Level checks – heed the Max

Posted on August 14th, 2017 by Rob Marshall


While ensuring correct fluid levels is vital for year-round reliability, a useful reminder to help prevent a ruined summer holiday is to make sure that your car is in good health, prior to venturing on a long journey. Yet, while levels should not be permitted to fall below any ‘minimum’ marks, it is essential to remember that adding too much can have negative repercussions, too.

Engine Oil

Prolonged, high speed motorway trips place particular strains on engine oil, which can run at temperatures higher than the cooling system, often well over 100 degrees Celsius on a hot day. With most cars lacking an oil temperature gauge, low oil levels can make the exiting lubricant run hotter, potentially reducing its effectiveness to protect the engine from seizure.

Every engine consumes oil, to some extent. A falling oil level may not mean necessarily that an engine is worn-out. While allowing the level to fall below the minimum mark increases the risk of engine damage, so too can filling it to the maximum and beyond (see picture, the level of which is just over the maximum mark). Many diesel engines, for example, are designed to contaminate their oil with fuel during certain running conditions and this causes the oil level to rise naturally. If you fill the engine oil to the maximum mark (or over), you reduce the engine’s capacity to tolerate the escalating oil level. An over-filled sump can not only cause the oil to pressurise and be forced-out of the engine but, in bad cases, with certain diesels, the oil can enter the engine’s inlet, causing the engine to run uncontrollably at maximum speed, until it either explodes, or seizes.

Check the vehicle’s handbook carefully and follow its oil level checking advice, because instructions vary.


Any sudden drop in the engine anti-freeze level must be investigated. Yet, the coolant level must be checked with the engine cold and the car standing on a level surface. As water expands, when hot, checking the level even with the engine warm will give you an unreliable reading. Checking a cold level also prevents the risk of burns, caused by steam escaping, as you unscrew the cap.

Over-filling the coolant bottle is not as serious as overfilling the engine oil but excess water, at close to boiling point, can be forced-out of the cooling system, when the engine is running. This can spray over the engine bay, not only causing unsightly staining but also a break-down, should the electrics become soaked.

Brake / clutch fluid

Brake fluid levels fall gradually as the brake linings wear but sudden drops should be noted. Overfilling the brake fluid container can cause fluid to leak out, which is not good for your car, because it is a most effective paint stripper. Brake fluid’s moisture-absorbing characteristic also can promote corrosion. The hygroscopic nature also means that the fluid should be renewed every other year.