Engine & Exhaust / Q&A

Ask Away! with Jeff Smith: What’s a Good Way to Clean Engine Internals Without a Complete Teardown?

I have an older small block 350 Chevy pulled out of a 1990 Chevy pickup that ran before we yanked it out. I plan on using it in a 1950 Chevy pickup conversion I’m building. Since this is budget deal (aren’t they all?), I don’t want to rebuild the engine but I would like to make it nice on the inside. I could use some help with removing a lot of sludge and stuff from inside the engine. When I removed the oil cooler adapter, it was full of sludge and gunk so I’m assuming the rest of the engine looks that bad on the inside. What would be a good way to clean the engine internally without taking it apart?


We’ll offer some suggestions on ways to clean the engine on the inside, but as with most “mechanic-in-a-can” remedies, the solution may not necessarily do the job to your satisfaction.

Since the engine is already out, we would recommend spending a little extra money for an engine gasket set and at least remove the intake manifold, valve covers, oil pan, and timing chain cover. Replacing all of these gaskets and seals offers a wonderful opportunity to reduce oil leaks once the engine is dropped into your cool ’50 Chevy pickup project.

As a 1990 engine, this is a one-piece rear main seal engine and it also uses a one-piece style pan gasket. But besides replacing the gaskets, this also offers you a perfect opportunity to clean the oil pan, valve covers, and the lifter valley of sludge that may have accumulated in these areas. Oil pans are famous for collecting thick gunk at the bottom of the pan. Cleaners may eventually remove most of this but that may only work if the accumulation is light. Heavier sludge buildups will require physical removal.

Now that we’ve offered our recommendation, there are ways to clean the inside of the engine. The classic old school technique was to drain the original oil and remove the filter. Add some cheap engine oil with high detergents but substitute a quart of automatic transmission fluid (ATF) and run the engine with this for about 20 to 30 miles of basic driving and then drain the oil, remove the filter and add fresh oil and a new quality filter.

When we asked oil tribologist Lake Speed, Jr. for his opinion, we were surprised to discover that he does not recommend this technique. He says that ATF does not use the same high levels of detergents used in engine oil and as such should not be used in an engine . He says that he knows many enthusiasts have used this technique, but he does not recommend it.

Another common technique is to substitute diesel engine oil in place of regular gasoline engine oil because diesel oil generally has much higher detergent levels. Speed, Jr. has a wealth of experience with high performance lubricants and he suggests that a diesel engine oil would be a much better approach. An example of this would be diesel oil that contains much higher levels of calcium, which is a very popular detergent additive.

According to Speed, the key is a balance of low zinc and phosphorous with a high level of detergents like calcium. Diesel oil, like gasoline engine oil has undergone some substantial changes in the past few years and current zinc and phosphorous levels are much lower level and more or less even with SN engine oils for gasoline engines.

Speed, Jr. suggested using Chevron Delo 400 LE which has lower levels of zinc and phosphorous while maintaining decent levels of detergents that will help clean the engine more efficiently.

Other additives that in the past have also worked include Seafoam internal engine cleaner or Marvel Mystery Oil. In each of these cases, we would add a quart of this additive to complete a normal engine oil change, run the engine for roughly 30 minutes to get the engine up to full operating temperature and then drain the oil and replace the filter. These processes may need to be repeated more than once and our estimate would be that the only way to know for sure if the engine is cleaner is to first remove at least one valve cover to establish a baseline for cleanliness. Perform the cleaning session(s) and then again pull the valve cover to check for progress.

Frankly, I don’t think that these steps will be nearly as successful as taking the engine apart and cleaning (at least) the oil pan and valve covers the old fashioned way with solvent and a brush.

Once you’ve completed the sludge cleaning another suggestion would be to use a high mileage oil in the engine instead of a typical SN oil. There are several viscosities and brands to choose from. We found a couple of choices from Pennzoil and Mobil 1 that offer mineral-based oil as opposed to the more expensive synthetics that offer higher detergent levels also with other additives that can be helpful especially if you do not change all the gaskets and seals in the engine.

Internal Engine Cleaning Parts List

This is an oil pan from a small block Chevy with 180,000 miles that we recently disassembled. The bottom of the pan has about 1/8 inch of nasty, black sludge that would be difficult to clean just by changing oil. Doing the job right means removing the pan to get it clean. (Image/Jeff Smith)

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  1. I read many years ago – likely in Hot Rod and/or Car Craft magazines that the “grit” in ATF destroys coated piston rings and wipes out bearings. The only time ATF should touch the inside of an engine is the first wipe down of the freshly-bored cylinders after getting your block back from the machine shop; ATF, dissolved powdered laundry detergent, 50/50 Super Clean, WD-40, non-detergent 30 weight, in that order. This was from likely over 30 years ago; maybe current Dexron III (IV?) doesn’t have the “grit” any more…

    • Dana
      I’m unclear as to your definition of the term “grit”. That usage implies some kind of abrasive. There are no abrasives in ATF but there are high levels of detergents. With dirty hands, wash your hands with ATF and they will come clean because of teh detergents. As mentioned in the story, our source Lake Speed, Jr. is a tribologist – an oil expert does not recommend ATF for use in engines which is why we made the point. I seriously doubt that this “grit” information ever apeared in Hot Rod or Car Craft because it is untrue. If it did appear – it would have been an aggregeous error on their part which is why I doubt that is the case. I am confident in this because I was editor of both magazines during the 1980s and ’90s.

  2. The other “cleaning process” is getting the carbon out of the combustion chambers and piston tops/rings. GM used to sell a “top end cleaner” that you poured into a warm cylinder thru the spark plug hole to soak the cylinders/rings. I can’t find it anymore. I think BG sells a pro-only top end cleaning system that uses some kind of solvent to clean the chambers as you run the engine.
    This cleaning process is needed because a bunch of the Gen IV LS engines had a cylinder/ring carbon problem when the DoD solenoid activated and fogged the crankcase with oil mist. This would coke up the rings and cause oil usage and plug fouling. E39/E46 BMW 6 cylinder engines are also bad about chamber and ring coking. I’ve also heard of walnut shell ingestion and many other solvents – none of which sound really great for catalytic convertor life.
    Curious what others have tried…

  3. Fishook Kennie says:

    I am 76 years young and have been working on cars and motorcycles for most of my life both as a hobby and professionally and ofcourse with guidence of both Hot Rod mag and CarCraft.I also was a journyman automotive Machinist for years. I worked at an engine rebuilder late 60s through the late 70s. As an apprentice you had start in the engine tear down room. To tear down,clean and prep engines to out to the machine shop to be machined, re cleaned then assembled. You would not believe the crap I found in engines. As for sludge well, the oils back then just were not as good as they are now days. I always preferred Valvoline Racing oil or Mobile Racing oil back then. Back then I also raced Super Modifieds and we used Kendal Racing oil in those engines. I have tried just about every enternal short cut engine cleaner you can imagine over the years. There just is no substitute for for regasket and resealing of a used engine. This gives you the opportunity to thoroughly clean the engine and while your at clean of replace the oil pick up screen and check a main or two and a rod or two before commiting to the engine as is. Looking at the bearing, cylinder and piston skirt color and wear patterns can be a money and time saver in the long run.
    Thank you guys for what you do.
    Fishook Kennie

  4. Harold Lovett says:

    When I disassemble an engine just to rebuild or rering, I clean it with Oven Cleaner. Removes all of the sludge and grease and old paint.

  5. Steve Knight says:

    After reassembly, get a 6-pack of the best oil filters you can find, and a few gallons of oil. Start it up, warm it up, change the oil and filter. Rinse, repeat. Could cut the oil filters up and look at them, although the act of doing that frequently deposits more crud. be careful. On the other hand, watch a few episodes of Roadkill…and you will realize you are doing fine.

  6. I bought my 1986 Camaro in 1992,third owner, the lifter valley needed the use of a screwdriver and chisel to remove the solidified mess that was in there, it was also around the valve springs.
    All the service receipts I had did not show an oil change just petty warranty items.
    I reckon I was the first to do an oil change.

  7. JOHN HODGE says:

    Hi Jeff! this concerns my 1976 EL CAMINO SS. it has the 400 small block. back around 1985 i had the motor rebuilt w cam, flat top pistons, 350 connecting rods etc. i put on a set of mildly ported L-82 Corvette heads. are these heads any good? it sat for a few years and i’ve got it back out now that i have the time. doing some upgrades. it has a torker 2 w holley 750 vacuum sec. i was thinking of a new set of aluminum heads thanks! John Hodge ps I’ve owned it since 1977!

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