The 1.6-litre THP engine in the BMW 1 Series suffers from structural issues which, if neglected, lead to severe engine damage: increased oil consumption, contaminated inlet valves, defective injectors and a stretching timing chain. This article explains what you need to look out for as an owner and how to prevent expensive repairs.
Common THP engine problems
The THP engine was developed in cooperation with car group PSA (Peugeot and Citroën) and is found in the BMW 116i, 118i and 120i models of the F20 and F21 generations. BMW versions perform slightly better than their French counterparts. However, the same structural weaknesses remain visible.
The first warning signs appear around 80,000 kilometres. Increased oil consumption tops the list. Owners report usage of 1 to 4 litres per 1,000 kilometres. This is caused by contaminated oil scraper rings (components that scrape oil off the cylinder wall) and poor valve stem seal sealing. This oil consumption can rise quickly and, if neglected, lead to total engine failure.
The timing chain stretches or breaks due to wear. You will hear this as a rattling noise on a cold start, sometimes accompanied by a fluctuating idle speed. This disturbs the timing. It damages valves and pistons.
How do I fix oil thirst in a BMW 1 Series THP engine
Increased oil consumption demands strict maintenance. Change the oil every 10,000 to 15,000 kilometres using the specification prescribed by BMW, such as 0W-30 or 5W-30. Check the oil level weekly once you pass 80,000 kilometres.
Inlet valves become contaminated due to direct injection. The fuel does not wash the valves clean, causing carbon deposits to build up. These deposits reduce the size of the intake opening and cause hesitation and loss of power. Walnut blasting removes these deposits every 50,000 to 80,000 kilometres. This is a cleaning method in which walnut shell granules are blasted under high pressure to clean the valves. This prevents further issues.
Practical tips to keep oil consumption under control:
- Use high-quality engine oil with the correct viscosity
- Change oil and oil filter more frequently than the standard interval
- Check the oil level at every fill-up
- Keep a log of oil top-ups to spot trends
Symptoms of defective injectors in BMW 1 Series 116i
Defective injectors manifest themselves through irregular idling and an uneven-running engine after starting. The engine may hesitate while driving or lose power under acceleration. Sometimes there is smoke or you can smell unburnt fuel.
Injectors become contaminated by deposits of dirt and fuel residues, and by poor fuel quality. This leads to incomplete combustion, which directly affects performance. Cleaning the injectors can offer temporary relief, but in cases of serious contamination they will have to be replaced.
Watch out for these warning signs:
- Ticking noises from under the bonnet when starting from cold
- Increased fuel consumption without any clear cause
- Orange engine warning light on the dashboard
- Black smoke from the exhaust
- Rough engine running at idle
Hydraulic tappets and oil circulation
Ticking hydraulic tappets are a frequent issue with the THP engine. This noise is caused by poor oil circulation to the tappets, giving them too much play. Replacing them solves the symptom. The underlying cause often lies in deterioration of the oil quality.
Some owners report that the ticking disappears after a thorough oil change using a slightly thicker viscosity. However, this only masks the problem temporarily and does not resolve the wear.
Timing chain replacement and prevention
The timing chain requires preventive maintenance between 100,000 and 150,000 kilometres. Do not wait until the chain breaks, as this will cause internal engine damage due to contact between valves and pistons. Replacement costs are between 1,500 and 3,000 euros, depending on the workshop and any additional damage.
Rattling noises on a cold start indicate a stretched chain. Have this checked immediately by a specialist who can measure the chain tension and wear. If in doubt, always opt for replacement, because the cost of engine damage is many times higher.
The chain stretches due to normal wear. Contaminated oil or too little oil accelerates this process. This reinforces the importance of regular oil changes and checking the oil level.
‘ A defective turbo needs to be replaced, which means an expensive repair. ’
Turbo and cooling problems
If neglected, the turbo fails between 60,000 and 100,000 kilometres. This shows up as loss of power, increased oil consumption and sometimes a whistling sound during acceleration. A defective turbo needs replacing, which means an expensive repair.
The water pump fails at around 80,000 kilometres. This leads to overheating and, in severe cases, cylinder head gasket leaks. Regular inspection of the cooling system prevents these problems. Watch for leaks under the car and check the coolant level regularly.
Is the THP engine recommended for a used BMW 1 Series
Buying a used BMW 1 Series with a THP engine calls for caution. Avoid pre-2015 models without a complete and documented service history. The risk of hidden problems is considerable in these cars.
Post-2015 models have the three-cylinder B38 engine (an economical three-cylinder petrol engine) or the N47 diesels (four-cylinder diesel engines) with an upgraded chain. These offer greater reliability. If in doubt, choose these alternatives over the four-cylinder THP version.
When viewing a car, check the following points:
- Start the engine from cold and listen for rattling noises
- Check the oil level and the condition of the oil
- Ask for documentation of servicing and repairs carried out
- Test the engine for hesitation while idling
- Watch for smoke under acceleration
- Check for oil leaks underneath the engine
Maintenance costs and budgeting
Budget for higher maintenance costs with a THP engine. This engine needs extra attention:
- Timing chain maintenance
- Walnut blasting of valves
- Potential turbo repairs
Owners who follow this strictly sometimes reach 280,000 kilometres without major issues.
Neglect quickly leads to expensive repairs or even replacement of the complete engine. The balance between purchase price and future maintenance costs therefore deserves thorough consideration.
Practical recommendations for owners
Regular maintenance keeps the THP engine reliable. Choose a workshop with experience of these engines, preferably one specialising in BMW or PSA products. They recognise the typical problems sooner and can advise preventively.
Use the car regularly and avoid short journeys. On short trips the engine does not reach operating temperature. This promotes condensation in the oil. That speeds up wear. Longer journeys help keep the engine clean and reduce the risk of contamination.
Watch out for early warning signs such as changes in engine behaviour, unusual noises or increased consumption of oil or fuel. Early detection prevents small problems from turning into serious damage.
On the Carnews website you will find much more information about BMW models, common car problems and practical maintenance tips. Discover more articles and expand your knowledge about the reliability and maintenance of your car.
Frequently asked questions
The THP engine in certain BMW 1 Series models mainly suffers from increased oil consumption due to contaminated inlet valves and worn piston oil scraper rings. In addition, the stretching or even breaking of the timing chain is a well-known problem, recognisable by a rattling noise on a cold start and an unstable idle. Internal contamination of the intake tract and carbon build-up are also common, leading to loss of power and a hesitating engine. Furthermore, defective turbos and issues with the water pump and cooling system are reported weak points.
Common causes of THP engine problems in the BMW 1 Series are increased oil consumption (due to contaminated inlet valves and worn piston oil scraper rings), a stretching or breaking timing chain, internal engine contamination and defects in the turbo and cooling system. These can be recognised by a rattling noise on a cold start, a fluctuating or unstable idle speed, a hesitating engine and noticeable loss of power. A sharply rising oil consumption (having to top up regularly) and any warning lights for engine or cooling are also warning signs. Timely inspection and cleaning (for example walnut blasting) and preventive replacement of the chain help to prevent serious engine damage.
Owners can limit THP engine problems by changing the oil more frequently than factory-prescribed (every 10,000–15,000 km) using the correct, high-quality oil, and checking the oil level weekly from around 80,000 km. At any rattling sound on a cold start or irregular idle, have the timing chain checked immediately and, if necessary, replace it preventively at around 100,000–150,000 km. Have the inlet valves cleaned periodically (around every 50,000–80,000 km), for example by walnut blasting, to prevent carbon build-up and loss of power. When buying, it is wise to choose a car with a full service history, start the engine from cold to listen for rattles, and avoid older, poorly maintained THPs.
The average repair costs for the notorious THP engine issues in a BMW 1 Series are roughly between €1,500 and €3,000 for a chain kit, and on top of that, cleaning (walnut blasting) and possible turbo/cooling repairs can add several hundreds to well over a thousand euros extra. For cars with poor or unknown maintenance, the total bill can quickly approach or exceed €4,000, especially if there is already engine wear. The investment is only worth considering for a demonstrably well-maintained car with a full history and if you plan and budget for preventive maintenance. In many cases, a car with the newer B38 engine or an alternative model is the more sensible choice economically.
There are partially reliable solutions, but no “definitive fix” that completely eliminates the THP’s weak points. Well-known measures include preventive replacement of the timing chain, regular short oil change intervals with quality oil, and periodic walnut blasting of the inlet valves. This can significantly improve lifespan and reliability, provided it is carried out by a specialist with THP experience. However, the design weaknesses (such as the chain and oil consumption) remain a risk, especially at higher mileages.