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Discussion Starter · #1 ·
I just finished replacing the Head on my '96 900S. It restarted but the oil pressure light is on and doesn't go out, did I knock off the sensor wire somewhere? Also I now have a leak where the fuel injector rail connects to the #4 injector. How do these go together/come apart? I assume t is a press fit but do not want to "force" it if this is not the case I have removed the little clips between the injector and rail. As always thank you for the suggestions this is my first Saab that I have been this deep into and your help is greatly appreciated.
 

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Discussion Starter · #2 ·
Further Along

OK, things are progressing. I have the car running oil pressure was indeed a loose wire. I still have no indication from the water temp. guage it comes up when the power is turned on but does not rise as the engine temp increases. I have purged the water system and think it is working correctly. The radiator fan does not come on even though I believe the temp. is up to the point where it should come on. Does anyone out there know what's next? Do I possibly, coincidently, have a faulty temp. sensor now?;oops:
 

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Discussion Starter · #4 ·
I ran it some more this morning while keeping an eye on things. First I checked the fan to see if it would run by connecting directly to battery it will run on one of the levels but not the other. I am begining to think that the reason that it needed a head gasket is because of overheating! Watching the guage it did start to climb but was definatly behind the actual temperature. When the guage reached about 1/2 way up he normal range the car overheated. Thermostat is new with the headgasket/head change.
 

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It's best to test the fan from the relay sockets in the relay and fuse box under the hood and near the firewall. (That way you are testing the connectors and wiring to the fan along with the fan.) You can check the fan fuses at the same time. There are separate fuses and relays for the low and high fan speed.

If the fuses check ok and if the low fan speed does not work, a resistor which is in series with the low speed circuit may be burned out. That's common, it is a wire-wound resistor inside a cheap metal tube filled with ceramic powder.

As the temp goes up, the fan is supposed to turn on at low speed first, then high speed. The gauge being behind, or "slow" is just a function of the software that controls the gauge and other things on the front panel. The ECU samples the temperature instantaneously.

If the engine overheats, and you shut the engine off, and leave the ignition and gauges on, I think you can observe the needle go up past the middle. It usually goes up to the middle, then it pauses for a bit, then it goes up a bit more, before finally starting to go down, because the engine stays at over temp for some time.
 

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Discussion Starter · #6 ·
OK, I have checked the fan from the relay position and it appears that the fan will run on both high and low from here. I am assuming from this that the computer never sends a signal for the fan to turn on. I am still thinking it is the water temp. sensor. Is the fan signal and the guage reading come from the same sensor? Also are there just the 2 sensors in the system for temperature? Thank you for your help.
 

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Discussion Starter · #7 ·
Another note: I tried turning on the A/C and the fan doesn't come on then either? I did swap relays around with ones that I know are good and there was no change.
 

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If the head gasket blew there should have been coolant in your oil and oil in your coolant. You would have probably noticed and changed the oil but maybe you forgot to flush the coolant.

Having oil in your coolant can cause overheats too. It may not have been what caused the initial overheating of your engine but it is a probable cause for the present overheat situation, especially if your thermostat is new and the fan works properly as well.

I would drain the coolant from the radiator, blast water through the system for a good long while, then refill the coolant.

Hope that works for you.
 

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I just read the thread again and you said that you already purged the water system... hmm

i guess it would not hurt to flush it again but I agree with Ron on this one and double check the thermostat to see if it is working like it should. If it does work you should feel the coolant moving through the hose that connects to the thermostat housing once and a while.
 

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... Is the fan signal and the guage reading come from the same sensor? Also are there just the 2 sensors in the system for temperature? Thank you for your help.
There are two engine temp sensors. The coolant temp sensor which is used for the gauge, is on the side of the engine. At least on the turbo model, there is another temperature signal from a sensor on the intake manifold, which is used for engine control. Bottom of pic below. I am not sure which sensor controls the fans, but if you have a copy of the Saab WIS on CD, I believe it tells you which one.



The radiator fan also cools the AC condenser, and is supposed to run on LOW when the AC compressor is on, regardless of the engine temps. That is according to the Saab documentation, and it does work that way on my car. I can't be 100% sure your model works the same, but I would think so. If the LOW speed circuit never comes on, the AC may overheat in traffic, when the car is not moving (mine did).

Fan Temp Settings:

* Thermostat opening temp: 89 +/- 2C
* Fan Low speed turn on: 100 +/- 2C
* Fan High speed turn on: 113 +/- 2C
* AC disabled at: 126 +/- 2C
* Temp gauge at mid point (9 o'clock) 85-115C

Other Fan Info

Stupid Q., maybe, but since you had the intake manifold off for the work you did, is it possible you did not connect that sensor, or perhaps missed some ground connection? See post linked below...

http://www.saabcentral.com/forums/showthread.php?p=1751422#post1751422

Btw, you should not rely on the oil light after doing any major engine work, because it comes on only at VERY low oil pressure, so just because the fault light is off, does not mean the oil pressure is good.
 

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Discussion Starter · #11 ·
PMI, thanks for all the great information I will get back to it tomorrow evening after work. The car has an "add on" oil pressure sensor and guage so I was relying on that for actual pressure reading but was annoyed and worried by the big red triangle and oil can lights, even though guage showed pressure. I will recheck connections and try the jumpers in the relay sockets as well. Thanks again for all your help, wife is starting to think I should just keep playing with my pickups Diesel.
 

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Discussion Starter · #12 ·
I just had a few minutes to do some checks. I did the jumpers in the relay sockets- The fan works on both High and Low from there. I double checked the sensor connections and they appear to be connected. I just ordered both sensors and will install them tomorrow night.
 

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Discussion Starter · #13 ·
Glassybarrel, I did flush the system before refilling. The headgasket failure was between a water journal and the compression chamber causing the coolant system o become over pressurzed. There was no indication of cross contamination between water and oil but both were flushed and changed. I kept track of the top radiator hose as the car warmed up. It stays relativly cool for a little while and then you can feel it get obviously warmer as the thermostat opens, it is also apparent there is a flow through the hose. Thank you for your suggestions all are greatly appreciated. I am double no triple checking all grounds and connections when the sensors come tomorrow.
 

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I double checked the sensor connections and they appear to be connected. I just ordered both sensors and will install them tomorrow night.
Given the other work you have already done, a couple new temp sensors is probably a good investment. However, the one on the back of the engine can be a pain to get out, and you can do a simple test with a cold engine on the old ones if you like. The sensor elements inside the sensor are the same type, and they will have the same resistance if the two sensors are at the same temperature. So, once the engine has cooled off, you can test the sensors against each other (or any similar sensor in the car). Just unplug the connector, and measure across the two pins.

Btw, could you post your oil pressure readings? I don't think we have much oil pressure data on your model.
 

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Discussion Starter · #15 ·
OK, first I want to thank you all for your input into this problem you have been very helpful. I replaced the 2 temperature sensors and everything works as it should. Guage and fan seemed to be controled by sensor on back of head but replace one in intake manifold just because. I bought the car with a known headgasket problem I guess now I know why it had the headgasket problem.

Ok for general information the car has 229,000 mile so for what it's worth the oil pressure readings when I got it running again were approx. 25psi at idle and it runs at about 50psi at cruise, I am not sure how these compare with any others.:D
 

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25psi at idle and it runs at about 50psi at cruise, I am not sure how these compare with any others.:D
Thanks, that sounds about right. I don't have enough information to say much about the oil pressure at idle, but basically it goes up with rpm, until the oil pressure reducing valve takes over.

At 2000 rpm, it is supposed to be 2.7 bar, or about 40 psi. I believe that is what most mechanics test for.

The oil pressure reducing valve is supposed to open at 3.8 bar (55 psi). I don't think that is very accurate though, and not that much real data from older cars has been posted.
 
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