Insight : Tom Townsend a.k.a. "SAABTECH"
Engine coolant should be maintained to promote both its effectiveness and the longevity of the engine and the entire cooling system. Over time, and with those occasional top offs, the coolant becomes unknown and begins to break down. Phosphates and silicates and produced aluminum oxides fall out of suspension building up and promoting electrolysis, pitting of the aluminum surfaces and the main gaskets and seals. The deposits of these phosphates and oxides in the layers of the head gasket splits it like ice in pavement. Concentration becomes unknown and thus its freezing point unknown. Mixing common ethylene glycol and the newer, supposedly environmental friendly, propylene glycol, produces a mix with a specific gravity unreadable by ball drop type testers meant for either one or the other of the coolants. Use one or the other, but do not mix. Because of this, you might want to keep a little of what you're using around, just in case.
We have found increased life and fewer failures of any kind in the cooling systems after using Mercedes Benz factory coolant. It is phosphate free and pH buffered with inhibitors to aid in the prevention of electrolysis. When servicing cars that have been using it, the difference in the appearance of the internal cooling system is noticeable. Upon thermostat replacement, the aluminum is not covered with the white aluminum oxide or pitted from electrolysis as is common with the green coolants routinely used by some.
The coolant of your choice, unless it specifically states otherwise on the container, should be kept at the least concentration necessary to insure proper cold weather protection for its expected needs. As close to a 50% coolant to water mix as you can get is best, as long as the coolant's label's freezing point chart is followed to insure adequate protection. Running pure coolant is not a very good idea, more is not better. Particulates are more apt to form at higher concentrations.
We service the cooling system on our customers cars every 30K miles with a drain, a flush, a thermostat replacement, a tightening of all the cooling hose clamps, pressure test for leaks, inspection of all hoses and replacement of any upper hoses (top radiator and bypass hose at rear of head) that are over three years old, fan operation, coolant refill and relay upgrades.
(Look here for more info and pictures)
Thermostats are considered a maintenance item in our book. They operate by use of a fixed volume of wax that expands a calculated amount at certain temperatures, pushing them open. Each cooling system cycle works the thermostat, exposing it first to temperatures above what it is set to open at, then, after it gets hot and opens, it is flooded shortly with much cooler water, so it closes. It oscillates between open and closed as the engine is driven to maintain an even cooling system temp. The thermostat works more than its commonly perceived opening once per trip. This wears them. You can see evidence on the brass bodies of thermostat where they begin to cock and bind in their travel. Let them catch here just once, and it could take out the engine. While you are examining the thermostat, look at the top of it, where the chamber holding the wax is sealed. Most older thermostats, failed and not yet failed, show evidence of leakage of the wax here. Since that wax is calculated in its volume and expansion rate, any leakage changes its properties and amount of opening. Overheating by running low of coolant can subject the thermostat to much higher than normal temps which could rupture its seal and allow the wax out, or overheat the wax to the point it changes in its character. Anytime the car overheats, I would consider replacing the thermostat, the trust is gone. The thermostat in a 900 sits under the housing that the upper radiator hose attaches to on the engine. 8 V's have easy access via two 13 mm bolts. 16 Vs' require the removal of the AIC valve to service the thermostat. Unplug the valve, remove its two hoses, and then remove the 10 mm bolt holding it in its bracket. Set it out of the way (now would be an excellent time to clean its shutter wheel with carb cleaner). Now you can remove the two 12 mm bolts holding the housing and access the thermostat. On a 9000, the thermostat sets on the rear of the head on the driver's side, still under a housing to which the upper radiator hose connects, more of a task to access than the 900s though. There are various things attached to this housing, from fuel pressure regulators with their 4 mm Allen's to DI ground wires and brackets on later 2.3 engines with 4 mm Allen's or 10 mm bolts. Often it is time and knuckle saving to remove at least the rubber bellows going to the throttle housing. 2.3's require removal of some throttle housing hoses to get to the thermostat so that it can be accessed and cleaned properly on the mounting surfaces.
On cars with a rubber seal for the thermostat gasket (all except the early 8 Vs), clean the housing surfaces with a brush. No sealant should be necessary for the gasket. Make sure that the bolts are clean, wire brush their threads and use an anti seize compound on them to prevent future troubles. Install the thermostat so that the brass air bleeder valve on it is at the highest point. Turn the lower plate so its hole is in alignment with the brass fitting hole. On 16 V thermostats, turn and position the hole in the bottom plate to align with the bleeder on the top of the thermostat. This allows all the air to leave the system. Though the 9000 has no bleeder port to the exterior, its thermostat design allows it to empty air to the reservoir, if the thermostat is properly aligned.
Use a factory thermostat. In all but the coldest climates, we recommend the 82 degree Celsius thermostat under the part number 8817538 for 16 V engines. The 8 V has its own thermostat, number 9337551. Do not install a 8 V thermostat in a 16 valve engine. The 16 V has a special design and it is for this reason also that we don't recommend aftermarket thermostats.
Too much depends on such a relatively inexpensive part. The three position design of the Saab thermostat allows proper operation of the cooling system. Some attempts at copying it have resulted in overheating or loss of cabin heat when the car gets warm. Either requires doing the thermostat again, so why not go ahead and put what was designed for the car there, not just one that fits the hole.
Check the operation of the cooling fans. On 900s, the sensor is in the upper left hand corner of the radiator with two wires connecting to it. Disconnect the two wires and touch them together. With the key on, both fans should run. 91 and up 900 S's should be checked for the modification and replacement of the cooling fan relays if only one fan runs.
Look for the bulletin 03/92-0191 entitled High Temperature Gauge Readings. It will tell you to remove the stock Bosch relay in fuse box position J. Throw this relay away. Then you remove the two screws holding the fuse panel down and lift it up. Find wire # 111B, a green wire coming from relay position H pin 87. Leave this wire attached to its relay, but splice into it with a new wire you supply, (don't cut the old wire, just skin its insulation back, solder in a length of your new wire and insulate the solder joint) add a terminal (part number 79 71 708) to the end of your splice wire and insert the new wire terminal into position 85a of position J for the new relay. The replacement relay for position J is part number 85 72 190. After you install the new wire and terminal and are certain that it is secure, reinstall the fuse panel and its screws. Then plug the new relay in position J. Now, check your work by turning the key on and removing the two wires on the fan sensor on the left of the radiator. Jumping the two wires together should cause both cooling fans to run. If only one fan runs, check that it is getting power and ground before replacing it. On 86-88 9000s, the switch is the same, only located in the lower right side of the radiator. Jumping its lead should turn on the fan. On newer 9000s, the cooling fans can get complicated, starting with their two speed functions and their three wire fan sensors. WE HAVE A COOLER FAN SENSOR FOR THESE CARS (LOOK HERE FOR WIRING INFO) You can check the fans by removing and jumping across the fan relays pins 1 and 2 ( +30 and 87). This is the low speed for the fan a should be engaged first to limit fan draw. The relay lives in the fuse/relay box in the engine compartment on the left side. The relay is in position E for the test. If a time delay relay is here, I would rewire to use a standard relay. Saab had a bulletin for this, 02/93-0305 entitled Radiator Time Delay Relay. On 89-> 900s the fix is a direct swap, exchanging the factory relay part number 9663339 in relay/fuse box position G with the new 8522310 relay. The exchange is the same for a 9000, but requires rewiring. It is located in the engine compartment relay/fuse block position E. Check the pin 86 position for a connector. If one is present, just plug in the new relay. If it is not, you must jump a wire from pin 30 and add its connector to pin 86 before swapping the relay. Since Saab is eliminating the time delay function ( limits the time the fans run after the engine is shut off) on these cars, we recommend eliminating on earlier models as well. Starting with the 84 cars, the time delay relay was installed on the left fender well, not in the fuse box. It will have 4 wires going to it, two (yellow/white) of a larger gauge than the other two. To eliminate it, simply remove the relay, clip the larger two wires and solder/insulate them together. Leave the relay disconnected. This bypasses the relay. When these time delay relays fail, and they all eventually fail, they do so in one of two ways, they either stick closed and run the battery down or they stick open and prevent the fans from coming on. They cost at least $85 for replacement and eliminating them prevents future troubles. On the 89-> cars, the modified relay is both less expensive and more reliable than the relay that is there.
To check the high speed operation on equipped 9000s, first engage low speed as above and then remove the relay in position F of the same fuse box and jump the 1 pin (+30) to both the 2 (87) and 3 (87B) terminals. This should generate warp drive captain. If the fuses for the cooling fan haven't been updated, change them to 30A in the fuse box under the hood, as per factory bulletin 03/89-1127 Running Change Upgraded Fuse For The Cooling Fan.
For all 900s and Early 9000s with the two wire fan sensor, we strongly suggest you swap the original fan sensor that turns the fans on the first time at 92 degrees Celsius for one that turns them on at 82 degrees. When used with a factory 82 degree thermostat(8817538), this avoids the temperature overshoot problem seen when getting in traffic after highway driving, and maintains the gauge reading at about halfway. The sensor simply screws into and out of the radiator and the wires plug right up. We use a sensor made by Wahler for VW. You can get this sensor from a VW dealer under the part number 823959481D, or from us if you can't find it. That is a pretty old VW part number now, but it is what we order it under. We have not found a cooler direct replacement for later 9000s with the two stage fan, but are searching. You can rewire them to accept the cooler old style switch, but that is detailed in another page on this site.
FLUSHING, FILLING, BLEEDING
To flush the cooling system, find a suitable pan to catch the old coolant. Drain it first from the radiator drain. Be careful if the petcock seems tight not to damage the radiator. On 900s, the drain is on the right lower front of the radiator. Early ones have a 17 mm petcock with a 22 mm support hex. Later ones have a 24 mm plastic petcock. 9000s' have a petcock accessible from the bottom on the right side. They are hard to get to without removing the under panels and can become brittle and break. You might find it easier to remove the bottom hose on the water pump, below the AC compressor.
Make sure on cars with manual heat controls, that the temperature selection on the heater is set to hot. This opens the hot water valve and allows the flushing of the heater circuit and core. On 9000s, the heater circuit is open all the time, there is no need to set the temperature. After the most of the old coolant has drained, open the heater circuit by removing a heater hose and inserting a garden hose. Then you can proceed to flush the system by running water through the system until it comes out clear. This can take up to an hour. On a 900 with an 8 V engine, we remove the coolant hose running to the center of the intake and flushing through it into the heater. On 16 V 900s, remove the hose coming up from behind the AC compressor off a pipe running to the front of the head, flush through the end of that hose. On the 9000s' removing the smaller hose connecting to the rear of the head (facing the left side of the car) allows its heater core to be flushed through that hose. We flush the systems with the thermostat removed and replace it when finished. Swapping the point at which you place the garden hose, from the initial heater hose for the majority of the heavy work, to the reservoir to rinse it and its hoses, to the top radiator hose, anywhere you can stick it in the open system, will make sure no old coolant gets left lying around. When it all looks nice and clear, let the engine drain. Then shut up anything you have opened, getting the system ready for its new coolant.
Pour in the required amount of coolant, making sure to leave the manual heat controls on hot. On a 900, there is an air bleeder port on the thermostat housing. It has two 11 mm (7/16") hexes. Hold the lower one and loosen the top one to allow trapped air to escape the system. Fill with the coolant/water mixture until the reservoir is to the max line on 9000s and until a steady stream of coolant comes out of the air bleeder port on a 900. Then shut the bleeder port on a 900 and fill to the max line of the reservoir. Check for leaks. Then start the car and let it idle. Pay attention to the reservoir. If air comes up (it will), re adjust the level. Run the car until the fans cycle once. You might want to reopen the bleeder screw on a 900 after the car runs a few minutes just to make sure there is no trapped air. After the fans cycle, recheck and adjust the level at MAX if necessary. Replace the radiator cap and run the car until the fans cycle again and shut it off. Let it sit for 15-20 minutes and check for leaks after the system builds all the pressure it should. After a complete cool down, recheck the level. Do this again just to be sure after another temperature cycle.