Bubbling into Coolant Overflow Tank

[Colorado Yeti]

I have a 1999 2-door Tahoe with the Vortec 350. I bought it last winter with 57,000 miles and noted oil residue in the coolant. About 2 months after I bought it, I started noticing a bubbling noise coming from the coolant overflow tank after I shut off the truck. I replaced the radiator cap bu that did not fix the problem. I then blew my heater core and knew that there was way too much pressure building up in the cooling system. I replaced the heater core & performed a compression test; all cylinders were 160-170 psi. I then replaced the intake manifold gasket with the highest quality Fel-Pro gasket kit. That fixed the problem and I didn't have any problems until this week when I noted a coolant smell after I accelerated hard. When I got home, I noted that my coolant level was kind-of low and it was bubbling again from the radiator overflow line into the coolant tank. I have not repeated a compression test and the truck is running flawlessly.

Any ideas?

 

[OR VietVet]

The bubbling may be a sign of head gasket probs but I would do a pressure test and check for pressure bleed off. You may be getting hot from low coolant level or poor flow thru the radiator. You can check with a digital thermometer for cool spots across the whole radiator surface. Has it ever shown signs of running hot? You have not said so far.

 

[Colorado Yeti]

Drives perfectly, never has overheated, doesn't smoke, never a misfire. If the compression test was normal, I would think that would rule out a head gasket / cracked cylinder head issue. Thanks for your reply.

 

[OR VietVet]

Drives perfectly, never has overheated, doesn't smoke, never a misfire. If the compression test was normal, I would think that would rule out a head gasket / cracked cylinder head issue. Thanks for your reply.

But remember, you said the compression test was ran 2 months after you bought it last winter and after the repairs you did you crossed your fingers and it was good until this week. That doesn't mean the compression may not point to a problem at this time, months later. I am so OCD I am a stickler for not assuming. Basics first then dig deeper. Great to know it is not overheating. A digital thermo would give a great reading at the thermostat housing to see if the gauge and thermo read close to the same. I drove a truck once that drove fine right up till when it did not but I may have not seen signs of what was to come like you are experiencing. I just like to get the basics out of the way first and go from there.

 

[bigfootchiro]

Definitely a potential head gasket/cracked head. My Tahoe was never overheating, and you could never feel the misfire, but I was OCD about seeing zero misfires, and couldn’t figure out why Cylinder 4 was misfiring in the slightest (on live data). Compression test came back slightly lower on Cylinder 4, and I had bubbling in the overflow tank. Pulled the heads off and there was a large crack in the valve seat.

 

[ajgreen]

NAPA has a test kit for about $40 that tests for exhaust gases in the coolant. Easy test and gives pretty definite results.

 

[glmoore0001]

Sounds like a crack or a head gasket to me also.. there is no other path for oil to get into the cooling system unless someone actually poured it in there.

 

[glmoore0001]

Unless someone made a bonehead move and poured it in the reservoir, it has to be a cracked head, block or head gasket. There is no other path for the oil and coolant to meet.

 

[Colorado Yeti]

Agreed with all above. Need to do a leak down test, not a compression test but have to buy the equipment. Are the Vortec heads prone to failure? I have never had a head failure on a standard small block and I have owned quite a few of them. Thanks everyone. I'll post an update.

 

[iCajun]

I understand mixing orange and green antifreeze looks like oil. I had an awful mess in the plastic reservoir when I bought mine. When up to temperature most everything bubbles for a few minutes after being shut down.