Rattle on cold start V8 4.2

[davedonoghue]

I hear a sharp rattle on startup from cold which only lasts about a second, then I hear a noisy tappet for a further few minutes until it goes quiet and then the engine runs quiet all day. Once it has been idle overnight, it repeats the noises as before. I suspect either one of the VVT actuators or one of the VVT solenoids being blocked. Has anyone had this issue and if so do you have any advice for me?
Thanks.

[J44EAG]

It is unusual for the 4.2 to have cold start rattles, Dave.

The problems of the earlier plastic 4 litre V8 tensioners have at all intents been overcome on the 4.2 with the introduction of the 4th generation ali tensioners. That said, Rob J reported a problem where a sliper plate had parted company with the mounting plate atop a tensioner piston. That is the only case we have seen of there being an issue with a tensioner on this later 4.2 V8.

VVT units can get a bit of a cold start rattle due to wear but also blockage of the oil feed to the units. This is usually found on very high mileage cars where the oil change regime has not been kept up and long periods between oil changes have occured. Sludging of the oil ways can then occur. It is worth adding a can of Wynns Oil Flush twnety minutes before undertaking an oil change. Add the can to the oil and idle the engine without load before dropping the oil whilst still hot. You will be amazed how much oil sludge comes out once you have used the additive. That will certainly help break down the internal engine crud and hopefully allow a better oil flow to the VVT units. I would try that course of action before thinking about changing VVT units or deep stripping the engine. Halfords stock the additive for about a fiver.

I`m unsure whether the VVT units have a filter fitted. More research might be needed on that. In the meantime, try the flush additive and an oil change and let us know how you get on.

All the best,

Mike

[davedonoghue]

Thanks Mike, what you say fits with the symptoms. I will try the cleaner and oil change and report back.

Dave.

[robv12]

I'm going with Mike here, a blocked or lazy VVT unit, flush and flush again and see what happens

That said I have due here a blown 4.2 with a rattly top end, so will be interesting to see where the problem lies with this one, 2004 car, 174k miles, so there are all getting old and miley now, new problems will start to rear their heads

[davedonoghue]

Hi Rob, thanks for that. I will be doing the flush this weekend. Only worry is, will the flush cause other problems due to the cleaning action?
Dave.

[J44EAG]

An internaly clean engine is a happy engine. The flush is designed to break down sludge and gunge so that it comes out with the oil change. Oilways and drillings in piston ring lands will start to become clear of muck which restricts oil flow and leads to advanced early wear.

I`ve used engine flush for years and have never experienced any issues from doing so. As an aircraft engineer, I soon learned the value of keeping internal parts of an engine as clean as possible. We used to oil change every fifty hours of running time. That did the best we could manage for the engine. Car engines have a much harder life. Oil changing is nowhere near as pedantic as an aircraft. Consiquently, we need as car owners to do what we can to help an engine survive. Flushing on a regular basis will help maintain a gunge free engine. How can it possibly cause any subsiquent issues? Fresh oil after a flush will continue to clear gunge, so don`t be suprised if the new oil blackens fairly rapidly if engine flush has never been used before. You might consider dropping the oil again in a couple of thousand miles. It can only but keep up the good work.

Mike

Mike

[davedonoghue]

Thanks Mike, I will give it a try.

[davedonoghue]

Well, I have managed to sort this out without any repairs at all. By chance I had decided to try a product called 'Cataclean' as I was getting 'pinking' on hard acceleration accompanied by a cloud of smoke behind the car. So I put the 'cataclean' in the tank when it was down to 1/4 which is about 25 ltrs. Then I went up and down the motorway at high engine speed until all the fuel was burned. The next morning most of the engine noise that I had been hearing on start up was gone!! I doubt it had anything to do with the 'cataclean' more likely the hour or so at high engine speed and engine temperature has cleared an oilway somewhere.
So next as advised by Mike, I flushed the engine with Wynns engine flush followed by new oil and filter, now the noise has gone completely. Also, the 'Cataclean' seems to have been effective as the pinking has stopped and no smoke cloud behind when I boot it.
So thanks to everyone and in particular Mike who suggested the engine flush.

Well chuffed.

[J44EAG]

As others using this site will know, I`m a great fan of Cataclean. Its meritorious effects are fast acting and effective. I use the product once a year just before the MOT to ensure the cats work as well as possible when the car has its gas test. Cataclean often provides a very noticeable increase in low down torque which is felt by upward gear changes occuring sooner. As the fluid is induced via the fuel and the injection system, I suspect that it has also helped to clear some carbon from the combustion chambers.

Carbon build up can cause "pinking". This description implies signs of over advanced ignition or hot coal effect leading to dstructive detonation. That is not desirable as detonation is an uncontrolled explosion within the cylinders rather than a smooth even burn of fuel with a steadily increasing cylinder gas pressure as the ignited gasses expand to their maximum at optimum crankshaft angle. Detonation can lead to burned valves, damaged cylinder heads and holes being blown in pistons. Pre-ignition is another nasty caused by an overly large volume of hot glowing carbon coals withing combustion chambers. If that is the case, then clearance by major engine strip and coke removal might be necessary in extreme cases. However, the Terraclean process is very effective at removal of internal carbon and other combustion chamber by-products. I treated my XJR to a Terraclean last year and it very effectively cleared gummed injectors, released carbon and made the car more spritely. A five star recommendation for the process from me.

"Pinking" or detonation can also be caused by anti-knock sensor problems. Sensor failure of these slugs is rare but it is not unknown for sensor bolts to work loose over a period of time and comprome the effectiveness of these anti-knock devices. The sensors are mounted atop the engine with access being completely blocked on S/C engines by the supercharger. On normally aspirated units, access is rather easier. Anti-knock sensors are important as they detect detonation during periods of high engine load and high cylinder pressures. Their function is to signal the engine ECU that knock has been detected which leads to a forced retardation of spark plug timing as an engine safety feature. Use of low octain fuel of below 95RON value can also lead to pre-ignition issues especially if the engine has a large volume of carbon present in combustion chambers.

Moving back to oilway sludging, this is frequently to be found in engines which have had oil services neglected. Oil and filter changing must be carried out at least every ten thousand miles or sooner. In an unmaintained engine, oil sludge can build up very quickly even on low mileage units and even when using fully synthetic oils. Synthetics are less prone to sludgeand oil burn than semi-synthetics or traditional mineral products Higher mileage engines are prime candidates for increased sludge and this may well be an issue that has affected Daves engine. For your interest, I change my oil and filter every six thousand miles and always use a can of Wynns Engine Flush on those occasions. I use only K&N HP1014 filters which have high tech filtration media incorporated and have a repution for being one of the best filters available.

Daves car has a fair mileage on it now. It is an example that will indeed respond to Cataclean, engine flush and to the Terraclean process. Even at just 80k miles, my own car badly required all three processes applied to improve engine performance and to get the engine and catalytic converters back up to a higher level. I`d strongly suggest that a next step should be a Terraclean. My post on the subject is in the Engine section on this site and my article which appeared in the magazine can also be found on this site in the electronic back issues of our monthly journal.

Glad you sorted the problem, Dave.

Mike

[davedonoghue]

Yes thanks again Mike. I think my oil problem may be partly due to change intervals of approx 12000 miles compounded by continual slow speeds. I have commuted with this car for over six years ten miles each way through heavy traffic. I am a little disappointed to find that this lovely engine has suffered in this way as I always drive it sympathetically and always use good quality oil. However I shall reduce the oil changes to 6000 intervals and use the flush each time in future.
I still think it is a brilliant car and will buy another when this one gets too old.

[J44EAG]

I have a close friend who is an industrial R&D engineer with a string of qualifications....one of them as an MSc transmission man. He commutes weekly from one end of the county to the other in a Merc diesel. This obviously gives "good" motorway miles as oposed to a daily "bad" mileage of just ten miles in slow conditions. That is likely to give oil a real hammering especially if not a premium product. His continued obsrvation is that he uses Mobil 1 as his prefered oil followed by Castrol Edge. Neither are cheap products.

Perhaps the answer to some of the sludge issues is indeed to use only premium oils.

Yesterday I changed my oil and filter. My favourite K&N HP 1014 filter fitted and Titan fully synthetic added. The old use sythetic Wilko oil was vintage 6k miles with flush additive for twenty minutes. The oil was not overly black but some minor treacle dropped into the tray when I cracked the filter off. No much, just a little. I emptied the oil from the filter which suprised me with its weight. Rather hreavier than a replacement identical filter. I think I`ll cut the filter open tomorrow and see what lurks within!

Mike