996/997 Coolant Pipe Welding
One of the major issues that plagues the Mezger engine found in 996/997 cars is the metal coolant pipes that live under the intake manifold. In factory orientation the pipes are press fit into each other and mated together using glue. There are a couple of problems we have seen with this method of joining these pipes together. One issue we have seen is that the tollerances for the pipe fitment is not always perfect. Sometimes they are too large and leak, other times they are very tight and do not allow the inner pipe to come out, both have proven to be an issue. Another issue is with the glue itself, over time with heat cycles the glue will no longer hold and the pipes will eject from the cast
Residue from the factory glue.
piece. Now, this does not sound catastrophic does it? Just a little coolant leak, right? Well, imagine you are on track (or the street for that matter) and one of these coolant lines desides it doesn't want to stay put. What happens is the coolant system becomes very empty, very fast. This causes a massive smoke cloud behind the car and a lot of coolant on the track/street. This can be a problem for both you and the person driving behind you. Typically the person behind you takes the brunt of the hit
and ends up spinning out. Now, there area couple of different solutions to this issue, both involve engine removal. One solution to this issue is referred to as 'pinning' the coolant pipes. What this means is that a hole is drilled through the cast pipe, as well as the insert, and then the hole is tapped (this creates threads for a bolt) and a bolt is installed with
loctite. This is a low cost and effective solution, however, this is not permanent in our eyes. Over time the loctite will fail and there will eventually be a leak. Pinning has been inspected after 50k miles and there have been no issues. This is certainly not the 'wrong' way of doing it, but given that these cars are not going anywhere, we believe a weld is the permanent solution. All of that being said, welding does come with it's own issues. We have seen failures with welding as well, the issue stems
Inner pipes removed from cast pipes.
from the quality of the welds. If there are any mistakes or issues with the welds they will not hold and will cause a coolant leak, the welds here have to be perfect. Our welder is FAA certified and welds aerospace parts every day, we have yet to have a single issue with any welds on the many sets of coolant pipes we have done. These welds/pipes have been tested and thoroughly exposed to severe track conditions with no issues what so ever. We are confident in this repair and stand behind it. If you have a Mezger powered 911 feel free to give us a call and we can go over any questions you may have. This is an essential repair for these vehicles, especially as they get older. We typcially reccomend doing this job with a clutch so the customer can take advantage of the labor. The pictures below were taken of a set of coolant pipes from a 997 GT3.