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Old 3rd August 2011, 23:14   #19
Robson Rover Repair
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Default CHAPTER 12 - Overview and common faults for the diesel engines

Diesel M47R Buyers guide / problems, costs and general engine information overview

This guide covers the ESSENTIAL issues with M47R diesel engine in 2.0 115 and 131 outputs as the issues with them are all common regardless of power output.

A history of the M47R

You will always hear people saying that the Rover 75 /MG ZT has a BMW engine, well thats only true if it has a diesel engine in the car. The 2.0 litre diesel unit was BMW's common rail motor, designated M47R.

M47R used in the 75/ZT was was based on the early 1998 - 2001 BMW "M47D20" diesel engine except mildly de-tuned compared to the power outputs that BMW had.

Whilst it had the same core engine block it had many parts redesigned for the front wheel drive gearbox and transverse fitting into the engine bay.

For example, in the BMW 320d's of the time, the engine was notoriously unreliable, yet the diesel 75/ZT version suffered none of the common problems. Chief among the BMW 320d cars problems was a 'swirl flap' mechanism employed within the inlet manifold. These consist of a number of butterfly valves within each individual inlet tract. Unfortunately these flaps are secured to an actuating rod via 2 small screws.

When this happens they can end up being drawn into the respective cylinder causing significant damage to both piston, cylinder head and valves. If unlucky further damage can be caused to the turbo if the screw then makes it's way through the exhaust valve into the manifold and subsequently into the turbo.

So much for the "ultimate driving machine" and yet another example of peoples foolishness that assuming certain brands are better cars by the badge.

Back to the M47R fitted to the 75/ZT, the engine was available in two power outputs (115 bhp and 131bhp details covered below) and does not suffer the kind of service and maintenance bills that the KV6 has, however there are common faults to watch out for and they have been listed below.

M.P.G

Arguably the main reason for purchasing a diesel 75/ZT would be the fuel economy that the car can produce. Listed at the bottom of this is all the "official" MPG figures and stats for all the engines, in various powers with the various gearbox types.

It is safe to say that you will comfortably get a minimum of 40 MPG out of your diesel engined car. Now do not panic, I said a minimum. More realistic for everyday driving is a solid 50mpg with the automatic gearbox and a 55ish MPG for the manual gearbox.

Again driving style s the biggest factor but engine condition is essential on the engines for keeping the MPG up, and the common faults (listed below the Power Output section) will help explain what is wrong if your MPG figures are perhaps not so good as you hoped.

Power Outputs 115/131bhp

As both the 115 and 131 engines are totally identical bar the electronic control mapping (the ECU), they will be treated as a single engine in this section specific to them and specific faults to watch for.

Cars are badged as CDT and CDTI but that does not mean a CDT is 115 or a CDTI is a 131bhp engine. The 8th Chassis number should be "H" but that doesnt change for either power output.

THERE IS NO GUARANTEE A CDT OR CDTI IS ALWAYS A 115 OR A 135, UNLESS THE LOG BOOK STATES 135. Please remember this to avoid disappointment.

Any X-part dealership with a T4 Rover Diagnostics machine can change the ECU map for you. If you have the remap it should have a sticker on the B pillar on the drivers side of the car about a third of the way up.

[CENTER]

This is not always guaranteed however, so check the logbook as it will state 115 or 131. If you wish to upgrade your 115 to a 131 (which is highly recemmended by all owners), it will cost you £199 plus an hours labour at around £35.

This remap is sometimes referred to as ''the X power remap'' and was a Rover / MG optional extra and should not cause you any problems with your insurance once declared as they simply see you car as being a 131 model instead of the 115 model.

More power is available from tuning the diesel engines, up to 170ish bhp with various modifications and searching the forum will help you find guides on parts and fitting and costs.

Common faults of the Diesel M47R engines

Oil leak at radiator

A annoyance but a common fault as it will happen to every car at some stage, when the intercooler "o" rings fail and they do all too often then there is always an oily mess at the front passenger side under the bonnet. It is hours work maximum job to replace them and fortunately there are upgraded "viton o rings" that can be purchased. For maybe 100 users that comment on this leak, only 1 would need an inter cooler to be replaced and thats usually when they have neglected it for a very long time!

The DIY repair guide to this can be found here... https://www.the75andztclub.co.uk/for...ad.php?t=81279


Cam chain rattle

The diesel engine uses a cam chain, rather than a timing belt mechanism. Cam chains usually do not require replacement unless they become loose and noisy.

If there a rattle noise (like nails in a washer machine) when the engine is ticking down in the driver’s side of the engine bay then more than likely this is the issue and then it is likely the cam chain has stretched.

The cam chain is inside the engine and replacement is very labour intensive as the chain was designed to last the life of the engine. This is not a "common fault" as such, but it is perhaps the first most easiest fault to diagnose when you first examine the car.

Sluggish at low revs

People used to say diesels where slow, this is very untrue of a healthy 75/ZT diesel engine. Providing quick and brisk acceleration that would embarrass most boy racers!

Typically you wil find that if the engine is sluggish from lows revs around 1250RPM in all gears then it is likely a simple cause. The MAF (mass air flow sensor) is past its sell by date and will need replacing, this can be expensive depending where you purchase a replacement.

The best way to test this is to disconnect the MAF and then start to drive the car, you will find the power increases immediately and that will be your solution. You should not however drive the ca like this for any distance as it may cause serious engine damage if left disconnected continuously.

Prices of £130 wouldnt be unheard of, which is shocking when you can buy similar ones from ebay much cheaper. A lot of people simply remove it, and clean is, and refit it!

The alternative is a MAF from another car with a MAFAM compensator. This forum is filled with discussion about the matter and anyone who does it will recommend it.

Excessive Black Smoke / Poor MPG

Again, as the cars warm and when you accelerate, you might notice a small whisp of black smoke. This is normal, however you may notice a trail of smoke under heavy acceleration and this is usually a warning sign that either the MAF has failed (as above), or is over fueling the engine (again, clean or replace).

Also, the Exhaust Gas Recycling valve (EGR valve) after a few years of driving is likely to be restricted due to being blocked by sooty and oil vapour and deposits blocking the airflow. The EGR needs cleaning or replacing or bypassing.

The benefits of bypassing vary, as it means its zero maintenance in the future, and some owners report the cars idol gentler. Again, ask opinions on the forums and where to purchase the by pass.

Dip Stick test

A simple test that can show a engine on its way out. When the engine is running, does oil spit out of the top of the dipstick pipe when the dipstick is removed?

If yes, you have a problem that could be serious. The PCV (positive crank case ventilation valve aka oil filter) hasnt been changed in time with the last service, or with recent services and needs sorting asap.

Do not attempt to clean the filter, it must be replaced and everytime an oil change is done after that.

If this is left unattended for long periods serious engine damage can occur. A blocked PCV valve will cause the oil to be expelled out of the dipstick tube when the engine is running and this can cause serious engine damage.

Fuel pumps

There are two fuel pumps on the diesel cars, the inner one (which is below the passenger rear seat, you hear it buzz when you put the key into the ignition to start the car), and the under bonnet pump, under the car bonnet obviously.

These seem to just wear out over time, millage reports are inconsistent but costs of replacing them are not sadly.

If the in tank pump can’t be heard to have a quiet buzz above the rear seat it is likely the in tank pump has failed, this causes the under bonnet pump to fail as it has to do all the work to pump the fuel. The under bonnet pump will make a large amount of buzzing ad noise hen it is doing the work of both pumps and thats the sign its also on its way out.

You can simply check both the pumps using this method given by Jules our resident expert on everything!

There's no need to lift the rear seat to hear the intank pump as most people think.
Disconnect the under bonnet pump (if one fitted) by pressing tab on the 2 wire plug which just pulls away then.
This isolates the front pump so there is no confusion between which pump you are listening to.
Providing the surrounding noise level isn't too great, open the fuel flap and stick your ear around the filler neck.
The Intank pump can be heard quite clearly for 50 seconds then switches off (Ignition ON engine not running)

Same 50 seconds test applies to underbonnet pump also after it had been re-connected

Diesel Thermostat

Simply the diesel engine runs best when up at full temperature (eg on a long motorway drive, or puling a caravan), and short driving/inner city driving wont allow the engine to get up to correct temperature to get your MPG to the best. Many report between 6 to 8 miles before the engine is up to full working temps.

Without boring you with science, it is simpler to explain that the diesel engine is very efficient at keeping cool. Too efficient unfortunately, this has lead to many diesel cars suffering a thermostat failure (it getting stuck open or stuck closed).

If the thermostat is closed, then there is no water going to the radiator, and it doesen't matter how good or bad the radiator is. The only cooling you will have comes from the heater matrix, if it is open, and from cooling around the engine as well as from heat lost in the exhaust.

Obviously, a stuck thermostat in an open position will make matters worse. As you then have an amount of water being cooled because of the radiator.

One simple solution to this is actually the OEM full burning heater, (which can be remote controlled) which will preheat a diesel engine for you for a few minutes before you begin your journey. This is especially useful in the winter as not only is your car defrosted from the heater being active, but the car is nice and warm on the inside.

The downside of this, is a hit on your MPG but only as much as you use it.

Many people are replacing their thermostats with ones from a Renault 5 now, details can be found here how to DIY it. https://www.the75andztclub.co.uk/for...ad.php?t=74451

Correctly reading the oil dipstick

A false LOW reading seems to be obtained whenever the dipstick is left in place after running the car and returning home. Even reading the dipstick the morning after with the engine now completely cold, the first time the stick is extracted will give a false LOW.

On wiping and re-inserting immediately afterwards , a correct FULL reading will be obtained. Also, If the dipstick is taken out and left on top of the engine whilst in the garage, then on reinserting a correct FULL reading will be obtained. Similarly ANY reading taken after first removing the dipstick and re-wiping will be CORRECT.

General servicing costs and maintenance

So if all of that hasnt scared you off then heres the good news now, assuming you have covered all the regular issues listed then actual maintenance of the diesel engine is actually quite inexpensive providing you service it when you should.

Depending on usage, a 12,000 mile service is perfectly acceptable, some do around 6000 miles if the car is used less frequently, but its up to yourself.

The basic oil filters, engine filters and such are quite cheap, changing everything will cost you no more than £50 and the dearest thing is actually the glow plugs which are £20 ish for all four.

Use of the correct coolant is recommended so use O.A.T coolant, which is pink in colour. Save yourself over Halfords prices and buy none-diluted from your local Vauxhaul dealership. 5 litres will cost you about £22 maximum and when you mix it 50:50 gives you 10 litres of coolant.

Use a 10W/40 or 15W/40 oil meeting both ACEA A3 and ACEA B3:96 specifications, and having a viscosity band recommended for the temperature range of your locality.

Additionally, many owners have reports that especially when they top up their diesel engine with some 2 stroke oil into the FUEL TANK with your diesel (roughly 1ml for every litre, or 50ml per tank full roughly) the car behaves and starts much easier. Perhaps a refection of the high sulfur levels in modern diesel for sale on the forecourt.

Last edited by Robson Rover Repair; 16th July 2022 at 13:53..
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