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Re: Buying a Used SPG
Posted by Dave Ream (more from Dave Ream) on Mon, 17 Apr 2000 10:37:51
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

Sounds very reasonable to me if he's taken care of it with regular
maintenance and proper operating procedures. Peruse the maintenance
records. Ask him to take you for a drive, and observe how he treats the
car. Does he treat his turbo like you treat your turbo? (idle for 15
seconds or so at start up before engaging, idle for 20 seconds or so before
shutdown?) Ask him it if you need to feed it premium fuel... (I believe the
owner's manual says Yes, his answer will give you an indication of how he
treats the car).

The only real differences between your car and his car, if I remember
correctly, are:
1. rocker panels/body styling
2. different suspension springs (stiffer, & lowers car about 2 cm) & shocks
3. different turbocharger (different flow map, winds up a bit faster)
4. you can tow up to about 2,000 pounds, SPG can tow little if anything, and
5. SPG requires higher octane fuel.

Except for the turbocharger and possibly the engine control data (see
below), I believe the engines and engine mounting configurations are
identical. Should be a straight bolt-out, bolt-in swap.

One thing to check on if you consider swapping engines is whether the SPG
has different engine control data for the computer (computer
data/programming). I would not be surprised if it did, especially
considering the horsepower difference. If so, swap that along with the
engine!

Of general interest, you might also check in your owner's manual, it
probably contains sections for both the 900T and the SPG that you can
compare. (The '88 owner's manual does.)

Sidenote, for the '88 models, 900T had 160hp, SPG 165hp; for your year
(1990), 900T had 160hp, SPG 175hp.

As to what might go first, my bet is the transmission, if it has not already.

Weak spot is the transmission, I had mine rebuilt at about 115K ('88 900T,
currently at 198K and apparently strong), my brother had his rebuilt at
about 175K ('86 900S). Transmission rebuild is pricey, in the neighborhood
of
$1,700 or so, mostly labor; engine must come out. Good time though to
change a leaky rear main crank seal (which incidentally will prolong the
life of your alternator if that seal is leaking, theory is that airflow in
the engine bay will carry enough oil mist/vapor whatever up to the
alternator for it to breath and thus grab dust/dirt and make life harder on
moving parts such as bearings) & other little stuff that's easy to get at
with the engine out. On mine they also changed the main crankshaft pulley
(that drives the waterpump, alternator, A/C, etc.) because it was starting
to separate.

There is stuff in the archives about using specially formulated oils in the
manual transmission instead of 10W30 motor oil, I think it is a *good
idea*. Red Line has a good website, and they explain why an oil specially
prepared for a manual gearbox is a good idea and why motor oil is a bad
idea. Two main points they make are, a) if the oil is too slippery the
synchros won't function properly, and b) motor oil does not provide extreme
pressure lubrication. 10W30 motor oil has the right viscosity/friction
properties to keep the synchros happy, but it does not protect the
gears/bearing surfaces in the gearbox very well. This is because some motor
oil is burned during normal engine operation, and thus a motor oil must
both lubricate and not be harmful when burned. Additives that provide
excellent extreme pressure lubrication/protection are not put into motor
oil because the ash they leave in the combustion chamber is not good. But
gear oil does not have to burn nicely! So, bottom line, if you are not
already doing so, use a good manual gearbox oil like Red Line's synthetic.

In the records you should find evidence that the water pump was changed out
at about 100K or so, if not then good idea to either change it out and stop
worrying or watch it like a hawk for signs of leakage.

The turbocharger can be expensive to replace. I just replaced mine at 198K,
to the tune of $1,400. The oil feed tube to the turbocharger bearing was
nearly occluded, the bearing had excessive play. Symptom was intermittent
smoke (burning oil) from the exhaust with warm engine, idling at stop
lights. Lots of smoke under hard acceleration/boost can also be a sign of
an ailing turbo.

I bought the car with 90K on it, and I've been reasonably good about idling
out (startup, shutdown) & regular oil changes... I don't know for sure what
caused the series of events that resulted in turbo bearing failure. I do
have a theory, though. On one oil change not long ago, I changed the oil
and filter with the car on a slope and did not drain as much as I normally
do, and then put in 5 qts (which I normally do). Now, 5 qts will usually
put me up about 1/3' on the dipstick above the full mark. This time, it was
about 2/3' above the full mark. How could that make a difference? Well,
there is a largish metal tube (about as big around as your thumb)
connecting the bottom of the turbine housing with the crankcase. This is
the oil return tube from the turbo bearing. The oil is provided under
pressure to the top of the turbine bearing, and then it flows down out of
the bearing into the oil return tube. The turbine spins fast, up to about
70,000 rpm or so, and the oil that comes out looks like dirty cream and is
a little frothy, a little aerated. This is one reason why the return tube
is so large, so that the foamy oil will drain properly. However, if the oil
return tube feeds into the crankcase *below* the oil level in the crank
case, then the frothy oil won't drain because it is less dense than the
liquid oil in the crankcase. If it does not drain, oil flow through the
turbo bearing slows/stops, which increases the thermal load/temperature of
the oil that remains in the bearing, causing the oil to 'coke' and
solidify, which chokes the oil passageways into/through the bearing, making
things worse and so forth. I don't know Saab's safety margin (at what point
on the oil dipstick the oil return tube outlet into the crankcase is
immersed), so I can't be sure. And, it could have been a combination of
this with other factors relating to age (oil-born crud buildup, not enough
idle-down once or twice, ...) But, food for thought. If you are interested
in turbos, try Hugh Innes's (? MacInnes?) book (entitled 'Turbocharging' or
something like that), published by HP books (do a search on Amazon.com on
turbo/turbocharge/turbocharging, etc., it should come up). It is a
well-written classic that has been in print for many years.

I replaced the clutch when I got the car at 90K, I think that ran about
$600 back in 1992, seems to be doing fine.

Well, I may have written more than you wanted to read.
I hope some of it is useful, good luck.

Regards,
Dave
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