Bypass oil filters unnecessary with regular oil change

Hey there, time traveller!
This article was published 03/01/2003 (8309 days ago), so information in it may no longer be current.

QUESTION — Have you seen the engine bypass oil filters that are so popular Down Under and what do you think of them? They all claim to pay for themselves with increased engine life and fewer oil and filter changes, but what is the real life scenario? I think it sounds good, but could it be too good to be true? Also, I don’t think that $200 is worth spending on something that “might” work. Your opinion would be appreciated.

ANSWER — Bypass oil filters were used on automobiles long before the current full flow type filters became common. All engine oil passes through a full flow filter before it goes to the rotating engine parts, so this type of filter is the best if only one filter is used. Bypass filters filter only some of the oil before returning it to the pan, so dirty oil could still get to moving engine parts. Using both types of filters would be the best method, although there is the extra cost and complexity.

Some large trucks use both filtering systems, and I remember Ford using it on a small four-cylinder diesel light truck engine. The Ford bypass filter also contained a chemical additive package to help maintain the oil.

Is it worth the cost of adding a bypass filter system? Better road conditions, better engine materials, and better oils have extended engine life on most automobiles to as long as the rest of the vehicle will last. Adding another filter system will clean the oil better, but wear problems in engines are uncommon lately if regular oil and filter changes are performed. It is usually chemical (acids) contamination of the oil that can damage engine parts and another filter will not remove the acids. Only oil changes will do that.

QUESTION — I had a head gasket replaced on my 1994 Grand Am Quad 4. It was fine for about a week. Then I noticed after the engine cooled it would leak about an ounce of coolant on the driveway. The leak is at the back of the engine. The coolant level doesn’t seem to go down appreciably but I am concerned. The car is running fine. I tried the GM tabs but they didn’t seem to work. It almost seems to be an improper torquing of the head bolts. Can they be retorqued? The head was machined and had no cracks. Your comments would be appreciated.

ANSWER — I would say it is time to take your car back to the repair shop. The leak may be coming from the head gasket, but the water pump is also located on the firewall side of this engine and it or one of the hoses may be leaking. The first step is to identify where the leak is coming from.

A visual inspection can sometimes locate the leak, but because the leak is small and intermittent, the repair shop may need to use a dye. A special fluorescent dye is added to the coolant and a black light shone on the suspected areas. The leak will show up as a brilliant green colour.

If the problem is the head gasket/cylinder head area, the head gasket should be replaced again and the machined surfaces inspected for warpage. The cylinder head has already been machined, but improper torque or overheating can warp it again. The engine block should also be checked, although the top of the block (called the deck) usually doesn’t warp.

The torque sequence for the head bolts on this engine are critical. The bolts are tightened in two stages: to a specified torque and then turned an additional number of degrees. The bolts are a torque-to-yield type that stretch to the elastic point when torqued and do not need to be retorqued. If a bolt is loose, it should be compared to a new one to make sure it is not stretched. Replace stretched head bolts, although they can be reused on this engine if they are in good shape.

The GM tabs you refer to are sealant tablets that GM recommends using whenever an engine has had major work done. They will seal small areas that could seep coolant, but are not designed to seal larger leaks. I would not recommend using other cooling system leak stopping chemicals, because these can plug small passages in the heater core.

Jim Kerr is an experienced mechanic, instructor of automotive technology and freelance journalist. You can e-mail questions to Jim at the address below.

kerr.jim@sk.sympatico.ca