Mysterious Small Block Chevy Oil Leak
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Do you have a small block Chevy V8 in your car or truck? Does it have oil all over the engine compartment with no obvious cause for a leak? Then this tech article could be for you. I heard about this one in a car magazine, and it turned out to be the cure to a problem I was having - the scanned picture below is from that article.

On the front of the block on the passengers side, near the fuel pump mount there is a small mounting pad with a machined hole in it. This hole was originally used for front mounted engine mounts in the '50s and in later years various types of accessory brackets have used this hole as well. In many applications it is not used and the hole is often left open after the engine has had any major work done on it such as a rebuild. The problem is that this hole is drilled through to the fuel pump pushrod cavity, and if not plugged it is a non-obvious but very much open path from the internals of the engine to the outside world. Under higher RPM conditions or "spirited" driving, this hole can do various things from simply seep oil, to outright spray oil, or simply just emit a fine oil mist that will get blown all over your engine compartment and turn it into a gross mess in a few thousand miles.

The fix is to get a short 3/8-16 bolt that is short enough to not contact the fuel pump pushrod, coat it with sealant, and install it into the indicated hole. Problem solved. If you already have something bolted to that hole, make sure you have sealant on the bolt you used so it won't seep oil around the threads.

MysteriousSmallBlockChevyOilLeak.jpg (155518 bytes)


In my case, the entire engine compartment of my 1975 GMC Suburban showed evidence of an oil leak after I rebuilt my engine. Virtually everything was lightly coated with oil and getting very grimy in short order. Occasionally I would get some oil smoke from under the hood as these oil bits hit the headers and burned off. In short, gross and not good. My nice new shiny rebuilt engine was looking like an oily mess after just a few thousand miles of driving and I wasn't happy. I was hunting all over the place and chasing various problems until I found this tech article, and it really helped clean up my engine compartment. It's going to take a while to get all the nasty oil film off everything, but at least it's not getting any oilier each time I drive the truck... I still have some other drips to take care of, but I believe this was the bulk of the problem I was having. Well, that and the leaky steering gearbox that drips power steering fluid all over the place. :-(

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Page last updated 01/02/2009 01:51:39 PM