CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2005 Grand Prix Oil Usage

Hello Everyone,

I’m looking for some advice on my 2005 Grand Prix GTP. It has the 3.8L, supercharged V6. It currently has 109k miles. Since it turned past 105k miles, it’s begun to use oil. So far, it’s used 3 quarts in 4,000 miles. I am taking it to be looked at next week, but there is no evidence on the garage floor that there is an external oil leak.

Does anyone have any advice on what could be going on, or how to fix it?

Thanks!

That’s not something to be worried about. Most auto manufacturers consider a quart consumed over 1,000 miles to be normal. And that’s on their NEW engines.

Tester

It sounds as though the oil consumption started at your last oil change. As tester pointed out, you don’t have anything to worry over, but you might try a different brand of motor oil at your next oil change. Sometimes, certain brands of oil seem to burn off more quickly than other brands in a particular make of car. At any rate, be sure to use the viscosity of oil specified in your manual.

A clogged or sticking PCV valve will increase oil usage, it’s cheap and usually an easy replacement. Also check the oil pressure sending unit for a leak.

Ed B.

Actually, it started prior to the last oil change. I had to put in 2 quarts over 3,000 miles, and 1 quart in 900 miles after the last oil change.

I’ve been using the same brand of oil over the last 80k miles, and never had to put in more than 1/2 quart in between oil changes.

I will have the check the PCV valve and oil pressure sending unit. Thanks for the suggestions.

Assuming no PCV or external leak problem, the first step after that should be to run both a dry and wet compression test to verify any potential piston ring problem.

One murky area here is the propensity sometimes to call a lower than normal reading a good one. Even the specs printed in many service manuals is incorrect and some mechanics buy into that erroneous information.

“The light that burns twice as bright only burns half as long”…Force-feeding a V-6 so it acts like a V-8 takes it’s toll…

Caddyman, I assume you are implying abuse to the engine because it’s got a supercharger? That’s a pretty bold assumption…

The 3.8 is one of the best engines that GM ever built and using a quart of oil every 1000 miles is not normal unless there’s a problem. Car makers state things like this are normal because they’re faced with a grim reality; spending countless billions of dollars replacing engines under warranty.

For what it’s worth, my son has a 3.8 in his Camaro (Also a Buick engine) that uses about a quart every 1k miles but at 14 years of age and a quarter of a million miles it can be expected. That oil consumption is also due to a very visible leak at the rear main seal which he just flat doesn’t want to mess with at this time. If it wasn’t for the main seal oil useage would be near nil.