Saturday, 19 March 2016

Cavitation and other fun things

I've spent the last week or so trying to sort out a few things. Among them was a bunch of oil leaks. Some of it was me not tightening things enough, some of it was... werl, being an aircooled VW. At the same time I've been facing an ongoing issue with the intercooler system. It should be logging intake air temps (IAT) about 10deg higher than ambient. Instead, the other night when I went out driving on a 22degC evening, the IAT was 47degC. Head temps are fine, but the intercooler is not working as designed.

I came to the conclusion that the issue had something to do with airlocks or the pump. Today I ran the pump on it's own to see how much movement I had through the filler neck. The answer was, "none". I spent a while squeezing hoses and the like but still no luck. So then I started cracking coolant hoses at joints. A whole bunch of places had fluid but it wasn't moving. The outlet of the pump had foamy coolant coming out. This means there's air somewhere in the system and the pump is cavitating. Jacking up one side of the car helped it suck up some more coolant, but it still wasn't working.

On the advice of a friend, I tried this... getting the pump to pull water up out of the bucket.

No cigar. No cigar at all. Even when I put a garden hose into inlet hose it wouldn't pump water out at any pressure. So after a bunch of stuffing around, I pulled the pump out. The good news is, the pump actually works. It works well. I came to this conclusion... the pump is in the wrong place. First up, it's a centrifugal pump and doesn't self prime. Second, it was mounted with the inlet pointing down, halfway up the cooling system.

In short, it was always gonna be a fail. Sadface. So neat, but so useless.

So, what to do next? So I started climbing around the car and trying to figure out where to mount the pump and how to mount it so I could get coolant to it. Oh what fun. There wasn't anywhere in the engine bay I could find that the pump was going to fit. There's already so little space in there. Even if I could get it in there, getting the hoses connected to it and mounted is next to impossible. So I started looking under the car...

Oh man, so much junk under one car...

So after agonizing for a while I figured, "what about where I mounted the oil filter?". And amazingly it worked.

I'm beginning to understand how Porsche ended up with ridiculous tea tray spoilers and the like. I'd rather not put the pump in the rear guard except for a few things...

1. It's at the lowest point in system or close too.
2. It hangs directly off the bumper mount.
3. All the fluid should drain directly into it so it bleeds itself.
4. The oil filter is there on the other side and works ok.

Now all I have to do is run some hoses and re-route the wiring. Time to call Emil again.

No comments:

Post a Comment