OMG!!! Bubbles!

I drive a '91 Plymouth Sundance RS 2.5 4 cyl w/ 205,000 miles (30,000
miles on used junkyard engine).

Ok, I was coming home from school today. When I parked into my
driveway, I decided to leave engine running. I opened the hood and
decided to, out of curiousity, check my coolant while the engine was
on. Well, you know the common saying: "Go Looking For Trouble, And
You're Bound To Find It!!! I took the lid off the overflow bottle for
the engine coolant, and you know what I saw? Bubbles! That's right, a
steady flow of bubbles coming up through there!

Is this anything to take seriously? Does this mean that my head gasket
is going bad again?

Or could it be something relatively simple? I sure hope so... ;-D

Engine doesn't overheat at all. It runs really cool (slightly past 2nd
mark over C, or 1/4 mark, when driving) even in 95 Degree weather. I
use a 180 Degree Thermostat. Fan comes on at center of the gauge. There
are no wild temperature gauge fluctuations either, and it stays pretty
stable. I never have to add coolant at all even after long trips, so
there's not coolant loss or leaks. The coolant in overflow puke tank
stays between MIN and MAX when cold and goes to MAX when temp gauge
gets to the center by when the fan kicks on. I had the head gasket
replaced last December about 10,000 miles ago and a valve job done as
well. Right after that, I replaced the radiator, radiator cap, hoses,
and thermostat. Recently, I had water pump/alt belt replaced, too.

 

Since you mention that the head gasket was replaced, we should be able
to rule that out. It could be air in the system, but I am not sure if
it would act like that. I would suggest trying to bleed the air out.
There is a plug in the thermostat housing for this purpose.

When the headgasket failed on my 2.5, coolant would be forced into the
recovery tank, until the system was low on coolant.

-Kirk Matheson

 

Or it could be that since he un-corked an already hot system, pockets of
coolant flashed to steam immediately when the pressure was released
causing a flow of "bubbles" through the overflow. If it 'bubbles' with
the engine COLD, then it might be a real problem. If its running cool
and not losing coolant, leave the cap on when the engine's hot and
monitor the coolant level carefully over a few weeks.

 

I tried to bleed the air (just to make sure) by taking the hex screw
off of the top of the thermostat housing. But. I was unable to get the
screw out because it seemed stuck. Instead, I put car on incline,
opened radiator cap and let engine run with it off until the air
bubbles were gone. No help.

I notice that the patterns of the bubbles in the overflow go like this:

The bubbles seem to come only when the gauge gets almost to halfway.
Then the fan comes on. Right after the fan comes one, the bubbles go
away. Why is that?

 

Put a combustion gas sniffer on it.

 

I did "not" touch that radiator cap while the system was hot and engine
running! The cap I opened to check coolant was the one for the plastic
overflow bottle (recovery tank marked with MIN and MAX).

Anyway, I don't get bubbles at all while the engine is COLD. They don't
occur until the gauge gets close to the center. When the fan kicks on
(which is at the center of the gauge), the bubbles go away within a few
seconds and don't come back until the gauge gets to the halfway mark
again.

 

I'm wondering if you have the correct mix of antifreeze and water. Even if
you live in a warm climate you still need to run a 50/50 mix of water and
antifreeze. The antifreeze also provides lubrication for the water pump.

Another possibility is the radiator cap is not maintaining pressure.

HTH
Gyz

 

Yes, It's the correct 50/50 water:antifreeze ratio. The coolant has
been in there for only 9 months since I installed the new radiator in
Jan 2005. I just used one of the random radiator caps I had laying
around (which was pretty new, I think). I tried different radiator caps
at the time of the head gasket failure last year to try to solve the
problem of the puking coolant from overflow bottle (which later turned
out to be caused by blowd head gasket). I do have the right pressure
rating cap: 16 Pounds which my car calls for

 

The only sure way to see if you are having a failure on you head gasket is
take you car to a shop and ask kindly if they take their emission tester and
take a sniff in the radiator. The tester will clearly show them if you have
any exhaust or hyrdrocarbon appearing in your coolant.

SCOTT

 

In that case, you need a new radiator pressure cap. Its not holding the
full system pressure, and is allowing coolant/vapor to escape into the
overflow bottle when the engine's hot.