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Hello Everyone,
I have long "suffered" from my 940 Turbo being unable to burp a small/moderate amount of air out of the heater core.
Whenever the engine is started for the first time, there is a distinct gurgling sound from behind the dash, clearly from the heater core.
All the rudimentary bleeding methods have been employed, and proper refilling procedures adhered to at change over times. There are no leaks of the G-48 coolant whatsoever in the entire system, and it is filled to the proper level. The water valve is OEM brass and functions as designed, and the heater always blows hot, which is further evidenced by both heater hoses being hot to the touch when at operating temperature.
I even purchased a Maddox MH-1B Cooling System Test & Refill Kit from dear Harbor Freight and gently pulled down the system until the hoses collapsed, wherein the negative vacuum held for 5 minutes. But alas, after that procedure, the same sound comes at start-up from the heater core.
What am I missing?
I would appreciate and advice or direction.
John
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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At the risk of sounding stupid, doesn't the thermostat have a little jiggle valve that when installed almost? up allows the system to bleed air
I just copied this fr the FAQ's
Thermostats must be installed with the small venting nipple oriented upward. If incorrectly installed,Thermostat and O-Ring an air pocket will form in the thermostat housing causing a reduction of cooling abilities. When you replace coolant, loosen the thermostat housing when refilling and bleed air from the system until the coolant appears at the thermostat, just to make sure you have no air bubbles.
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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Hi I don’t know much about the 900 or even the AWD cars but to me it sounds like a place where water has collected.
In my past refrigeration career it’s common for it to happen in evaporators.
Maybe the AC and the HEATER core plenum is not draining itself of its condensations.
The air conditioning comes on in defrost mode on newer cars automatically.
Maybe if you felt around under the car for the duck bill rubber drain hose you can give it a squeeze.
It’s very possible that leaves or algae has gotten it plugged up.
When the fan runs, even at its lowest speed by default, it can whip up the water and muck.
You might try pulling the fuse to the fan to stop that idea.
This duck bill I’m speaking about usually drips right onto the transmission. The duck bill fits down through the body of the car on the 240s as I remember and can be reached from under the catch pan inside the car.
Or it is from above the transmission.
Been a long time since I have been under my dash for AC issues.
I hope it stays that way.
Phil
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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Dear Townshend,
Hope you're well and stay so! You wrote, "All the rudimentary bleeding methods have been employed...".
Does this include parking on a steep incline (e.g., a hill) and allowing engine to idle for, say, 10 minutes (nose towards hill's summit and then another 10 minutes with the tail towards hill's summit)?
I ask, because this method usually allows all air to exit cooling system, after the replacement of coolant, water pump, heater hoses, or rad hoses replacement.
Hope this helps.
Yours faithfully,
Spook
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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Such gurgling is normal in the AC system as the charge becomes low. In winter weather like now, you're probably using the defrost setting which tries to activate the AC compressor as long as there is a minimal amount of refrigerant to trigger the low pressure pressostat. The gurgling you're hearing is likely in the evaporator core next to the heater core. Disconnect the AC compressor at the drier connector and I'm fairly confident your gurgling will go away.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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Hi Dave.
Nice to hear from you again with your always prompt replies.
This gurgling sound is definitely coolant, not freon related. The A/C gives it share of hissing sounds at the orifice tube (ha!) at times during compressor cycling.
It's just there is a darn pocket of air in the heater core somewhere, and I'd like to know how to burp it out.
Tried all the driving with the heater on high temperature and the reservoir cap loosened. I really thought putting 20g vacuum on the system would draw it out too, but no such luck.
Nonetheless, I thank you for your kind reply and will talk to you again.
Regards,
John
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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If you really feel you need to burp the heater core then you might want to think about removing the expansion tank cap, setting the heater control on high, fully warming the car until the thermostat is open and hot coolant flows in the upper rad hose (don't worry, there should be no boil over even after 15-20 minutes of idling), then massaging the lower rad heater hose to force fluid and any trapped air through the coolant system and heater core and out the upper heater core nipple. I'll often massage the upper and lower rad hoses together in opposition to flush coolant back and forth through the block to move trapped air.
Maybe try doing this with the car parked or jackup up with the right side of the car high. The upper heater core nipple goes across the top of the heater core and connects to the upper right side as I recall, so any trapped air in the upper part of the core should now be in the upper heater hose and hopefully now be able to work its way back to the water pump on the return line behind the block.
I've not had such gurgling sounds in the heater core. Any chance your heater control valve is failing and somehow unusually restricting cooolant flow to make for an unusual sound? Also check that the small vacuum hose that connects to the heater control nipple isn't split or melted closer to the valve.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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Hi Dave.
I wanted to tell you I finally found the source of the unending gurgling from the heater core under the dash.
Turns out I had the heater hoses reversed. It was flowing backwards.
Happened during the engine rebuild couple of years ago.
Thought you'd like to know. Funny problem. Basic solution.
Now I posted a new inquiry on the oil pan mounting bolts. Need torque values.
Thanks for all your kind help Dave.
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posted by
someone claiming to be
on
Wed Dec 31 18:00 CST 1969 [ RELATED]
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Ah, that makes sense and first time I've heard of that. Coolant running down from the top of the core and out the bottom won't push out all the air, so it gurgles. It's not that hard to get the heater hoses swtiched on the lower and upper nipples on the firewall. Perhaps even easier if you're putting in new hoses. Some aftermarket inlet heater hoses come as one piece and you cut it to insert the heater valve, so when you size it for the cut you'd better be doing it to the lower nipple. If you'd reverse flushed the system it would have pushed out the air, but the heater would have run less efficiently. People used to reverse flush, installing a hose fitting in the upper heater hose (Prestone sometimes came with that fitting as a promo or you could buy it separately). I did that on my 140, but not since. Hose flushing leaves too much tap water in the system after the final drain, while de-ionized water or pre-mixed coolant is what should be used. I no longer flush unless I see a lot of crud in the original draining. Too much flushing can remove scale that is actualling lining the system and protecting the metal. Many people, including me, will experience waterpump and core failures within a few weeks or month of a coolant change. They were going to go eventiually, just maybe not so soon.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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