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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / July 2006Gasket Maker Question
I am replacing an O Ring on a Honda engine oil cooler and with Permatex Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the product states 24 hour cure. I assume I need to wait 24 hours, or will it acually seal faster?  Signatureramseybuckeye http://www.automotiveforums.com > I am replacing an O Ring on a Honda engine oil cooler and with Permatex > Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the > product states 24 hour cure. I assume I need to wait 24 hours, or will > it acually seal faster? > > -- When they say 24 hours for full-cure, that's what they mean. They made the product and silicone is still silicone. The cure rate has been about the same for years. However, I have found some that sets up very quickly and you could assemble in a few minutes and wait for the full cure. But when you block the air, you retard the curing. It is possible to have silicone that almost never cures, just like when it's in the tube. I have doubts as to whether this is a good application for the product anyway. If it had an O-ring, I would always replace it with an O-ring. If this doesn't leak right away on you, it certainly will degrade over time and leak-in my opinion. >I am replacing an O Ring on a Honda engine oil cooler and with Permatex >Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the >product states 24 hour cure. I assume I need to wait 24 hours, or will >it acually seal faster? What you are doing is quite dangerous. If a little string of silicone breaks off and blocks an oil metering hole it could be disasterous for the engine. Don www.donsautomotive.com The others are right about this not being a good way to go. Your real question is about the RTV. RTV cures when it is exposed to the moisture in the air. The cure time varies with the amount of moisture in the air. The instructions probably says 24 hours for "full" cure. The cure rate is exponential. That is it will reach 1/2 cure in a couple of hours 3/4 cure in about 8 hours and so on until full cure is achieved. In your application, I would roughen it up some with 220 grit and solvent clean the surface. Then apply a thin layer to each side making sure to keep it away from the oil passage. Since it needs moisture from the air to cure, wait 5-10 minutes before assembling. My experience is that RTV doesn't like hot oil under pressure. > >I am replacing an O Ring on a Honda engine oil cooler and with Permatex > >Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the [quoted text clipped - 7 lines] > Don > www.donsautomotive.com > The others are right about this not being a good way to go. > [quoted text clipped - 10 lines] > > My experience is that RTV doesn't like hot oil under pressure. I don't fully agree with your chemistry, but the facts are that if you dont do it correctly, you can get in trouble. If you do the work properly, and have the appropriate silicone compound, they work well. You ABSOLUTELY MUST let this material 'vulcanize' completely before putting it into service. This may take a number of hours. ( On the blue RTV, I found I got best results when letting it cure 12-24 hours. I got a lot of leaks until I developed patience in the curing process.) Some people on here used to recommend letting it wait a few minutes until it 'skins over', and then assembling it ready to use. NOT SO. It should stand undisturbed, dry, until the curing process is complete. As Don said, if you get an engine full of silicone strands or flakes, you have bought into trouble. > I don't fully agree with your chemistry, but the facts are that if you dont > do it > correctly, you can get in trouble. I guess I should have gone a little further, if I were going to say anything about curing. Common types are acetoxy/acetic acid/anhydride based, where moisture initiates the cure with release of small amounts of acetic acid. These are the cheaper and more ordinary variants. There are others, better and more expensive, which depend upon other reactions. A catalytic amount of moisture will start this type of crosslinking reaction. Too much water is not a good thing. And that is enough about chemistry. Read the instructions, err on the conservative side. Better still, use the O-ring that was designed for the application. > Read the instructions, err on the conservative side. Better still, > use the O-ring that was designed > for the application. Now...."there" is the proper answer! Ian > You ABSOLUTELY MUST let this material 'vulcanize' completely before > putting it into service. This may take a number of hours. ( On > the blue RTV, I found I got best results when letting it cure 12-24 > hours. I got a lot of leaks until I developed patience in the curing > process.) This is not possible in the environment that I work in. I've found, (and I've used it every day since GM first started using it) that the most important thing is that the surfaces are absolutely clean and dry. There can be no oil on the surfaces...etc. I don't notice any problems with jobs that I've done, and I often see the same cars back in my bay up to 5 years after I've performed a repair. Every now and then, the timing of the job happens to be right at the end of the day, and I'm able to leave the RTV untouched overnight after assembling. Pretty rare tho, and I've noticed no problems with quality when simply putting the components together and starting the engine right up. For you hobby mechanics, you have the time to let these things "set up". It's not possible for a flat rate dealer tech to do it this way unless I had 3 bays (which I don't). Ian > For you hobby mechanics, you have the time to let these things > "set up". It's not possible for a flat rate dealer tech to do it this way > unless I had 3 bays (which I don't). > > Ian I'm a diy-er, and I'll admit to not waiting for the silicone... once the parts are reinstalled, it's time to test-fire it. Not been a problem. of course, I'm not reinstalling an oil pan and immediately driving 500 miles... usually just around the block and then leaving it overnight, so I guess it has a chance to cure. My best/worst silicone jobs are the end seals on a "classic" SBC. Every third time we do it it leaks and I have to redo it. Always in the same spot, back by the oil sending unit. But I'm getting better. (don't ask why the intake is coming off so often... but if you wanna know, I've gone through a couple of engines... and swapped cams and intakes for more power... and the odd blowed up engine...) Ray > This is not possible in the environment that I work in. I've found, > (and I've used it every day since GM first started using it) that the [quoted text clipped - 14 lines] > > Ian The biggest problem I had was a dammittohell 84 Fiero with the crappola Iron Puke engine. We are talking about the coolant side, in this case. I tried ordinary gaskets in the set, and this damn thing leaked. I tried gasket sealer, and it leaked. And then I tried RTV Blue, and IT leaked, when used as you describe. I finally glued this POS together carefully and let it vulcanize overnight. Never another problem. Maybe this was a special situation, but it taught me a lesson in humility. > The biggest problem I had was a dammittohell 84 Fiero with the > crappola Iron Puke engine. [quoted text clipped - 6 lines] > Maybe this was a special situation, but it taught me a lesson in > humility. Ah...totally different situation. I "never" use RTV where coolant is involved. Maybe in a pinch, but I would also do what you did, it would have to cure for 24 hrs with no coolant, moisture, oil...etc, anywhere near it. GM tried RTV on water pumps and front timing covers on the early 2.8 v-6 engines, it didn't work. Ian > > Maybe this was a special situation, but it taught me a lesson in > > humility. [quoted text clipped - 6 lines] > > Ian Yep...They glued a lot of troublesome engines together with RTV in those days. I never had such a problem with the coolant system as I did with this car, where nothing appeared to work. The Blue RTV finally solved it. When I took that engine apart, it had suffered from several factory recalls and had Blue RTV everywhere. The block had cracked, and I had to rebuild an engine for it. We reengineered a number of spots on that installation, and -as far as I know - it never gave any problems again. And it had given MANY problems up to that point. Every factory recall seemed to have left the car in worse shape than when it was driven into the shop. > I am replacing an O Ring on a Honda engine oil cooler and with Permatex > Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the > product states 24 hour cure. I assume I need to wait 24 hours, or will > it acually seal faster? Most of the silicone adhesives sold for automotive application are moisture-cure silicones, so moisture in the air is the usual agent for curing and the rate of cure depends on the humidity. This can be accelerated with the direct application of water or steam. The problem is that if you get the outer skin to cure too fast that creates a moisture barrier that prevents the inner part from curing. That's more of a problem if the application is thick or pushed deep into a crack. A thin film of soapy water on the surface is considered by some to be the best method to get a rapid cure and a smooth blended surface (like when you are caulking a bathtub). Others claim a little spit on the tip of your finger is the best method of shaping the surface and getting a rapid cure. -jim |
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