have not seen air bubbles get created in a system because of that. Pressure and coolant loss yes. However it sounds like something is ADDING pressure to the system, thus the bubbles. This points to our concern with it being a head gasket issue.

 

[RickOTR]

Blown head gaskets were common place for these engines when they were used in the Mustang GTs. That's why Ford came out with the 4.6

 

[Mounty99]

Ok, so I ordered a block tester that should be arriving tonight. Will test for exhaust gases and report back.

Here's an interesting side story. Like a said, took the Merc in for pressure test few days back. Have driven about 60 miles since picking up truck. Went out this morning, looked under the hood, and.....no radiator cap!! Completely gone. Guess the shop forgot to put it back on after pressure test?

I didn't even know it would drive like that without overheating. ScanGuage2 showed coolant temp staying at 190 degrees for the entire time sans cap. Just ordered a new cap (thanks amazon prime) that should be here today.

Thanks again for all the help/suggestions.