Re: my gauges arn't faulty
I agree (partly) with GreenMachine -- OTH, if you're going to take off the 'stat cover you'd be best off putting in a brand new one and don't bother buggering with drilling holes. Engines are meant to have 'stats built to specific standards, that way they run best.
BTW, it's winter now and your limo is 8 years old... Why not take it to the radiator place and have them work over the cooling system in time for the heat? They can also suss it for any faults you haven't seen yet -- BEFORE they become embarrassing! You may also want to follow Ford and Toyota by throwing out the glycol-based anti-freeze/boil and put the new non-toxic engine-friendly additive in. Ethylene glycol MUST be replaced every 6 or 12 months depending on the brand -- if you don't, it degrades to corrosive by-products which is why they put anti-corrosion in it... If you have even a pinhole in your heater the stuff can intoxicate you, literally. If you email me I can give you details of an environmentally friendly coolant additive made here in WA -- not by me, and I don't sell it either.
Your oil sounds like you may want to do a flush. It could be you're getting small dirt through the bypass into lifters & etc. Buy 5 liters of el cheapo oil, and an el cheapo filter, and a bottle of flushing goop. FOLLOW THE INSTRUCTIONS ON THE GOOP TO THE LETTER. Run the el cheapo oil for about 100-200K's, then drop & fill with your fave brand, with a really good filter.