Hello guys I am a new Bentley owner. I have had my car for 4 years with no issues. 3 months ago the check engine light came on and it would go off and on periodically. One day it started flashing and I noticed a miss fire so I took it to the Bentley dealer. 2 days later the told me I had low compression on cylinder 10, 11 and 12. The car only has 39k miles and has never had any problems at all in 4 years never ran hot or gave any signs of problems. I had the oil changed 4 month ago so it was good. The want $36,999.90 for a new engine. The never went into the engine to see why the only ran a compression test. I do hear a vacuum leak near the back top of the engine but I dont think it's big enough to cause such a misfire. To add insult to injury the company they recommend me to get it fixed cheaper says he is 5 months backed up. I need a good mechanic in Houston Texas and I am mechanically inclined I own a dealership so I was thinking possible a sticky valve???? I put seafoam in the oil and gas to see if it would help. Any suggestions??? In desperate need of Help

 

Actually, by quoting this silly number, they are telling you they don't want to work on it, I would be surprised if they actually dug deep enough to do a compression check.

Mr. "Five Months Backed Up" guy doesn't want to work on it either. Sorry to be cynical, but I'm sure I'm right.

First thing you need to do is to order this right away and get a read-out of all the codes it is throwing. Next, spend some time Googling and also bring the code readout back here, there are some absolute guys who have fallen from heaven that are experts and help for free.

If you really need an engine rebuild, it's going to be expensive, but not cray-cray $37k.

There's a whole engine for sale on Ebay for $7,500, add in $4k to change it and you're 1/3 the price of the dealer.

I bet you don't need a whole new engine, that's just worst-case.

Probably a simple vacuum leak. Still might be $5k to fix, but not the price of a whole car.

 

Also...there are lots of good independent shops across the country, once you have it diagnosed, if you need a top-end rebuild, just send it on a car carrier for $600 or $1,000, then fly out and drive it home when it's done.

My shop is good, but it's nowhere near Texas.

 

Please keep us posted if you have the time. I, myself, am brand new to the forum. Considering the purchase of a 2006 Flying Spur, and, please don't take any offense, but posts like this scare the hell out of me. Because, other than changing a flat tire, I'm not mechanically inclined. I will need to find a good indy shop near the Philadelphia area if I move forward on this car.

 

For suddenly the engine running on low compression..
I think something is funny here.. mechanical need time to wear out.. and if it wear out it will wear equally..
I think u need to check something there..

 

@Rico.Adams that is very rare situation unless something drop in the cylinder wall make it scratch...
because the car just run fine yesterday there're no reason it fail in the next day with mechanical issue unless we hear something very straignt noise...
I did rebuild alot of engine and I know that..
I think maybe
1st : they diagnostic it wrong
2nd : maybe it run low on oil all the time.. but this car has oil level warning sensor so I don't think it can happen

 

Which oil was put in 4 months ago ?
Compression loss is from either the rings have worn or maybe broken or valves not sealing .
Old school test If rings the pressure on the filler and dip stick holes would increase it’s called aptly “ blow by “
Valve s can be worn stems gunked up so they don’t fit back properly and gas gets around the poor seal .

Duff out of OEM spec oil could cause this .

 

I am a little suspicious. If the shop really did a compression check, the only way to do that takes a lot of mechanical disassembly. The intake manifold must be removed, new intake gasket installed. Did they do this for free? How much did they charge, what part(s) did they have on the invoice and we can then tell if they really did a compression check.

Second, what are the actual compression readings of all 12 cylinders? No compression check on an engine with any kind of mileage will yield 12 perfectly matched readings. Instead, you evaluate compression across all cylinders by % range highest to lowest, but first within an acceptable factory spec range.

Finally, if you really do have low compression in 10, 11, 12, these are the cluster of the last three cylinders on bank 2. With all of the suggestions so far, no one (I think if I read carefully) has mentioned a blown head gasket. That might be the first diagnosis...but color me suspicious overall.

 

@BWings I have a question about engine oil...
I ran 10W60 on my W12 and it sound really quiet.. for some reason I found the service hand boook it only said 12.5 liters.. but I saw some people here said 13 to 13.5 liter...I didn't have any oil minimum message warning or top up oil...
some people said I should run correct 0W40 ... too thick oil will damage the engine... is that true?
so.. next time oil change I should go with 13 or continue use 12.5

 

Hi NG,

I hope you are well.

12.5L is correct. Here in the US we use quarts. 12.5L = 13.2 qts. If you saw that in other posts, they might have meant quarts and not liters 12.5L is correct with a filter drain/change.

I would NOT use a 60 final weight in this engine. 10W60 is not a good choice. You are better returning to the 0W40 European formula oil as specified.

Many do not know this about oil final weight. The correct final weight is determined by the engine designer and based on bearing clearances. This is VERY important. If bearing clearances are tighter (closer) then a thinner final weight is required. A thicker oil will struggle to lubricate bearings properly. On the other hand, if looser bearing clearances are used, then a thicker oil is required otherwise, a thin oil will not hold oil pressure and fail to lubricate the bearings as well.

In the past, I've built several race engines. I would set bearing clearances "loose" then use a xW50 oil. This was popular with engines used in drag races where the engine would only be at full throttle for a short distance for only several seconds. These engines would not get too many runs before another rebuild. On the other hand, if you want an engine to last many more hours of runtime, bearing clearances should be more precise and much closer tolerance, but a thinner oil weight is then critical to proper lubrication.

So, running a 60 final weight in your W12, you risk starving bearings of oil. A spun or seized dry bearing would pretty much ruin this engine. The designers set clearances to lubricate best with a 40 final weight. This is your best choice.