1) Maybe we should assume Susan knows little but is willing to learn? We've been writing as if the poster knows where all these components are and how to check them. With all due respect to all involved.

2) Any temp gauge oddities - she should get the compensator board bypassed before doing anything else. There's nothing quite like having a gauge that lies like a rug when you're figuring out temperature issues. That's a job that a newbie can do with a screwdriver or two and a pair of pliers (for the retaining nuts behind the headlight switch panel). But we should see if she's listening here.

2) Likely lack of a t'stat or a very-low-temp t'stat. This needs to be checked. Needs a willingness to get dirty or have a helpful friend or shop.

3) Failed fuel pressure regulator can also cause over-rich mixture. If Susan is still listening we can help her find it and sniff the correct thin hose.

4) And, as posted by others, a good run through the basics is in order (tune up, air filter, reasonable weight oil etc.).
HOWEVER poster may have already done a lot of this stuff recently so we need to hear from her.

5) Definitely do a real mpg check. Fill tank till hose clicks off 2nd time. Zero the odometer. Drive 200+ miles. Refill - again to the 2nd click-off - and then do the math from the qty of fuel needed at that fillup. Anything else is not informative even to the owner/driver.
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DAMHIK: Don't Ask Me How I Know - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 500 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).