...and apparently, it is.

Today, I changed the coolant bypass hose, and in the process, replaced the gasket that goes from the block to the back of the t-stat.

I forgot to buy a gasket, and no one locally carries it, so I bought a roll of gasket material, and made my own (pics to follow, once I lose this grumpy attitude).

I used gasket sealer on the block side, then bolted everything back in to place. I didn't even get to start the car - just using a hose to run water through the t-stat showed a pretty significant leak coming from that gasket, on the back side, closest to the driver.

Needless to say, I wasn't a happy camper. I removed everything, re-applied more sealer on both sides of the gasket this time, and I'm leaving it overnight.

Any other ideas why this things continues to leak?

Oh, and, by the way...that hose that I replaced? It leaks too...out the top, even with the straps tightened down as tight as I can get them.

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1984 300D: 275,000 miles (soon to be for sale)

In search of my 1987 300D in anything but white.

Did you perhaps place the upper hose clamp too close to the bead on the housing nipple? And there is a such thing as too tight when it comes to hose clamps, although that is a pretty hefty hose if you used the one intended for that purpose.

Perhaps - I will take a look in the morning. It doesn't seem "too tight" on that hose, although I can't get it much tighter. Maybe re-seating it on the hose will do the trick.

Any ideas on the gasket going to the block, Tango?

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1984 300D: 275,000 miles (soon to be for sale)

In search of my 1987 300D in anything but white.

What type of gasket material did you use? The proper gasket is very thin paper. That said, there is no reason that a field fabricated gasket shouldn't work.
For a different option, Permatex makes a RTV gasket material specifically for cooling systems. They claim it works great; I have never used it except to coat a paper gasket, however.

http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_makers/Permatex_Water_Pump_Thermostat_RTV_Silicone_Gasket.htm

Hmm...I bought a roll of gasket material that was said to be rated for water, and recommended for areas like the water pump. I believe it was called rubber cellulose. It's pretty darn thin, but maybe I should go back to Autozone and by the paper-like stuff...brown in color, I believe.

Flippin' gasket...I'll show him...

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1984 300D: 275,000 miles (soon to be for sale)

In search of my 1987 300D in anything but white.

sure you got everything really clean? and tightened everything so it goes down square, not tilted as it seats.

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83 300SD Dark Silver Dark brown inside

I mean, shoot...I used a toothbrush once I scraped away all the crud. It seemed pretty clean to me!

Attached Thumbnails

 

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1984 300D: 275,000 miles (soon to be for sale)

In search of my 1987 300D in anything but white.

I used Permatex sealer, and the rubber cellulose gasket material.

In the picture, the one on the left is my template made out of office paper. I traced the outside edge of the housing with my kids chalk, then pressed the paper on the housing to leave an imprint. I darkened the trace line with a pencil and cut it out for my template - transferred it to my gasket roll, and voila!

Attached Thumbnails

   

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1984 300D: 275,000 miles (soon to be for sale)

In search of my 1987 300D in anything but white.

Maybe that gasket material to too thick and spongy and it's squeezing out from under the housing. If it's leaking while not under pressure, the leak is pretty significant.

It looks like you did good job duplicating the gasket though.

Yeah, I suspect some grime on the sealing surface. I use a wire brush and like to see shiny (like new) metal at least a couple of mm thick all the way around. The OEM gasket is paper as previously mentioned.

I had the same problem with the bypass tubing. My leak there was caused by hose clamps that weren't lined perpendicular to the tube...it should orbit the tube like a planet not like a comet --- if that makes any sense.....

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Not trying to be a buzzkill or anything but just get a real gasket. go to your local European mechanic shop and they'll get you one the same day.

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1981 300SD 512k OM603

Man, who invited Buzzkill to this party?

Yeah, I checked with my preferred Euro parts supplier, and two back ups - none of them had it in stock. True, I should of had the foresight to get one ordered last week while my car was up on ramps, but alas, I did not.

So, I was stuck making my own yesterday. And now, staring at work tomorrow morning...my wife says she'll kill me and my lovely car if I don't have it fixed, so I don't have to leave her without her Honda Pilot all day again.

Let's see if I can't get that thing fixed today...

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1984 300D: 275,000 miles (soon to be for sale)

In search of my 1987 300D in anything but white.

I'd forget about using the gasket you made and use one of the permatex form-a-gasket liquids suitable for machined surfaces if you don't have access to the stock gasket. The stock gasket is literally paper thin and the mating surfaces are made to seal to it without any sealant, so if you use a form-a-gasket product in place of the paper sealant you should be good to go.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

My eyes are getting old but from what I could tell from here that gasketed surface you showed a pic of is not ready for a gasket installation. Clean it up with a wire brush and use an oem gasket.

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Jim

It's hard to be positive but there might be some hard buildup on the inner coolant channel edges protuding denying you a seal. Not to seal with your gasket under no real fluid pressure something is obviously wrong.

I would cautiously dress the surfaces or at least check them carefully with a small piece of glass or some form of straight edge. The toothbrush approach might not be strong enough medicine to deal with any calcified type of built up material.

Check both parts carefully for any obstructions to flatness. The gasket will deal with any small irregularities. Not major ones though. Also clean the parts well and examine for cracks in the metal if you find your gasket surfaces flat by test.

If the leaking nipple is corroded or otherwise not smooth a silicone will bind well to the rubber and seal irregularities there usually. Use a higher temperature silicone for piece of mind if you wish. Although coolant fluid temperatures in operation are usually no higher than around 220F. Give the silicone enough time to cure if you decide to utilise it on the nipple connection.

The correct way to do this in my opinion is to apply some silicone to the nipple. Slide the hose on and only snug the clamp until the hose does not slide on and off easily. When the silicone cures then tighten down the clamp. This compresses the silicone that has filled in any irregularities that were causing the leakage.

I ran a series of tests thirty years ago to establish what glues etc bond well to various substrates. It was for the construction of our solar system that is still in pretty flawless condition after those thirty years of service. The first thing we learnt was that silicone based adhesives form a somewhat strong bond with rubber. By the same token they also do not bond well to certain metals at all. We found we needed a precoat or primer of epoxy on almost surgically clean metals before we obtained the required adhesive effect to our satisfaction for the silicone . The trouble to accertain the various adhesive effects has served me well over time on many occasions.