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Discussion Starter #1
I've been having some issues with my 2001 Aero wagon of late. Every now and then (usually in heavy traffic), I would have boiling/bubbling sounds coming from the expansion tank, followed shortly thereafter by plumes of steam coming from the expansion tank cap/valve through the bonnet. I quickly pull over and find a substantial amount of liquid coolant has exploded out the expansion tank cap and is all over the expansion tank side of the engine bay, as well as on the road.

About 3 weeks ago I purchased a new cam cover gasket and new head bolts, and completed the head retorque procedure following the factory torque and sequencing specifications. At the same time, I removed and tested the thermostat (functions well), and did a flush of the coolant system. The car has driven perfectly for the last 3 weeks, with the coolant level in the expansion tank remaining constant, with no signs of any issues whatsoever.

On the weekend just gone however, the exact same thing happened. I was sitting in traffic, heard the boiling, immediately pulled over, and was met with a cloud of steam coming out the bonnet, and liquid coolant all over the road.

Here's the interesting thing however. Since doing the head retorque, my coolant temperature sensor has been all over the place. The temperature gauge in the dash will sit at 'normal' temperature (I'm running the Torque app via Bluetooth OBDII adapter to verify), then completely turn off (gauge needle drops to cold), then turn back on, but sit at a very low temperature. I've had a coolant temperature sensor related error code thrown (from memory it was "P0119 Engine Coolant Temperature Circuit Intermittent"), which confirms that the sensor is faulty.

So here's my thinking:

  1. I did the head retorque procedure because I figured the car probably hadn't ever had it done (the car is new to me), and that a loose head could introduce combustion gases into the coolant system, which would account for the expansion tank cap/valve from venting the additional pressure.
  2. If the coolant temperature sensor is dead, the coolant may well be at 110+ degrees, but the ECU thinks it's still cold and thus won't turn on the fans. In this case, the coolant would boil, and the associated increased pressure would force the expansion tank cap/valve open.
I ordered a new coolant temperature sensor (and thermostat for the future) last week, as I knew the sensor was faulty and would have to be replaced regardless. I'm REALLY hoping that I can fix this issue by simply replacing the faulty sensor. If that doesn't work, I can only assume I've got a head gasket issue, or even a cracked cylinder head. I also checked all coolant piping and fittings when doing the head retorque, and failed to find any leaks or splits. Given that the coolant level was constant for 3+ weeks, I don't think there are any leaks which would be dropping pressure and causing the coolant to boil prematurely.

Does my logic above make sense? If I replace the coolant temperature sensor and the gauge starts to work normally again, can I assume that this issue is fixed?
 

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My suspicion is you need a head gasket replacement. Get the vapors coming out of the expansion tank tested for exhaust gases to know for sure.

I have tried the head bolt re torque thing on two different cars with no positive effect what so ever.
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Discussion Starter #3
Thanks for your post. I'm really hoping it isn't a HG issue, but I really wouldn't be surprised if it is. I'll be changing the temperature sensor this evening regardless, and will probably take it to a Saab specialist here in Sydney for a cylinder leak down test to confirm a head issue.

Any other thoughts?
 

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If you are going to hire someone to do the head gasket (if indeed you need to) I'd recommend you set some time aside to get under the hood yourself when the head is out being machined and do some cleaning and perhaps swap out some stuff that might be close to needing replacement.

I did the oil pressure sender, the starter, the water pump, CPS, vacuum lines, swapped out the heater bypass (but I wish I did the McKay instead), belt tensioner (it was suspect at the time) basically anything that might be due because when the head is off there are 50 DIY's that are sitting there waiting for you to tend to with minimal grief.

The one thing I missed and it still bugs me to this day is not changing the AC expansion valve because when that thing failed I knew how simple a job it would have been sans head and throttle body etc etc etc
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Discussion Starter #5
Thanks again bob3000, much appreciated.

If it turns out the HG is in fact the culprit, I'll be doing the HG replacement myself. I would definitely look for any other suspect components while the head is off/being machined, so I appreciate your comments.
 

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Discussion Starter #6
Just a bit of an update. I wasn't able to swap out the coolant temperature sensor last night, as I didn't have a suitable sized spanner/shifter at my apartment, so I will have to wait until the weekend when I can get to the rest of my tools.

I ran the car with the expansion tank cap open, and filled new coolant to the required level. There were no bubbles whatsoever, which would suggest that the HG isn't leaking any exhaust into the coolant system. I monitored the temperature sensor on my phone (Torque app with Bluetooth OBDII adapter), and everything seemed to working perfectly.

I guess I'll see how the drive back home on the weekend goes, and then change the temp sensor and thermostat.
 

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Discussion Starter #8
From what you said, I'd suggest you change the expansion cap too. It might not be holding the appropriate pressure.
Excellent point! I hadn't even thought of that to be honest. I'll definitely have a look online and see if I can source one.

I've just thought of something else from last night which is quite strange. The OEM thermostat is either an 88 or 89 degree Celsius unit, which means the circulation of coolant to the radiator won't start until the coolant in the block reaches 88/89 degrees. I noticed last night that the thermostat clearly opened (i.e. the coolant level in the expansion tank dropped, prompting me to refill the expansion tank to replace the coolant that was left all over the road the day before), but the temperature reading at that point was around 78 degrees.

This reinforces my assumption that the cooling system itself is to blame for the issues I'm having. The thermostat is a mechanical device, which will open at 88/89 degrees regardless of the ECU or temp sensor. If the temp sensor is only reading 78 when it's actually 90+, there are going to be issues.

Further to this, with the car running at operational temp last night for around 10 minutes, sitting completely stationary, the fans never kicked in. Given that there was no flow of air through the radiator, I'd expect the fans to have kicked in at some point to maintain a reasonable temperature.
 

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You might want to have the head gasket checked anyway, when my head gasket failed the car would run fine under certain circumstances and then spew coolant and build gases at other times.

Its not always as simple as broken or not broken.

I did a compression test, showed as fine, I did the coolant contamination test it was inconclusive, lastly I did a cooling system pressure test and voila bad head gasket.
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Discussion Starter #10
You might want to have the head gasket checked anyway, when my head gasket failed the car would run fine under certain circumstances and then spew coolant and build gases at other times.

Its not always as simple as broken or not broken.

I did a compression test, showed as fine, I did the coolant contamination test it was inconclusive, lastly I did a cooling system pressure test and voila bad head gasket.
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Thanks for that bob3000, I still plan on getting the HG checked next week to confirm.
 

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I ran the car with the expansion tank cap open, and filled new coolant to the required level. There were no bubbles whatsoever, which would suggest that the HG isn't leaking any exhaust into the coolant system. I monitored the temperature sensor on my phone (Torque app with Bluetooth OBDII adapter), and everything seemed to working perfectly.

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you might have a HG leak that really only shows under load and high cylinder pressure. This was the case on my son's car. It would idle for hours and never boil over or pressurize the coolant system. If I drove it with high boost for 5 minutes the system was way over pressurized. The culprit was a small breach in the head gasket between the #2 cylinder and one of the water jackets.
 

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Thanks again bob3000, much appreciated.

If it turns out the HG is in fact the culprit, I'll be doing the HG replacement myself. I would definitely look for any other suspect components while the head is off/being machined, so I appreciate your comments.
There are a lot of things that are trivial with the head off that are difficult with it on.

The most obvious one is the timing chains and guides. A bit of a pain to do it with the engine in the car but it can be done and you've got a lot of the stuff off. When you take the tensioner out to take the head off measure it. If more than 15mm from shoulder to shoulder then I'd do the job.

Next are those things that are a pain to do with the engine in the car. Rear motor mount, coolant bypass valve and alternator come to mind. You might want to order a new set of brushes/regulator for the alternator since it'll be mostly out anyway. To this I would add a full set of studs for the exhaust manifold since they do get brittle and break and broken ones are a real pain to get out with the head in the car.

Next are those things you need to take off anyway (or nearly off). Serp belt, pulleys, belt tensioner. the water pump falls into this category even though you don't have to take it off but you've done 90% of the job.


The rest of the stuff I'd examine and if bad do it, but things like motor mounts, hoses, etc I'd only replace if I had to. Most of that stuff is reasonably easy to do with the head on.

Oh, a couple of more things since you said you're doing it yourself.

1: leave the exhaust manifold connected to the head, unbolt the intake and leave it in the car. The bolt on the end of the belts is a pain, get it through the space where the chain tensioner was. (you'll understand when you get it out)

2:unbolt the fuel rail and pull that and the injectors off and just flop the cables over onto the windshield, no need to disconnect

3: when yo u pull the head get help. (especially if you are not changing the timing chains) the chain guides are plastic and a twisting of the head will break one and then you are definitely doing the job. (yes, I did it)
 

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Your engine should maintain operating temperature as long as the thermostat works and no restrictions in the flow of coolant. If you feel the head gasket is fine, look at the flow of coolant. Radiator, water pump, thermostat and hoses. Have you replaced the thermostat and flushed the system? Your thermostat may just be sticky with age.
 

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Discussion Starter #16
you might have a HG leak that really only shows under load and high cylinder pressure. This was the case on my son's car. It would idle for hours and never boil over or pressurize the coolant system. If I drove it with high boost for 5 minutes the system was way over pressurized. The culprit was a small breach in the head gasket between the #2 cylinder and one of the water jackets.
The interesting thing is that I will drive the car quite hard, reaching 90+ load (measured via OBDII), and not have a problem. Then I'll be sitting in traffic, not having put any load through the engine whatsoever, and the steam will start coming out. If my symptoms were brought on with heavy driving, I'd totally expect a HG issue. Given that load doesn't seem to have any impact, and it only ever happens when I'm sitting in traffic, I'm leaning more towards a cooling issue.

There are a lot of things that are trivial with the head off that are difficult with it on.

The most obvious one is the timing chains and guides. A bit of a pain to do it with the engine in the car but it can be done and you've got a lot of the stuff off. When you take the tensioner out to take the head off measure it. If more than 15mm from shoulder to shoulder then I'd do the job.

Next are those things that are a pain to do with the engine in the car. Rear motor mount, coolant bypass valve and alternator come to mind. You might want to order a new set of brushes/regulator for the alternator since it'll be mostly out anyway. To this I would add a full set of studs for the exhaust manifold since they do get brittle and break and broken ones are a real pain to get out with the head in the car.

Next are those things you need to take off anyway (or nearly off). Serp belt, pulleys, belt tensioner. the water pump falls into this category even though you don't have to take it off but you've done 90% of the job.


The rest of the stuff I'd examine and if bad do it, but things like motor mounts, hoses, etc I'd only replace if I had to. Most of that stuff is reasonably easy to do with the head on.

Oh, a couple of more things since you said you're doing it yourself.

1: leave the exhaust manifold connected to the head, unbolt the intake and leave it in the car. The bolt on the end of the belts is a pain, get it through the space where the chain tensioner was. (you'll understand when you get it out)

2:unbolt the fuel rail and pull that and the injectors off and just flop the cables over onto the windshield, no need to disconnect

3: when yo u pull the head get help. (especially if you are not changing the timing chains) the chain guides are plastic and a twisting of the head will break one and then you are definitely doing the job. (yes, I did it)
Awesome mate, thanks for your help! If I end up needing to do a HG job, I'll be sure to follow your advice ;ol;

Your engine should maintain operating temperature as long as the thermostat works and no restrictions in the flow of coolant. If you feel the head gasket is fine, look at the flow of coolant. Radiator, water pump, thermostat and hoses. Have you replaced the thermostat and flushed the system? Your thermostat may just be sticky with age.
I haven't yet replaced the thermostat, I plan on doing that (with a new coolant temp sensor) on the weekend. The coolant has been more or less replaced, as every time the expansion tank has boiled I've lost 1+L of coolant. I did test my current thermostat in a pot of boiling water and it seemed to open, but it may well be sticky. Thanks!
 

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Discussion Starter #18
I just did the t-stat/sensor job and posted a write up here, if it helps you:

http://www.saabcentral.com/forums/showthread.php?t=551201
Thanks for that mate ;ol;

Just updating this thread. I got up early on Saturday morning, with hopes of driving the Saab from my apartment to my parent's place (where my workshop is) before the traffic became an issue. The Saab had other ideas however, as the battery was completely flat :eek: I must have dislodged something near the terminal when I fiddled with it a couple of days prior, causing some current leakage.

Attempt #2 on Sunday morning. I jumped the car and drove to my parent's without issue. The temperature gauge was working, but the temperature from the sensor itself (read via OBDII) was going between 80 degrees and 100 degrees fairly consistently, without any real change in driving conditions/load.

Once in the workshop, I popped off the upper coolant hose (and let the coolant drain out), then removed the thermostat housing and thermostat. I installed the new thermostat, replaced the thermostat housing and then turned my attention to the sensor. A 19mm box spanner made fairly light work of the temperature sensor, but I'd highly recommend removing the battery to give yourself some decent access.

The old temperature sensor was showing considerable signs of deterioration, with discolouring and even some slight rust forming on the probe. I installed the new sensor, clipped in the wiring harness, installed the upper coolant pipe and battery. I started the car and let it warm up, once again monitoring the temperature via OBDII. The car reached ~90 degrees before the thermostat started to open (as expected), as evidenced by the coolant level in the expansion tank dropping. I topped up the expansion tank (to replace the coolant lost when changing the thermostat), and let the car idle for 10 minutes at operating temperature.

I ended up loading up the Saab with a custom dining table I made on the weekend (wood table top in the wagon with the rear seats down, metal framework on the roof racks :cheesy:), and drove back to my apartment. There was a very noticeable difference with the new sensor and thermostat in place:
  1. The temperature seemed more consistent. The rate at which OBDII showed the temperature changing up/down was noticeably less than before
  2. The car's operating temperature was higher. I would see anywhere from 75 to 85 degrees for normal driving conditions previously, whereas it will now sit comfortably between 85 (no traffic) and 100 (stop and go traffic)
  3. The fuel economy is much, much better. I was seeing figures in the 13+L/100km range beforehand, and am now seeing figures in the low to mid 10L/100km range.
I've only put around 20km on the car since doing the replacements, but I already have more confidence in it. I plan on taking the car out for some more aggressive driving this evening, to see how the temperatures hold up under heavy load. I'm hopeful that if it passes this test with flying colours, the issues I've been having with the boiling expansion tank may in fact be resolved :cool:
 

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Discussion Starter #19
I figured I'd wrap this thread up, in case anyone has similar issues in the future. This issue was 100% fixed by replacing the coolant temperature sensor and thermostat. My coolant system has operated perfectly since doing the replacement, with the coolant level remaining unchanged whatsoever.
 

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Suspect the pressure cap

Years ago on my old 900 turbo 1979 version........I had the engine rebuilt and it would boil over after 15 miles of driving. Stumped me and my chechanic for weeks.

I changed the pressure cap and it fixed it. System maintains 12-16 psi range. If the cap vents at 7 psi it will puke half or more of your coolant.

This is a $5 to $7 part!!
 
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