The N62 V8 sits in the 2004 to 2010 E60 545i and 550i, E63 645Ci and 650i, E65 745i and 750i, the E53 and E70 X5 4.4i and 4.8i, and the 2002 to 2005 Range Rover V8. Its valve stem seals are a known weak point: small rubber seals at the top of each valve guide that harden and shrink with age and heat until oil leaks past them into the combustion chamber and burns. Thirty-two seals, two heads.

The conventional repair gets to those seals by removing the cylinder heads. On a V8 that is a multi-day job with a great deal of labour before a single seal has been touched, plus head gaskets, timing and everything that has to come off to reach the heads. That is why the quotes run into the thousands, and why so many N62 owners live with the smoke or sell the car. This page will not quote you a workshop figure, because it varies with the garage and what else they find, but every N62 owner who has asked for one knows the shape of the number.

What the quote buys you is a permanent fix with a warranty and no weekend lost. That is worth something, and for an owner with no tools, no space and no wish to learn, it may be the right route. The other two are for everyone else.

The AGA BMW N62 valve seal tool was designed to make seal replacement possible without removing the engine, the cams, the heads or the timing. It feeds compressed air through the spark plug hole to hold each cylinder's valves closed while the spring is compressed, the old seal removed and the new one fitted. The only parts that come off are the rocker covers, which is a straightforward job on the N62. Phil found the tool when his own 650i started smoking in 2015, fixed his own car with it, and has hired it out ever since.

• £220 for seven days, complete AGA tool kit Everything needed to compress each valve spring, remove the old seal and fit the new one with the heads and cams in place. Special Delivery to you is included; you pay the return postage on the kit.
• £550 with the complete Elring seal kit The tool hire plus every seal and gasket for the top end: 32 Elring valve seals, 2 Elring rocker cover seal kits, 2 cam chain cover oil seals, 2 eccentric sensor seals and 8 spark plug tubes. If you are in there, do the lot.
• How-to video and Phil on the end of an email The full walkthrough video from rocker covers off to new seals in is included, and Phil is available throughout the hire. He has done this job himself and will talk you through anything you are unsure about before you commit.
• What you bring Basic mechanical competence, a weekend, a source of compressed air for the tool, and the normal hand tools to remove and refit the rocker covers. If you can remove rocker covers you can use this kit.
• What it is not It is not a tool for other engines. Phil's compatibility list is the N62 cars above plus the 2002 to 2005 Range Rover V8. If yours is not on it, ask before hiring.

The timing chain is never disturbed, the engine stays in the car, and a job that was a major engine rebuild becomes a careful weekend project. Full details, the video and the vehicle list are on the tool hire homepage. The hire terms, what is in the kit and how to book are on the tool hire page.

The same criteria for all three, with the Forte and hire columns taken from Forte's product information and Phil's hire terms.

The sensible order for most owners is bottom to top: the additive for a month, the tool hire if the smoke is still there, the workshop only if you cannot or do not want to do the job yourself. Phil will tell you plainly which he thinks fits your car; he has no interest in hiring a tool to someone whose seals would have responded to £18. The Forte Seal Conditioner page covers the companion product and when to add it.

Four signs, and most smoking N62s show at least three. A puff of blue smoke on startup, especially after sitting overnight, because oil has drained down the guides past the hardened seals. Blue smoke on the overrun, when you lift off at speed coming off a fast road: the high manifold vacuum draws oil past the seals, and Phil considers it the most definitive valve seal sign. Higher oil consumption, needing top-ups between services. And a garage quote in the thousands that named the seals.

Worn seals rarely set a code on their own, but the oil they let burn does. P0420 and P0430, catalyst efficiency below threshold, one per bank, is the N62's signature secondary code, because the burning oil cooks both catalytic converters. P0301 and P0308 single-cylinder misfires appear when oil pooling on one cylinder fouls its plug, often after an overnight sit, and P0300 random misfire when several cylinders are affected. BMW's own fault memory, read with INPA or ISTA, often logs rough-running codes such as 2A82 and 2A87 for the same cause.

If you want to be sure before spending anything, the five-minute test on the blue smoke page separates seals from rings and breather with no tools. Then send Phil your codes and symptoms. He will give you an honest read on whether it is valve seals, and whether to try the Seal Conditioner first or go straight to the tool.