Basic M40 Servicing

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Just got your first 4 pot E30?!

Don’t know when it was last serviced?

Scared of the Spanner?!

This guide was made for you!

The M40 engine is actually a really pleasant engine to work on, provided you follow these basic rules…

  • Respect it (bolts are more likely to shear if you hit the spanner with a sledge hammer!)
  • Stay calm and take your time.
  • Don’t get distracted. Keep Children, pets and nagging wives/husbands well away.

RHS=Right Hand Side LHS=Left Hand Side (sitting in driver’s seat)

Basic Servicing

To make your M40 purr like a kitty at idle, roar like a lion through the rev range, and scream like Steve Tyler at the limiter you'll need to give it the following treatment:

Coolant Change


  • 5L of Coolant (mix it 60/40 water/antifreeze)
  • Flat blade screw driver (for releasing coolant pipes)
  • 10mm socket (for thermostat housing)
  • Large Flat Blade screw driver for releasing bleed screw


1. Disconnect Battery

2. Loosen off and remove the cap on the header tank (at LHS of radiator)

Check the tank and cap for ‘mayo’ which is a sign that oil is mixing with the coolant (not good). Move the heater temp control to fully cold to prevent air locks in the heater matrix

Also check that the bottom is yellow and rated at 140. If not go to the dealer and get one. (they were subject to a recall years ago as the originals weren’t up to the job)

3. Undo bottom hose from radiator at RHS of the car, let coolant drain (catch it in a bucket and dispose of properly)

4. Undo the 3x 10mm bolts on the thermostat housing (at the front of the engine, in front of the distributor cap) (may need to remove small fuel hose to access one of the top bolts)

5. Remove thermostat, and check its ok (should be closed if cold) If in doubt an new one is £9.99 from GSF/ECP. Bolt housing back together.

6. Insert hose into header tank (at LHS of Radiator) and flush system until water is running clear.

7. Remove top hose (LHS) from radiator and flush through with hose until clear

8. Replace the thermostat, and reattach all hoses

9. Pour the coolant into the header tank (at LHS of radiator) SLOWLY and give it time to settle. (should take about 4.5l to get to cold level marker)

10. Set the heaters to full (HOT and no. 4 fan setting, open all vents) and start car.

11. Let the car idle for 5-10mins keeping an eye on the temp gauge

12. Open the bleed screw (next to the expansion tank cap) WATCH OUT FOR THE COOLANT SPRAYING!!!! (use a cloth to cover it!)

13. Repeat bleeding until all air is out and only water comes out when bleed screw is opened. Top up if required.

14. Get a cup of coffee and relax for 20 mins

Oil Change


  • 5L of engine oil (5w-40, 10w-40 or 10w-50 as recommended by Simon aka oilman)
  • GENUINE Fram oil filter (has all the non return valves etc, and worth the money)
  • 17mm socket + wrench (for sump plug)
  • Spark Plug Change
  • 4x Spark Plugs, preferably NGK brand (NGK BPR6ES)
  • Masking tape + pen
  • 19mm Spark plug tool

        • Wear latex gloves to save your skin****

1. Switch car off (oil should be warm so as much comes out as possible)

2. Go underneath car with 17mm socket and loosen the sump plug (make sure you have something to catch the oil!!!)

3. Remove oil filler cap and let car drain for 10mins.(can check how much is left using the dipstick)

4. Replace sump plug and tighten (but not too much)

5. Remove oil filter, (on RHS of block beneath exhaust)

6. Fit new oil filter (smear rubber seal on top with fresh oil to ensure good seal)

7. Remove oil filler cap (on top of engine) and fill SLOWLY with about 4.5l of oil (use dipstick to check level regularly)

8. Replace oil filler cap and start engine, allow to idle for 10 mins.

9. Check oil level again after leaving to stand for 10 minutes, check for leaks at the sump plug and filter, correct as required.

Spark plugs


1. Remove the Spark plug leads ONE AT A TIME and (using masking tape + pen) number them 1-4.

2. Remove the Distributor cap and check the condition of the Rotor arm and Cap (replace as required).

3. Inspect the leads for any sign of breakages/cracking.

4. remove the spark plugs ONE AT A TIME using the 19mm spark plug puller (may need an extension for plug 4 (nearest the windscreen)

Inspect the plug for signs of the car running rich (black soot), flooding (plug is immaculate as petrol washes it). Car running lean (Light brown/sand colour

5. Put in new spark plugs (put them in by hand until tight then ‘nip’ them a bit tighter with the puller) and refit leads

6. start the car and go for a well earned cruise

This article is copy write to E30zone and must not be replicated without prior permission. Written and photographed by Neil Purdom

[[[Category: Technical]]