Oil Analysis blues

InIdaho · Mar 14, 2008

Trying to check out a used truck with a MBE 900 (300 hp) engine with lo mileage.

Had Freightliner do a 2 hour inspection, pulled computer codes, all checked out ok. Codes showed a high idle percentage (54%) but truck has no apu.

Had dealer pull an oil sample and they recommended a local lab to take it. The lab found elevated Iron 31.6 ppm & Aluminum 45.2. At my request they retested with same elevated levels. Darn now what?

Took truck to Speedco they pulled a new sample. Sample tested OK normal wear on all metals. Numbers even matched very close to the seller provided reports from the last 2 oil changes in June & December of 07.

Still at Speedco, decided to have them test the left over oil tested at the Lab. Wouldn't you know, it doesn't show any elevated iron or aluminum (<5 ppm & 2 ppm). Who to believe?

What you think? Send out the remaining Speedco drawn sample for a third opinion?

astikhossw · Mar 14, 2008

Why not just ask the service manager what he recommends.

piper1 · Mar 15, 2008

That's the problem with one off oil samples. Oil samples are best used to look for trends.

Take the last sample to a CAT or Detroit dealer. See what it says.

If you feel at all uncomfortable walk away. You'll never feel sure about that motor if you have doubts and you'll start thinking you 're hearing things and worrying.

At 54% idle I'd be scared.

nightcreacher · Mar 15, 2008

Be careful with the oil samples at speedco,there machine is not that accurate.As was stated,oil samples are to follow a trend,those levels might have been high from day 1.good luck

InIdaho · Mar 15, 2008

Going to send what is left of the sample we saw drawn at SpeedCo to blackstone Labs.

The 54% idle time caught my eye too but the dealer said it was nothing to sweat. Why might I be concerned with a high idle time?

piper1 · Mar 15, 2008

When an engine idles that much things cool down and may not be optimum. Prolonged idling can result in low oil flow to the top of the engine and lead to top end problems. Pistons shrink a bit when they aren't at operating temp so they don't always run as true. Fuel wash into the motor oil happens with prolonged idling resulting in bearing wear and cylinder wall wear.

Bottom line nobody builds a motor to idle that much so it suffered some harshness.

If you can, run the engine until warm (drive it a few miles) and then at a 1000 rpm idle open the oil filler cap and see how much it huffs out. It will puff a bit of fumes (all engines do) but it shouldn't be enough to blow off a paper coffee cup. (that sounds scientific eh?)

Moot · Mar 15, 2008

An important factor in oil analysis is how the sample was acquired. Also traces of aluminum and iron could be left over from the manufacturing process.

nightcreacher · Mar 15, 2008

The new electronic engines dont need the warm up like the old engines,and cool down either.just dont put a load on the engine til it warms,but run at parcial throttle when you leave on a cold engine.To me 54% is a lot of Idle time, tractors that pull a tankers,have that kind of idle time as they are running a pto

InIdaho · Mar 15, 2008

What would does the amount of huff point too/indicate?

InIdaho · Mar 15, 2008

Could any additives mask aluminum and iron such that one method of analysis used by one lab would see the metals and another testing protocol such as what Speedco uses miss it entirely?

RLENT · Mar 15, 2008

Blowby from the combustion chamber past the rings into the crankcase ?

InIdaho · Mar 15, 2008

Would blowby mean also ring wear and higher chromium readings? It was lo in all reports.

astikhossw · Mar 15, 2008

What is the year of this truck and how many miles or on it, i mean if this is an older truck with high mileage it could make differance.

piper1 · Mar 15, 2008

Blowby or huff indicates poor cylinder sealing (rings or cyl wall). Chrome readings may not be high as chrome ring surfaces can be more wear resistant than the iron cyl wall. The cylinder walls can get "polished" with a lot of idling or poor oil maintenance. When this happens it will huff and burn oil. Aluminum and iron can mean piston skirt and cyl wall wear is occurring.

Oil additive metals are usually zinc, phosphor/phosphate, and molybdenum among others.

If the engine is low mileage and it has this much idle time and these oil conditions..........

How good is the deal on this truck?