1999 C280 using oil

My 1999 C280 has started consuming oil. It has just over 118,000 miles and up until this point never used any oil between changes. It now uses about 1
quart every 500-600 mile when on highway trips only. It doesn't consume oil during normal daily driving. I can drive it daily for a month of driving (about 1,000 miles) and it doesn't use any oil but when I take a trip and drive 4-5 hours at highway speed it uses the oil. What could be causing it to use oil during the highway driving?
Thanks,
Jim
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Generally, oil consumption increases with power demands on an engine so this is a symptom --- of something.
If it were my car I'd check the PCV valve to ensure the crankcase venting system is clear and not allowing pressure to force oil past the valve guide seals. The valve guide seals would be the next suspect.
Suggest you consider a higher SAE weight oil i.e. 20W - 40 or 20W - 50.
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As far as I can tell it doesn't have a PCV valve. Does anyone know if it does and where it is located?
Thanks.

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Look up your w202 and appropriate engine at the following (go to the cars link - don't worry about putting in your VIN). You will find lots of exploded diagrams of all the systems.
http://www.detali.ru/cat/oem_mb.asp
Start at the section 14 for exhaust and intake manifolds.
Doug
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Thanks, the site is just as you indicated. I found 2 crankcase ventilation hoses but no valve. I'll check the hoses this weekend to see if they may be plugged.
Jim

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I will bet that it is using oil in town but fuel is being pushed past the rings and it raises your oil level. Then you take it out on the highway and the heat evaporates the fuel in the oil and all of a sudden you believe you are only burning oil on the highway trips.....
Are you using regular oil or synthetic oil?

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That's an insight.
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I've used synthetic since the first oil change. I normally make 2-3 hiway trips a year and everything was fine until a month ago.

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