I'll try and be brief. Have a '91 740 that wasn't heating the cabin AND was overheating. Replaced the heater core (yes there was a hole in it). Also replaced a valve/sensor of some type that passes hot water into the core (yes it needed to be replaced -- it had completely degraded). This worked and restored heat, without a doubt. Very soon thereafter also noted that it was continuing to overheat and lose coolant. Replaced the thermostat (yes it was original). This fixed the overheating problem, the coolant loss problem, and restored heat to the cabin yet again. I was happy.

Then, in the last couple of days, I've now noted that the heat in the cabin has again faded. If the temperature control is all the way over on "cold", it blows cold air (it's winter here). If it's over on "hot", it blows just very marginally warmer air. We're talking marginally. I can hear the box "working" to change from cold to hot and vice versa when I turn the dial.

I'm at a loss as to what might be going on now. Some "hang up" in the distributor box? Punctured vacuum hose? Clog in the water line going into the heater core?

I really don't want to tear the dash back down just to figure out what is going on. Any thoughts??

Thanks!

 

Well, a little more development -- so maybe someone can help me just crystallize my understanding here. I had a gut feeling that maybe there IS something to "burping the system." So I took the top off the overflow tank -- when I did so bubbles rolled up, for starters. Then I started the car -- and very quickly the level in the tank dropped to essentially zero -- there was just a very little fluid left in the very bottom of the overflow tank. It warmed up. The TEMPERATURE gauge never got over halfway to hot -- the upper radiator hose got hot, etc., but no signs of overheating, per se. But still no true cabin heat. So I slowly trickled in some coolant -- and watched it continue to basically drain straight through into the system. After doing this a few times, the overflow tank finally started to "back up" and retain some fluid. Then re-checked the cabin heat -- and voila! -- heat in the cabin.

So it SEEMS there was air in the system. Now can someone kind of clarify for me just exactly what was going on? Air trapped in the system which basically didn't allow the heater core to fully fill with hot water?? Am I anywhere near the right answer? And is it possible for air to continue to get drawn into the system somehow? Could this POSSIBLY be a bad head gasket? What the big/bad/ugly signs of a bad head gasket?

Thanks in advance. . .

 

1. yes on the aluminum block engines (1991+) not a problem on the red block engines

2. yes due to a leak

3. you have a loss of coolant

4. yes

5. coolant loss, overheating, poor starting (coolant on spark plug) It would be extremely rare for almost any Volvo to mix coolant with oil with a damaged head gasket - other cars - yes - Volvo - no. The damaged head gasket could be allowing the combustion gases to be pumped into the coolant - what does it smell like in the coolant Bottle? A extremely damaged gasket will create air bubbles that float out of the coolant bottle with the cap off and the engine running.

If the engine has been overheated (i'm sure it has during the x years alive, and many cooling system failures) you could easily have a damaged head gasket - If you are prone to think in this direction - The only head gasket in a can I've had success with is K-Seal poured directly into the head after thermostat removal. I used this product successfully several times only on a 960 engine - they would leak coolant externally from the right rear corner of the head when cold.

 

"Aluminum block 1991+"? Aren't ALL Volvo b230/f Red Blocks?
Volvo Red Blocks can develop air bubbles.
And, yes, you have the signs of bad head gasket.
If you want a cheap fix-in-a-bottle I have had excellent results with Blue Devil brand, not the Pour N Go but the full strength stuff. They guarantee the results.
Head gaskets can be tricky and they don't fail the same way: they isolate compression, from oil, from coolant. There can be several combinations among the three. The compression (air) being forced into the cooling system is the hardest to cure with additives, coolant in the oil the easiest.

 

I have been running with a leaking head gasket for about the last 100k miles. I've not seen this type of leak as it is an external oil leak and not a coolant leak. It is on the exhaust side between #1 and #2 cylinders. I lose about a quart of oil every 1500 miles so I have been waiting for it to blow. I'm still trying to get to 500k miles and so far only at 395k. Having just got a new car I'll settle for 400k and then figure out what to do.

 

yeah, external leaks are very common with higher miles, and you can go a long time with nothing more than that-- no engine running issues. of course eventually, if you don't want leaks, you gotta change the HG...

 

Just a little more info. . .went and did some more investigation. Can't see any evidence of coolant mixing with oil -- no foam or residue on the cap or the dipstick. No real residue in the overflow tank when I looked. A couple of things about the coolant tank, though -- it was wise to tell me to sniff the tank. When I did so last night, I wasn't really sure what I was sniffing FOR -- but when I did, the prevailing, predominant odor wasn't coolant, and it wasn't what I would think was oil. It took me a second to isolate what it was, because it wasn't overwhelming, but if you had to ask me, yes, it would be the faint smell of exhaust gases. I started to car up this morning and watched the overflow tank closely -- I didn't see any immediate, persistent signs of bubbling up into the fluid. It maintained for a while -- and then I could see fluid actually flowing back into the tank (as the thermostat opened, I suppose). Then after a few more minutes, the level quickly dropped, but again, without any real persistent "bubbling", other than what seems to happen when fluid is flowing down a drain. Again, I imagine this is the "siphoning" action of the fluid being drawn out of the tank into the system. So that's where I ended up. I let it cool for a while and then proceeded with adding a bottle of K-seal to the system as directed by the manufacturer.

So really, at this point, I want to kind of understand what I seem to be dealing with (theoretically). If I'm dealing with a faulty head gasket, essentially, at the "down stroke" of the cylinder, it's drawing small amounts of coolant past the gasket into the combustion chambers, and on the exhaust stroke, small levels of gases are being forced through the gasket back into the coolant, correct? In thinking back now, the cooling system seemed to be pressurized for HOURS after stopping the car. If I went out hours later and uncapped the overflow tank, there would still be an escape of "air" -- not the "usual" you would expect or see simply from hot coolant, if that makes sense.

Thanks for your input. I have a rudimentary understanding of how an internal combustion engine works, but I'm wondering if my understanding is basically correct.

 

Yes all 240/740/940 b21/23/230 have cast iron blocks. The 1991+ dohc 960 6 cyl, 1993+ 850+ 5 cylinder, s40 4 cylinder engines are more reluctant to bleed air out, they require more time and usually driving to get all the air out. The b21/23/230 take less lime - that's what I was referring to.

Volvos very rarely mix oil with coolant or coolant with oil. People do find grey goo on their dipsticks and oil caps - that comes from condensation and short trips/open thermostat never boiling off the condensation in the crankcase. Have seen that hundreds of times, mostly freaked out customers who think or have been told they have a blown head gasket when checking or adding oil - and don't.

That odor is from the combustion chamber gasses - you have a badly blown head gasket if you can smell it.

Hopefully you put the k-seal into the head with the thermostat removed. (which is not their directions and either way won't help at this point) If you pour it into the coolant bottle - very little will end up where you want it - first it drops into the middle of the radiator and it won't circulate into the head until the thermostat opens. If you pour it directly into the head it immediately circulates through the head and block and stays in there until the thermostat opens.

Yes you have a badly blown head gasket, causing the extreme pressure, the smell, and I would not recommend driving the car until fixed. The combustion gases are displacing the coolant around the combustion chambers - that will overheat internal parts of the engine badly if no coolant is touching. More than likely the head will be warped - Heads warp on both the top and the bottom, so if you simply resurface the head face to be flat - the cam side will still be warped and will cause the cam to bind. If warped more than a few thousands the head will need to be straightened to do the job correctly. A valve job will be required after straightening.