'90 V8 Quattro Water and Oil Temperature Help

My water and oil temperature gauges are both reading 60-65C. From what I've gathered, the water temperature should be higher, around 90C. I assume the
water and oil gauges should read similar temperatures and since they do, I assume they are correct.
Is checking the thermostat the reasonable thing to do? Is this a relatively easy thing for a novice mechanic? Where is the thermostat on this engine?
Thanks, Tom
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wrote:

Wayter temp should be near 90C when the engine is hot. My '90 Audi-90 had chronically low water temp reading and very slow warmup after about the 4th year during the winter. I suspect that the thermostat was stuck open. It's a bitch to change on the -90. You have to remove a bunch of stuff to get the housing off.
Oil tempertature should be a bit higher. Between 200-250 F (95-120C) is about right when the engine is fully warmed up. You always want the oil to be close to or above the boiling temperature of water, so that any condensation in the crankcase is eliminated when the engine is running.

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So other than a faulty temperature gauge, what could account for a low oil temperature?
Thanks, Tom

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