Penetrating oil: WD-40, Caramba & Co. in the test
Multi-oils, also known as penetrating oils, promise a lot: they should lubricate, dissolve rust and at the same time protect against it, clean metals, displace water, maintain contacts and creep into every little crack in order to perform all these miracles there. No wonder they have a permanent place in almost every household, in every workshop and in numerous spare wheel wells. AUTO BILD tested nine multi-oils.
Winner of the AUTO BILD multi-oil tests: Sonax SX90 Plus
By far the best lubricating effect, but only mediocre creeping ability, otherwise top performances everywhere. In the test, the Sonax SX90 Plus multi-oil achieved 162 out of 190 points and was rated “highly recommended”.
Price-performance winner: WD-40 multifunctional product
How AUTO BILD and KÜS tested
AUTO BILD tested the multi-oils together with the automotive expert organization KÜS in a specialist chemical laboratory. The main property of oil is its lubricity. The lubricity of oils and greases can be scientifically tested with a four-ball apparatus and a friction wear scale. In the four-ball test, four test balls made of steel, such as those found in ball bearings, run in an apparatus, with three balls being clamped in a pot. This is filled with eight milliliters of the oil to be tested. The fourth ball, which acts on the bottom three from above, is connected to the drive and rotates at 1500 rpm for 60 seconds with an adjustable test force.
A distinction is made between go and weld forces. Good power means: lubrication is guaranteed, the balls rotate. Welding power: no lubrication, the balls weld together. The higher the test force with the lubrication still present, the better the oil. During the transition from the good to the welding force, the test bench begins to vibrate and the contents evaporate. As soon as this occurs, we record the readings.
The fretting test is also about the lubricating properties: Here, material abrasion of a cylinder made of hardened steel is measured on a test bench under an electron microscope. The smaller the rubbed area, the better the lubricating effect. To test how well the oils protect against rust, we exposed unpainted, sprayed and dried test panels to five percent salt water vapor for 60 hours. Since multi-oils often come into contact with plastic, good material compatibility is also important here. For this purpose, polycarbonate test surfaces were sprayed with the respective products and heated at 80 degrees Celsius for 48 hours. Stress cracks then allow conclusions to be drawn about the quality of the oils.
Water causes rust and contact problems in electrical systems. Gray cast iron chips are used to test how well the oils displace water. 40 grams of these chips are mixed with five milliliters of tap water and then shaken. We then spray from the respective can onto the gray cast iron/water mixture in a test tube for five seconds. Water and oil collect in the special test tube that narrows towards the bottom – water at the bottom, oil at the top. The more water collects, the higher the water displacement. In order to make the oil’s creeping ability visible, a grid was placed under two glass plates lying one on top of the other. We then let 20 microliters of multi-oil crawl for two minutes. The larger the visible oil film area, the better it creeps. We could not determine any differences in the rust-dissolving effect of any of the oils, so no points were awarded here.
The test results at a glance
Let’s make it short: Of the nine tested multi-oils, only one is convincing across the board, Sonax SX90 best keeps the promises made on the can label. In terms of its lubricating effect in particular, the spray from Sonax can show measured values that none of the tested competitors achieved. For this purpose, the maximum test force is determined in the four-ball apparatus, at which the balls located in the oil are still running without welding together. With the Sonax SX90 this only happens at 2000 Newtons; this corresponds to a load of 200 kilos. The second best, Nigrin, welded at 1600 Newtons – a big difference, but also a good value in this test field, because the lubricating effect decreases rapidly from the second place. In general, Nigrin is hot on the heels of the all-rounder from Sonax. It is correct in all test criteria perfomance, only the rust protection leaves a lot to be desired: After 60 hours in five percent salt water vapor, three untreated test panels sprayed with the product have already started to show a thin layer of rust. Pity!
From fifth place onwards: none of the multi-oils are multifunctional anymore! With a total score of 98, there are three products in fifth place. Caramba lubricates and protects mediocrely, but it attacks plastic. There are deep cracks in the polycarbonate test strip. Liqui Moly is in the middle when it comes to rust protection and lubricity, but gives away points when it comes to the function of the spray can: no universal spray head, no overhead spray function. The supplier Würth, which is aimed at commercial customers, achieved the worst lubricating effect next to the last-placed cheap oil from Bauhaus. In figures: Würth already welds at 1000 Newtons in the four-ball test, Bauhaus at 1100 Newtons. These are the worst values of all tested products.
With 1200 Newton, the classic from Ballistol almost reaches the WD40 level in terms of lubricating effect, but offers poor rust protection, hardly creeps and also does not displace any water. We could not determine any difference in the multi-oils in one test point: when testing the rust-dissolving properties. All screws stored in a salt bath could be loosened with a very similar torque after spraying. There were therefore no points in this discipline.
Conclusion on the multi-oil test
What a disappointing result: only two of the nine multi-oils tested achieve very good lubricating performance! The Sonax SX90 only allows itself a weakness when it comes to crawling ability, but convinces in all other criteria. Nigrin slips up on the rust protection. WD-40 and Weicon lubricate far less well, but protect very well against the formation of new rust. Particularly disappointing: the performance of the multi-oil classics from Ballistol and Caramba.