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Engine WarmUp MPG
02-12-2013, 09:23 PM
Post: #1
Engine WarmUp MPG
1990 Cadillac Deville 4.5 L FWD

Is It Normal To Wait 15 minutes of driving before my MPG becomes stable
and good normal levels in the cooler climate ?
Could this be a symptom that the Engine ( Computer ) is in Closed-Loop
until Engine / Coolant / Thermostat Temperature reaches a good operating point ?
Should I suspect a possible problem ?
Possibly in the A.I.R. Air Injection Reactor System section or other ?
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02-15-2013, 12:42 AM
Post: #2
RE: Engine WarmUp MPG
I'm not sure how to answer this. I would say that if it has always been that way & the Check Engine light isn't coming on, it is likely normal.

Rupe is on vacation. May-be he will have better insight to this when he returns?

Sorry I can't be of more help.

Thanks for using the forum,

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02-18-2013, 03:01 AM
Post: #3
RE: Engine WarmUp MPG
It may be as simple as needing a new thermostat. You should be able to reach "normal" coolant temp with only around 5 miles of driving if it's above 20 F outside. At idle it may take 10 - 15 minutes just running the engine out in the driveway at similar temps.

As for "MPG" you must be talking about the dash computer display. Some of that info is available on a good scanner if you really want to compare notes.

I guess what we really need is clarification on the question. Is this about the engine taking too long to get warm or the display not reading correctly or maybe you actually have poor mileage? We'd also like to know what your idea of "cooler climate" is. My MPG stinks on the highway when it's 15 degrees out and it goes up quite a bit for the same trip when it's 75 degrees out.
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