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If a little sealant is good, then a lot must be better....I have always been surprised at how many different ways people can come up with when trying to seal engine or drive train parts and, I might add, result in varying degrees of success. If your level of success in properly sealing components together is any less than 100%, then this article is for you. 


Years ago, a mechanic had to make his own gaskets from the limited bulk stock available. The choices available were different thicknesses of paper and cork which by themselves certainly didn't create a good seal. So, the mechanics had to come up with additional liquid coatings for any level of success.

A small oil or coolant leak, at that time, was considered normal and acceptable.

Today's high tech components require gasket sealing technology with an exacting science because no leak is the only thing that's acceptable. 

Then, a mechanic gets hold of the job, doesn't prep the surfaces correctly and slathers on a pile of goop totally eliminating the design features of the gaskets and then, hopes he's created a good seal.


Well, there may be a few reasons.

 - Maybe he just doesn't know any better because he was never trained properly.

 - Probably, the people who were supposed to train him didn't know any better themselves.

 - Maybe he's using (or have been given) cheap, inferior gaskets that can't do the job without having to use drastic measures

 - Or, maybe he's just trying to cut corners in order to make a buck.

Whatever the reasons are, it doesn't work.

I see customers returning again and again complaining about the same leaks that the shop just simply can't seal properly which forces the customer to find another shop to do the job.

This leaves a bad taste in everybody's mouth.  

It has to be done right, the first time.

Here are a few tips that will help to insure a perfect seal all the time.

Cause and Affect

You have found the source of the leak and are ready to report your findings. But, before you do, can you tell what caused the leak in the first place?

If it was because of age and deterioration, you will probably be okay. But, if something else caused it, the repair job will never be successful.

Here are just a few things I have found to cause reoccurring leaks;

RWD Pinion Seal; contaminated fluid, plugged vent, worn or seized shock absorbers, worn pinion bearings, damaged yoke, bad u-joints

RWD Transmission Output Seal; worn or damaged drive shaft support bushing in rear housing, worn or seized slip yoke, bad u-joints, out of balanced drive shaft, worn or broken transmission mount, drive shaft too long or too short (from raised or lowered suspension)

Crankshaft Seals front and rear; excessive crank end play from worn or damaged main thrust bearing, plugged PCV system, worn or damaged harmonic balancer

These are just a few external defects that can cause the failure of seals and gaskets. The point to remember here is that you have to ask the question "What caused the leak in the first place" and check for any probable causes before you commit to the reseal job.

Knowing What's Ahead of You

The first and most important of any reseal job is to know what's ahead of you. If you have done this particular job before, you are well aware of the potential pitfalls and warnings. If not, find the repair instructions and read them.

You will find that you may require special tooling or that other parts will have to be removed and possibly discarded to access the part you are trying to seal that you haven't thought of. Also, you will become aware of any special installation instructions, warnings and specific torque specifications.

For example: Because of the light construction of some engine blocks, proper torque specifications and sequences have to be applied when installing an intake manifold. Otherwise, the block could twist and cause main bearing failure.

Since we're talking about assembly instructions, one area that has been the topic of many discussions is cylinder head bolts;

  • should they be replaced or not? 
  • what's the difference of 'torque angle' versus 'torque to yield'?

See "Torque Angle Versus Torque to Yield" for more. 

Prepping the parts

Clean, clean, clean. I can't stress this enough.

How clean? Well to give you an idea, even the oil from a finger print can be enough to contaminate the surface and cause a leak.

Here's why;

The dry, contact surfaces of both the gasket and the surface is your first line of defense against any leak. If any small film of oil or glycol is on the surface when the gasket is applied it will be trapped under the gasket when it is tightened. As soon as thin, hot oil hits that area, it will creep under the gasket because a path is already there for it to follow.

Important Note;

Do not reuse old gaskets. Once they have been compressed, they cannot compress a second time. Plus, since they have conformed to the old surface, you will never get them reinstalled in precisely the same position.

Rubber seals, on the other hand, can be reused if they are 'young'. We'll talk about rubber seals and gaskets later.

Getting all the old gaskets off sometimes is a problem in itself but regardless, the old gaskets have to be totally removed. There are many different methods to do this but some you have to be real careful with.

Gasket Scrapers

These come in different widths and lengths but a gasket scraper is only as good as its blade. If you can achieve a straight, single beveled, extremely sharp edge to your scraper, removing stubborn gaskets will be quick and painless. A good tip would be to find a sheath to put it, or them, in to protect the edge while it's bouncing around in the tool drawer.

Plus, you are not limited to the gasket scrapers available on the tool truck. 

Be imaginative.

Old flat bladed screwdrivers can be heated, bent and sharpened so you can get in to those narrow corridors or odd angles to be cleaned. 

Razor Blades

Razor blades are fine but don't use them without a proper holder to avoid cutting yourself. Most use blades in place of a regular scraper so they can get an instant sharp edge but I, personally, don't like them because they tend to break too easily under heavy pressure. I use them for cleaning glass.

Air Scrapers  

These are designed similar to air hammers or chisels but they are smaller and have a much lighter, higher frequency hammer to them. They are great for saving time and getting under those stubborn, baked on gaskets especially when you're dealing with large surfaces. A kit comes with different blades for different jobs but you have to be really, really, careful, especially with soft surfaces like aluminum because it is still an air chisel.

Abrasive Pads

These pads, most commonly, the 3M Scotch Pads, attach to a pad holder that you would use in a high speed, die-grinder. They come in different abrasive grades which makes really short work of gasket removal. It is the tool of choice for a lot of technicians because it is so quick and effortless but there are big WARNINGS that go along with using them.

The first is that the abrasives that are embedded in the pads will come out as it wears. These abrasive particles are extremely hard and very small and if they get into the oiling system, they will damage gears and bearings fairly quickly. Because of this warning some shops have selected not to use them at all. Myself, I still use them but very selectively; parts on the bench that will be washed and dried afterwards as well as cooling system work.

The second warning to heed is that these abrasive discs are so aggressive; they will grind down aluminum and other soft metals very easily.

One slip and you could be buying another part.

So, be very gentle with the pressure you apply. Even better still, don't use a fresh pad if you are going to use them on soft metals.

There are other abrasive discs that are less aggressive. These look like round plastic brushes. They too, come in different grades of abrasiveness. They say the advantages here are that as it wears, the pieces that come off are large enough for an oil filter to capture so it is less likely to damage vital components (That's still not 100% in my books) and they are less aggressive which means they are better suited for use on soft metals.

Chemical Gasket Removers

These, I have tried but have had very little success with. Plus, I was very concerned about what would happen when these chemicals mix with other fluids. (It's probably not a good thing.)

So, choose your gasket removing weapons carefully but remember; all gasket material has to be removed.

Note: One of the reasons to remove all signs of old sealants would be in case of possible incompatibility with new sealants. I found this out quite by accident.

I was using GM's sealant called GMS and ran out. To finish the job I used a regular RTV sealant and to my surprise it started to smoke. Apparently the two different chemicals were not compatible with each other and started to react, giving off a lot of heat and smoke. So, the point here to remember is that different companies produce different products with different chemical makeups.  Don't mix them.

Don't forget the bolts and bolt holes.

All mating threads of bolts and holes have to be clean and in good shape in order to get a proper and, even more importantly, even clamping force on the gasket. For example; if a blind hole has old sealant in it, the bolt could bottom out first before you get enough compression on the gasket. Also, having old sealant, thread locking compound or rust will cause the threads to bind while tightening giving a ‘false' torque reading or even worse, the bolt could break before the gasket is fully compressed and secured.

If there's evidence of thread sealants or locking compounds, run a tap down the holes and blow out the loosened debris.

Now that you have removed all the old gaskets and sealants, you have to clean and dry the mating surfaces properly. For the loose pieces, solvent parts washers are most commonly used and are very effective only if the solvent is fairly fresh. Old, dirty solvent won't clean anything. But, you are not finished yet. After the solvent has lifted the oils and greases, you have to remove the solvent because that layer of petroleum will prevent a good seal. To do this, the garden hose works very well. The pressure will lift the solvent and, after blow drying, you have a perfectly clean and dry surface.

Even better still, automatic hot parts washers are the ultimate for those who can afford the investment and space. They clean beautifully, even getting into those places that a brush and solvent can't reach. Plus, they are a serious time saver.

For on-vehicle cleaning, use ‘brake clean' and a clean rag to finish preparing the surfaces. You can also use alcohol or other similar products that will remove any petroleum or antifreeze films and will evaporate without leaving a film.

Gaskets and Seals

There are good qualities and not so good qualities. Just because it has a brand name on it, doesn't mean it is built with quality materials. The junk gaskets are still out there but, it seems, very few shops or techs know the difference and, worst of all, nobody complains. As far as the distributors and manufacturers are concerned, if you keep buying them and not complain, that means the product is okay and nothing will change.

(Note; Here at ASBN, you can bitch and complain about these poor quality products you are paying good money for and expect to trust them. We will post and forward these to the manufacturer. We will be heard!)

There is a big difference in the performance between quality and cheap gaskets but ironically there isn't a big enough difference in the price.

Check it out yourself. You will find, like I did, that the difference in price is mostly because of missing parts. If you buy the extra parts to create a complete set, the price is now pretty close to the higher priced sets.

How can you tell the cheap gaskets and seals from the good ones?

Well, in most cases, it's quite obvious.


Head gaskets and intake gaskets appear to be stamped out of bulk stock with rough or even cracked edges

Seals are single lip instead of the original double lip design

Rubber formed gaskets are hard, have a poor fit, do not have the raised webbing on the contact surface

Gasket sets are incomplete. Vital gaskets or seals missing to complete the job.

No parts list or model fit application listed on the package forcing you to open the package to see if everything is there and if it is not, you can't return it because you have opened it.

No special instructions, warnings or recommendations for use with their products.


Contents of package and application fit listed on outside of package

Gasket sets are complete for that job

If they recommend sealants, they come supplied

All gaskets have a ‘finished' appearance

Gasket materials are different for each component that requires special attention

Special installation instructions and warnings are included

The other way of telling a quality product from its cheap counterpart is in its performance. The problem here is that if the job comes back for warranty because it's still leaking, it is most likely the mechanic's poor installation job that will get blamed for it.

Here's an example; I replaced a difficult water pump only to find it leaking after an hour of running. What caused it was the gasket. This was not gasket material with sealing qualities. It was an absorbent and dissolving piece of cardboard that came with the water pump that originally appeared to be proper gasket material. The rep couldn't believe it until he saw it. Here's a situation that even the pump manufacturer was trusting the gasket supplier and would never have known if I didn't take the effort to let them know and be able to prove it.

Now, You're Ready to Assemble

 Here's where many mechanics will start to think about coating the gaskets with sealant because they feel the plain gasket may not be good enough. But, if both surfaces are flat, clean and dry, a quality gasket is all you need. If it is a rubber gasket, a dry surface is absolutely necessary. You can't get any better than a rubber seal against a clean, dry metal surface. Adding a sealant will also be adding a lubricant which will allow the gasket to slide out of position during tightening. The dry contact surface will keep the gasket in place creating an impenetrable pressure seal.

If there are sharp corners or an uneven surfaces where two parts are joined, gaskets and rubber seals will not be able to conform, so use a very small amount of RTV sealant just in the corners or joints.

There are other areas sealants will be used instead of gaskets or with gaskets. But you will also see that these components were designed for sealants and not gaskets. The key here is to read and follow the assembly instructions and you won't go wrong.

There are times that the additional use of sealants does come in handy. For example;

Engine oil pans

Most early models and some newer, require that the pan gaskets be installed on the block before the pan is installed. This is fine when the block is on an engine stand, upside down, but quite tricky when it's in the vehicle, especially if the gaskets include rubber end seals along with cork rail gaskets. What I do is first insure that all surfaces are perfectly dry and clean. Then, I use a spray gasket compound like Permatexâ High Tack Spray Gasket. I spray the block rails along with the corresponding contact surface of the gaskets and let them dry for about 15-20 minutes. When they are dry to the touch, I carefully position the rail gaskets into position working from one end to the other. (Yes, this is the same procedure you would use with contact cement when applying counter top laminates for your kitchen.) Once these gaskets are permanently glued into position, I can then add a small dab of silicone sealer in the sharp corners of the rear main cap and front timing cover and then install the front and rear end seals. The pan is now installed dry.

This method works very well because it allows you plenty of time to get the pan in position without having to worry about the gaskets especially if it's a Ford where you have to re-attach the oil pump pick up tube during assembly.

I also use this method of “gluing” a gasket onto a component where I find that it will be difficult to keep a gasket positioned during assembly like water pumps and some valve cover gaskets. Don't forget to let the glue dry first otherwise it will not stick and it will act as a lubricant which will allow the gasket to ‘slide' out of position during tightening.

I hope these tips are helpful in building your confidence in gasket sealing and eliminating any comebacks.

The additional time it takes to be a little more picky and methodical is a heck of a lot cheaper than having to do the job over again.

Bob Paff

ASE Master Technician

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