THP engine maintenance
How to keep your THP engine healthy and happy
Keeping your THP engine healthy and happy is a simple process. All you need to do is follow some key points in its maintenance. We hope this guide will help extend your engine’s life.
Prince engine codes covered are EP6-DT, EP6-DTS, EP6-CDTX and EP6-FDTX. Or in the Mini world, N14B16AC and N18B16M0.
- Oxygen sensors
The oxygen sensors have a lifespan of 80.000km-120.000km and should be replaced while they are still working well. If not, they cause high fuel consumption and performance problems. The front sensor regulates mixture while the rear sensor monitors the condition of the catalytic converter.
- Pressure sensors
Prince engines have two pressure sensors: One on the boost pipe after the intercooler and one on the intake manifold. Both are exposed to oil fumes circulating in the intake system, which can eventually foul them. Cleaning them every 30.000km helps extend their life. The cleaner they are, the better they behave.
- Electronic control unit
In general, the engine control unit does not cause problems or produce faults by itself. However, there have been many reported cases of generation 1 ECUs (produced up to 2008) losing control of one injector. The engine starts misfiring and rattling when that happens, without any hardware problem. In case something like this happens, the first step is to get the latest ECU firmware update from the manufacturer and see if that solves the problem. In most cases it is just a hardware fault of the injector driver and the ECU needs to be replaced.
- Engine fusebox
The Peugeot 207 platform has major problems with the engine fusebox because it is prone to water damage. The fusebox by itself is well behaved. If the windscreen drains become clogged, the nearest exit point for water is through the engine’s fusebox. Protecting it can save you from a taxi ride home.
- Hydraulic chain tensioner
Does your THP engine sound strange in the morning at cold start? Do you hear the chain rattle until the engine warms up and then the sound is gone? The chain tensioner is to blame. It either gets stuck or its spring weakens over time. This results in the chain being very loose until oil heats up and you get good engine oil pressure.
Have it replaced ASAP. A bad hydraulic tensioner can cause the engine to lose its timing because of the unstable motion it causes at cold start.
- Loss of engine timing
Loss of engine timing is a very common problem in THP150 and THP156/165 engines. It is not common on THP200. Slipping cam shaft or crank shaft sprockets cause the engine’s timing to go out of phase. This causes a permanent retardation of the camshafts, resulting in high fuel consumption and sluggish engine performance overall. You can check “Long term fuel trims” (aka LTFT) via OBD2 to see if this is happening. If LTFT goes over +10%, there is loss of timing.
- Clogged intake valves
In direct injection engines the injectors sit in the cylinders. They do not spray the intake valves with fuel, like they do in traditional indirect injection engines. Whatever dirt and oil residues land on the intake valves will stay there, building layers of a thick rubber-like substance. The thicker these layers become they more the inhibit airflow around the valves and the more the engine loses its performance. You can read more on this in detail here.
This usually happens every 50.000-60.000km and the engine can lose as much as 20% of its power. It is a big headache because this is a mechanical problem: it cannot be detected with engine diagnostics because it does not show up as an error anywhere.
Remember to clean your intake valves as often as you can. It can extend the life of your engine and make sure it is working properly! There are many ways to do it without removing the cylinder head.
Although the thermostat is electronically controlled, its mechanical valve starts to under-perform over time. This leads to longer warm-up periods in the morning. It also leads to the coolant temperature going colder when travelling downhill or off throttle. Both these problems usually become evident after 70.000km. Replacing the unit fixes them. It is a good idea to replace the engine’s coolant every 2 year maximum, as it loses its rust protection properties.
- Ignition coils
The stock coils will generally not fail. They are very reliable. But make sure you never expose them to humidity or water and they will be good for life. If you wash your engine, remove the coils and let everything dry up completely before re-installing them.
- Spark plugs
Spark plugs should be kept no more than 30.000km on a completely stock engine. If you have a remap, it is advisable to renew them every 20.000km because you will notice a big drop in performance as you go over the 20.000km limit.
A good way to check their condition is by measuring spark gap. Stock spark gap is 0.8mm. The moment it goes over 0.9mm, ignition problems start to occur. For engines with a remap, we recommend setting the spark gap to 0.6mm. This will increase spark plug wear but will improve spark power by a lot.
Always stick to the manufacturers recommended spark plugs. As a rule of thumb, they are all made by NGK and are either made of Platinum (PLZ code prefix) or Iridium (ILZ code prefix). Anything else will just not do as only the heat range of Platinum and Iridium is suitable for turbo engines.
Iridium – ILZKBR7A-8G (Peugeot RCZ THP200, Citroen DS4 Racing THP200, Mini Cooper S Works Edition)
Platinum – PLZKBR7A-G (stock 150/156/165hp and 175hp)
- Burnt oil – Oil consumption issues
Ok, by now you have probably realised that THP engines consume a fair amount of oil. The usual oil consumption average is 1 liter per 5000km. Some engines consume less, some engines consume a bit more. This is very usual for direct injection engines and is no reason to worry. A part of oil consumption comes from the piston rings, a larger part comes from the valve oil seals leaking into the intake.
When your engine starts to consume oil, do NOT just top it up. Have the oil completely drained and replaced. Then wait and check your oil consumption again.
Most people just top-up engine oil, when the reason for oil consumption may be the existing oil quality degrading by itself. Bad engine oil quality means shorter life and the oil gets consumed faster.
If your engine starts to consume 1liter/1000km then you will need to check its compression. Then have the valve seals in the cylinder head replaced and everything checked by a specialist.
In terms of oil type, the most usual type is 5W-30, fully synthetic. If you live in a country with warm environmental conditions, you can probably use one grade thicker oil without problems. Colder countries can go down to 0W-30 without issues, as long as it is always fully synthetic grades being used.
- The stock fuel pumps, both high and low pressure, are usually good for 100.000km. They wear quickly when used in hot environments and they can be damaged by dirt in the fuel system.
Some THP low pressure fuel pumps, specially in African versions, come with an external fuel filter that can be replaced. It is a good idea to replace that every 20.000km. European versions have a filter built into the fuel pumps housing and it cannot be replaced.
- Stock injectors are usually good for life, unless the fuel system becomes contaminated with dirt or is left unused with fuel in it for a long period of time. Because they operate from 50bar to 120bar, it is easy for their nozzles to become clogged. While Peugeot and Citroen forbid ultrasonic cleaning, there are modern methods for cleaning and testing them, that work properly.
Be warned: A clogged injector can lead to a broken piston. It is a good idea to have them checked, measured and cleaned every 60.000km-80.000km.
- Cracked exhaust manifold
Cracks usually appear first inside and then outside the exhaust manifold. Very often we also see cracks develop on the twin scroll split. Eventually the manifold needs to be replaced before parts of it end up in the turbine. There is not much that can be done in terms of maintenance, just replace the exhaust manifold if you see cracks on the outside.
- Cracked turbing housing
It is very common to find hairline cracks in the turbo’s exhaust housing. The cracks start from the split between the twin scroll geometry and propagate outwards. There is not much that can be done to avoid them, it is just the material that is brittle and prone to cracking after 60.000-80.000km or so. Eventually the whole turbine housing needs to be replaced, or even the whole turbo if the turbine gets damaged.
- Oil consumption because of the turbo
Sometimes the turbo itself can be the reason for increased oil consumption. You can do a quick check to see if the turbo is losing oil by visual inspection of the compressor outlet pipe (on the cold side) and then the turbine housing on the hot side by removing the downpipe. If there are any signs of oil on either side, the turbo is leaking oil and needs to be serviced by a turbo repair shop. Or replaced with a new one. Do not leave it leaking oil!
These are just a few of the things we look in THP engine maintenance. Most checks are visual, some of them combine diagnostic tools and special tools. All in all, it is fairly easy to keep the engine in good shape.