Oil Pressure & the Spin-On Adapter

Reprinted from The Vintage Triumph, Number 49

Sudden oil pressure loss in your TR6 or TR250 may not be cause for total panic. If the car is equipped with a spin-on filter kit the problem might only be that the incorrect filter has been installed. Full flow oil filtration systems such as used by Triumph pass all of the oil from the pump through the filter before proceeding to the bearings. Any stoppage at the filter results in no oil pressure at the bearings. The original canister type filter employed a filter reilef valve inside the canister. This device ensures that in the event of a plugged filter, oil is allowed to bypass the filter. Unfiltered oil is preferable to none at all!

Filter stoppage may be from contamination or simply because the oil was too cold and thick to pass through the filter medium. In my case, 20W50 oil at 20 degrees dropped my pressure from 70 PSI to 20 PSI. As the engine warmed the pressure rose, but not fast enough to calm my nerves. Quickly checking the logical problem areas gave no clue, the plugs had not been forced from the end of the rocker shaft. Also the pin securing the gear to the oil pump drive shaft appeared intact. Removal of the large hex pressure regulating valve from the side of the block showed the spring in fine condition. With it removed a brief start of the engine produced a large puddle and confirmation that the oil pump appeared functional.

Studying the shop manuals lubrication flow chart led me to believe I had a restricted filter. Consulting a FRAM filter catalog, I then discovered that the recommended filter, a PH 2825, did not seem to be equipped with a filter relief valve. Further research suggested that a PH3600 filter was a perfect phyical match, and most importantly, it was equipped with a 9-12 pound filter relief valve built in. This filter was fitted to 81-92 Ford Escorts and 86-95 Ford Tauruses, making it readily available for a long time to come.

Ever the optimist, I screwed on my newly purchased PH3600 filter, and poured in some 20W oil. After pulling the coil wire, I spun it over for a minute, replaced the wire, and twisted the key. Instantly, 70 pounds of oil pressure! In one busy afternoon I had solved a mystery and learned a little about oil filters. More importantly, I had not spent a lot of money an an unneeded engine overhaul.

Triumph engineers designed the TR6 oiling system with the filter relief valve. My experience has shown it to be needed for the system to function correctly. The spin-on adapter is staying on my TR6 but the choice for a filter is now the PH3600 or an equivalent.

Editor’s Note: If you would prefer to use a different brand of filter, other brands have functional equivalents: Motorcraft FL-400A, AC X21+, Purolator PER195, WIX 51516. Regardless of which of these you choose, I am convinced that this model of filter is the best match for the TR6 spin-on adapter, because of the built-in filter relief valve and relatively high surface area, allowing for higher oil flow than a smaller filter.