97 Passat B4 coolant leak at sensors

On the head, on the firewall side of the head, close to the corner closest to the brake booster.

There are three small sensors of some type, in a vertical row, I assume for temperature. But I don't know why three would be needed, unless they are switches set for different temperatures. They all have a wire terminal held on with a small nut.

There is a lot of pink deposit there, so that is where my coolant loss would appear to be.

I assume that I can back these out and reseat with teflon pumbers tape. Or some other sealant suggested?

I could not find these documented or illustrated in the factory paper manuals. Any explaination of what they do?

These are actually glow plugs that heat the engine coolant. You found your electric coolant heaters. The relay and fusable link is on the firewall next to the master cylinder. The fusable link is under the clear plastic cover.

You should be able to take the coolant GPs out, clean up the holes, and put them back in with teflon tape. Check the GPs with an ohmmeter before you put them back in. They should test at 1 ohm or less. If the coolant GPs test at 1.5 ohms or higher, replace them.

Brian, 97 Passat TDI

I have the excat same problem on my 96 Passat TDI wagon w/ 172K. The bottom of the three sensors is the one that has been leaking. I tightened it a little bit the other day and will check to see if that did the trick. I probably lose 4-8oz. of Dexcool per week which is noticeable when the coolant reservoir goes down to the min. level; not a major problem, just an annoyance.

Thanks to you both.

The manuals sure are lightweight on some things, but heavy to lug around!

Like the long extensive section on the AC that does not document AC charging pressures!

Originally posted by dupp:
I probably lose 4-8oz. of Dexcool per week which is noticeable when the coolant reservoir goes down to the min. level; not a major problem, just an annoyance.

Click to expand...

<font size="2" face="Verdana, Helvetica, sans-serif">Your problem is likely the Dexcool, which is notorious for finding every possible leak point on the engine. Engines that are dry on OEM G12 or Zerex G-05 can develop seepage when changed to Dexcool. From many accounts, Dexcool appears to be significantly inferior to G12 or Zerex G-05 (Long Life).

The engine has VW G12 in it, always has.

These heaters at one ohm each draw around 14 amps when active. This current has to pass through the threads, brass I am assuming at this point, through the threaded interface. I am wondering if this high current is resulting in the failure of the threaded joint to remain 'water tight'. If the threaded joint does not provide a good ground, then there is a differetial voltage across the brass and aluminum which could cause some electro chemical damage. When I reseat these heaters with teflon tape, I will check for resistance from the head to the heater body.

Wow, that sounds like a dumb design.

Are you sure the sealing is in the threads, like pipe fittings, or could it be on a taper behind the threads, like spark plugs? I haven't looked at mine to see. Maybe I should; I have a very slow coolant leak.

Assuming the seal is in the threads, are there other thread sealants that will conduct electricity? I wonder if that stuff electricians use on big high-current connections, I think it's called Alox, would seal threads?

I assume that tapered threads will develop a low resistance contact. I will check the resistance before and after.

I got these fixed. The leaking G12 coolant left a large hard deposit that looked like bubble gum.

The nuts were stainless self locking 8mm.

The heaters are 12mm and have a stainless steel body and heater elements.

The threads are straight and not sealed. The end of the body has a 45 degree taper that is intended to act like a valve seat. I put a thin film of teflom pipe sealant paste on that surface and some teflon tape on the threads just so that they were not bare metal on metal. I guess that never sieze would have been ok to. I checked the resistance from the heater bodies to the battery negative post. I got less than 0.1 ohm (read zero) on my Fluke 77 DVM/DMM. So the grounds are good. The heaters all measured at 0.6 ohms.

The heater body grounds were asd good as zero before I started.

I used a thin polyethelene tube and a syringe to get a syphon going to empty the OF tank, then remove the bottom hose and went down that. Then removed the upper rad hose at the block and went in there an 90 degrees down towards the water pump. I had almost a gallon of coolant out with zero spill when I stopped it.

Getting the coolant back in was not going well, until I used the syringe to pull air out of the vent hose at the top of the OF tank, that worked very well, pulled down the tank level. So I got the job done and did not have to add any more coolant at the end.

It was pretty tight working on the 97Passat. The two that were not leaking were quite hard to break free! The leaker was tight, but less so than the others, consistant with the leaking.