I race a Volkswagen Golf 2 and noticed at a recent race at Zwartkops Raceway that my car’s oil pressure was in the region of 600 to 700 kPa at start-up and then dropped to about 100 kPa after a few laps as the engine started heating up. Apparently, the reason is that the oil got warmer and then became thinner, causing the drop in oil pressure.
As I find this excessive, can you tell me what the normal oil-pressure reading should be? I am currently using a 5W40 oil. Should I rather make use of a 10W40 (thicker) oil, or get the oil pump checked?
Secondly, when it comes to engine temperatures, can the engine be damaged if it runs at the 100-degree Celsius mark? My vehicle’s engine temperature went above 100 after a few laps (especially on the straights), and then dropped off noticeably when I braked for the corners. The engine builder removed the thermostat (it is known for causing trouble on these engines) and there was water in the system before and after the race.
Lastly, how much power is normally wasted in the drivetrain?
ZANE VAN ZYL, Randburg
Answer: Viscosity is the resistance against flow and shear. Water has a low viscosity and syrup has a high viscosity at room temperature, for example. The viscosity of single-grade oil (such as SAE 30) decreases with the increase in temperature. Multi-grade oils are designed to resist this tendency, but also have a low viscosity at low temperatures to aid lubrication at colder temperatures such as those that are experienced in colder climates during engine start-up (your 5W40 oil).
We spoke to a friend who races a Golf 2 in the Killarney GTI challenge and he says that the oil-pressure reading of his car’s engine is 700 kPa at the start of a race and around 600 kPa at the end of a race. His advice is to inspect the oil pump. He also runs 20W40 oil in his engine, which makes sense because a racecar’s engine-operating temperature is high and low-temperature performance is not a concern.
Regarding your second question: because the coolant system is pressurised, it can handle temperatures above 100 degrees Celsius without boiling, but we would recommend that you fit a larger radiator to improve the cooling capacity.
Lastly, power loss varies, but RWD vehicles experience bigger reductions. You can expect a loss of between 10 to 15% (sometimes even more) between the engine flywheel and the wheels on a FWD vehicle.