This issue is with regards to my 1996 Mercury Villager Van. I know its not a Mercedes, but I am thinking this is a universal issue that could apply to any gasoline car. Plus, I cut my "car repair teeth" on my 300 SD (and I use this site frequently) so any help is appreciated. My continuing service on my 300 SD awaits completion of this car, since I do not like to work on 2 at the same time....

Here's the scoop: I am wanting to sell this van, but it started a funny vibration which turned out to be a "knock sensor." This device lies deep in the car, beneath the upper and lower intake manifolds and beneath the "coolant crossover tubes." Given the $1000 + repair bill I decided to attempt it myself using the Hayne's manual for this car. It was the largest car undertaking I have ever taken on (I think) and it was a lot of effort. I had to empty the coolant before beginning this task because the lower manifold as well as the coolant crossover tubes are part of the radiator cooling system. This is all new to me...

Anyway, I successfully replaced the knock sensor and put it all back together again. For some parts of the car this required using RTV to make a seal between different parts of the coolant crossover tubes and manifolds that mated to other parts. My concern was whether the seals I was repairing were going to hold... I knew of no way to test these seals along the way...

Once I got it all back together again and refilled the coolant and started the car (yes it did start!) after about 45 seconds I started to hear a hiss and saw some steam. This happened every time thus far, so I am fairly certain that I have a leaky seal.... And it seems to be deep down

Question 1: I know that radiator shops can test these systems for leaks. Is there a way to do that with the coolant in? If not, is there a way to do it with the coolant out?

Question 2: Assuming there is a leak, how can I tell where that leak is located?

Question 3: I assume I need to pull everything out again and reseal the suspicious joint(s). Is there a way to test these on the fly so that I do not have to repeat the procedure yet again?

Question 4: Do I need to replace the new gaskets that I had just put on for the upper and lower intake manifolds? I am assuming those aren't the problem, but they are now sandwiched between the manifolds as they are supposed to be and all bolted in at the proper torque.

Question 5: Any tips on removing the coolant and fuel injector rubber lines? Even the new ones are a bear to get off and on (especially the short ones that attach between manifolds) and some of the original ones I had to cut to remove. I'd rather not cut these new ones, but will if I have to as I dig back down.

On the bright side, I know that if I have to dig down again it will take me far less time than the first time I did it last week.

One other thing I did that maybe I shouldn't - I made a gasket at one location that had originally just been RTV'ed (and its deep down at the coolant crossover line junction). So, I both gasketed and RTV'ed that junction. That may be what caused this whole problem, but I'd like to be able to verify.

I apologize for the long winded-ness and I hope this is relevant to any other discussions on this thread.

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dannyf
1984 Mercedes 300 SD 214 K miles. Runs on WVO ~ 22 mpg over 8 K on WVO
1997 VW Passat TDI 156 K miles. Uses biodiesel and diesel. ~ 41 mpg
1996 Mercury Villager gasser. ~ 20 mpg