Why do I need to perform an engine oil flush?

What Types of Engines Can Benefit From Using an Engine Oil Flush

It can be used on all types of engines including LPG, diesel and petrol. It is important to follow the oil flush manufacturer's instructions/recommendations/warnings on the side of the bottle.

When To Use an Engine Oil Flush

Use the engine oil flush whenever you are doing an engine oil change. It is the first step before changing the oil. The flush is poured in with the old oil and helps loosen up contaminants, sludge and deposits so they can be flushed out when the old oil is drained.

General Steps To Using an Engine Oil Flush

1. Warm Up the Engine:
Start your vehicle and let the engine run for a few minutes to reach its normal operating temperature or take it for a short drive. This warms up the old oil. When up to temperature turn off the engine.

• Note: - While doing this initial warm up, leave the car parked where you want to drain the oil

2. Adding the Engine Oil Flush:

• Locate your engine oil filler cap (usually on top of the engine) and remove it.
• Pour the recommended amount of engine oil flush into the oil filler and replace the cap

3. Run the Engine:

• Start the engine again and let it idle for the time specified on the engine oil flush product label (typically 5-10 minutes).
• Do NOT drive the vehicle during this time, only let it idle. Driving the car with oil flush in it can cause engine damage.
• This idle time allows the flush to circulate through your engine and break down deposits.

4. Drain the Old Oil: After the specified idling time, turn off the engine and drain the oil immediately or as soon as possible.

• You need to do this before the engine has time to cool down and the contaminants swirling around in the oil have time to settle
• You need to be careful as everything will be hot to touch so gloves and some forward planning to allow easy access to the sump plug is vital to avoid burns
• Allow access for the tray to catch the oil and let the old oil fully drain as much as possible

5. Continue with the Oil Change

From this point on the oil change continues as normal. Replace the old oil filter with a new one and add new engine oil. Never leave the old oil filter on the engine after doing an engine oil flush.

High Mileage or Neglected Engines

There is a lot of for and against on using an engine oil flush on high mileage and neglected engines. Neglected means the engine has not been serviced when it should and that there has been long intervals between oil changes or worse, no oil changes. Both can have a high level of contaminate build up and when the oil flush loosens it there is a possibility of larger pieces floating around the engine. The oil flush is not in the engine long enough to dissolve or suspend everything in the oil.

Neglected Engines

This can lead to these pieces or particles blocking or partially blocking things they shouldn't. In general, the oil pump pickup can be susceptible though it is fairly large and it would take a lot of pieces/gunk to block it completely and stop oil flow. You would then get an oil warning light or the oil gauge would drop to zero and this requires you to shut down the engine immediately. If not, it will cause major damage.

Oil Filter in Bypass Mode

Once the oil is past the pickup and oil pump, modern engines have an oil filter to clean the oil before it goes into the engine. The majority of these filters have a bypass valve. This is there for when the filter becomes clogged with use and won't let oil up into the engine. The valve operates and then passes dirty oil through the engine without it being filtered. While not good for the engine long term, it keeps it running.

If the oil filter is in this state due to neglect and you use an oil flush, it will let more dirt into the engine which could cause partial or full blockages. You often see this on forums where an oil flush is used and it can create a new issue. It is not a direct cause of the oil flush, it is the filter being in bypass mode.

Playing It Safe

You could buy a cheap oil filter and change it for the old one before using the engine oil flush. Once you use the oil flush, throw away the cheap filter and replace it with a new one and add fresh engine oil. You should only need to do this on the first oil change.

The other thing to check is the engine oil. If it is far thicker (like treacle) than the new oil it may pay to also drain the old oil and replace it with a cheap oil. With the cheap oil and filter on board then use the engine oil flush. Once done, replace both with a new oil and filter. Again, you only need to do this on the first oil change.

High Mileage Engines

High mileage engines are already worn and the gunk and gum can sometimes help stop seals leaking or at least slow up the leak so it is not obvious. Engine oil flushes remove this so the leak can unfortunately become worse. It gives the impression that the oil flush caused the seal to fail which is not the case. The seal was already on the way out, the oil flush just made it more noticeable.

There is really no work around except to replace the leaking seal. Depending where it is on the engine this can be expensive. The price of the seal itself is cheap compared to the labour involved to replace it.

A good rule of thumb is check around the engine before adding the engine oil flush. If you have a seal that is weeping or dripping engine oil then putting an oil flush through the engine will not help it. Simply change the oil and oil filter or replace the seal.

Engine Oil Flush Summary

This guide is to help you understand why and when you need to use an engine oil flush. For most engines an oil flush is OK to use. It is only if an engine has been neglected, is high mileage or both that more care is required. Each engine will be different and knowing how bad it is internally is hard to tell from the outside. If in doubt seek advice from a professional mechanic before doing anything to it.