Long idle times & Interstate driving

Not open for further replies.


Aug 26, 2005
My wifes 1999 Expedition see's very long idle times. Sometimes up to a 1/2 hour or more. (First Responder) But here is my question.
The Expedtion also see's long runs down the interstate for 2 to 3 hours.
Is that enough to get rid of the fuel in the oil?
Or should I be changing oil more than than every 3000 miles as I have done since new. It has over 100,000 and does not burn,leak or use oil.
I have always used Tropartic 5w30 synblend and a Motorcraft filter FL820
Is there a formula on idle time in proportion to normal mileage on an OCI? Would one add 30 miles onto OCI interval for every 1/2 hour idling? Sorry I cant answer your question but this might be onto something from others in BITOG.

I believe the fuel would burn out in highway miles, I also believe a good computerized clean fuel injection system does not overfuel as the old carburated systems years ago.

I do 3K OCI on everything I own no matter what the conditions. Blue 99 is right keeping your Expedition at 3K OCI, I would not increase OCI LC. If I were hypothetically doing hypothetically longer OCI's on normal conditions and then started doing excessive idling I would deduct miles off the 5K OCI in some formula for the long term idling minutes. Moot point for me dedicting miles, 3K miles is my standard OCI for me because all my miles are generally extreme in climate, conditions etc.


I think that you are changing oil too often at 3K miles.

Do an UOA and see what the actual condition of the oil is at 3K miles to verify extending the change interval.

I have the same driving conditions and have extended from my pre-BITOG 3K miles to 4500 or 5000 miles. No impact to anything except some $$ savings.

Car is a 95 crown vic p71, 122K miles, MC oil filter and MC 5W-30, Havoline 5W-30, or Pennzoil LL 5W-30. Runs like new, engine is very clean inside as well.
I agree on the UOA if you want a higher level of assurance. It's really the only way to know for sure without spending a ton of time or money and elminates a lot of guess work.

With 2 - 3 hour interstate runs a well tuned engine should not have problems with excessive fuel or soot dilution.
Ford recommends 200 hours OCI for this type of service (extended idling), but does not supply the engine hour meter. Source: factory service manual.
I would guesstimate that 5 minutes after the crankcase oil has reached 100C(210F), full operating temperature, all the fuel & condensation components in the oil, capable of being removed by elevated temperatures, will have flashed off.

At highway speeds, the crankcase oil is fully circulating at about 5-6 times a minute. The primary heat source is the 300F+ piston bottoms and this exposure is what drives the fuel & moisture contaminates out of the oil.

Idling for up to 1/2 hour at a time will increase the load of combustion byproducts & soot that the oil has to carry, but a 3000 mile OCI with today's GF-4/SM formulations is still very conservative, no need to shorten this up.
This is where a "fuel consumption" factor would be useful.

Try this, just track the fuel consumption for her next OCI. Do a UOA. Adjust as allowable in "fuel factor".

No, I don't expect you to do this ..but it would make for some interesting posts.
I wonder if as a First Responder she drives hard on a cold engine, and what could be done about it.

Remote start is high on that list; start the truck up when she gets the call/page and the oil's flowing by the time she actually takes off.
I would say in most cases the truck is not driven hard on a cold engine. It is in a garage and most of the time the block heater is plugged in.(I know the oil is still cold)
As for keeping track of fuel consumption!

At 5 to 10 mpg in the winter months.
It would be easier to track snow flakes!

Thanks for your replys
I'm not into uoa's myself, but I think it might be a good thing in your case. Long periods of idling with modern FI systems should'nt be a problem. In the old days with carb engines, it could be a real issue.

You have to understand what gas is. It is a solvent as well as a drying agent. Fuel in the oil will create varnish. The most important issue is to keep the PCV system in perfect condition. You relly need to be anal about it.
Other than changing your PCV valve what else can you do to keep your PCV system in perfect condition?

Also, how often should you change your PCV valve? I just did mine recently.
Not open for further replies.