@JasonC posted:There has to be some correlation between oil temperature and cylinder head temperature
Ideally and generally, yes. 10 years ago, I would have argued that they were inextricably linked, but there are some weird instances (running in a high load, low RPM situation, in the mountains in a high gear, as an example) when they decouple and oil temperatures stay fine, but CHT goes nuts.
5 speed guys will never see it, but if you’re a 4 sp (with a 3.44) man, it’s quite possible.
@JasonC posted:Indeed, the Texas heat is quite severe this summer.
...Notably, the faster I drive the hotter the oil becomes, so at some point I may be forced to slow down. However, I'm running 10W-30 Valvoline Classic/Racing oil, which is synthetic and will maintain its lubricity properties at temps way above 300^0 F. So I SHOULD be ok even at elevated oil temps. Perhaps I'm missing a temperature failure that's not oil related?
Jason
Generally, if a VW engine's oil temperature is much above 225-230° F. for any length of time, the stock magnesium engine case's temp can get well beyond it's design parameters which will eventually affect it's structural rigidity. It doesn't happen overnight, but run it often enough at those elevated temperatures and it's a recipe for disaster. It isn't the oil- it's the case's design/structural limitations that we're working with here.
Do enough reading and you'll find that some people's engines only last a fraction of what most people consider 'acceptable' life for the combo- I've seen someone I know's hot 2 liter turned into junk in 9800 miles- the case no longer had oil pressure at idle when at operating temps and the heads were so overheated they couldn't be rebuilt. The middle main bearing web was spread (classic case overheating failure- a replacement case was required) and the guides were falling out of the heads, so they were junk as well. And this happens more often than you think.
Build a well matched, streetable combo with solid parts, make sure the tune (carb sizing/jetting and ignition timing) is right, don't constantly drive the bag off it from the moment it's started to when it's shut off, manage it's OIL AND HEAD temps properly (this quite often means installing a thermostat controlled oil cooler and introducing more air into the engine compartment to carry away heat radiated off of the engine so the carbs and cooling system isn't consuming pre-heated air), change that oil regularly and these things can last a long time.
A couple of easy ways to tell what's going on- if the cylinder covers are so hot you can't hold your hand on them for more than a quick touch, you probably need more airflow into the engine compartment, and if a drop of water (or spit) sizzles on the top of the engine case- it's getting too hot!
VW never built (or even dreamed of) Type 1 engines with the power levels we get out of them today and there's no factory engineering/cooling solutions for the extra heat they produce, so you're the engineer in charge of keeping it alive. Sadly, too many guys, after building their high perf VW engine, start it up, decide 'yup, it runs real good!' and drive off, never considering what it really needs to live a long, happy life.
Hope this helps. Al
@JasonC posted:Well I took a peek at my fan with a mirror and flashlight today, but I cannot see where the blades penetrate the flange as shown in your picture.
Jason
You won’t be able to see the ends, but you can see the “root” of the vein, where there’s a little dab of weld where the vein meets the backing plate.
So, back to the original post, this is a VMC speedster with a Pat Downs 2332 engine. I'd quit trying to guess and give VMC a call. Anna should be able to give you the scoop on whether the fan is welded or not. I can't imagine a Pat Downs engine leaving the shop without a welded fan, but...
I don't think I've seen another exploding fan on this site, but it happened to mine at 5600 rpm. The fan was new, 15 years old, and unwelded. Give Anna or Greg a call.
I have a VMC with a Pat Downs 2332 and experience the same chirp on first start up from cold. It happens when I pump the gas pedal once before cranking it which almost guarantees immediate ignition. I think your hypothesis of the initial ignition being a bigger bang as the culprit is accurate.
Because I want to avoid the chirp, I tend to (from cold) turn the key and let it crank once or twice, let off, then give it half a tiny bit of gas and crank it again. I don't know if its fact or not, but this gives it a much more gently ignition and the engine more slowly comes to life. No chirp
On any warm startup, I just crank it without any gas and it'll come to life after a few cranks.
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Looked at my fan, but couldn't hold the light, mirror, and phone all at once, so dug up this photo from the interwebs and added some arrows.
This is what you'll be able to see, and the welds should be pretty obvious if they're there. All of the vanes should be welded.
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I've never noticed welds there, Mitch- the ones I've seen have always been on the tabs on the outside of the assembly.
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Al, maybe you drilled them all out?
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@Sacto Mitch posted:.
Al, maybe you drilled them all out?
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Ok, I laughed out loud at that!
@ALB posted:I've never noticed welds there, Mitch- the ones I've seen have always been on the tabs on the outside of the assembly.
You can see the backside of the welds. This is what @Sacto Mitch is talking about.
@Michael Pickett posted:So, back to the original post, this is a VMC speedster with a Pat Downs 2332 engine. I'd quit trying to guess and give VMC a call. Anna should be able to give you the scoop on whether the fan is welded or not. Give Anna or Greg a call.
Thank you; I will.
Jason
@LI-Rick posted:You can see the backside of the welds. This is what @Sacto Mitch is talking about.
I can see what appears to heat related discoloration on my fan blades.
Jason
@ALB posted:Generally, if a VW engine's oil temperature is much above 225-230° F. for any length of time, the stock magnesium engine case's temp can get well beyond it's design parameters which will eventually affect it's structural rigidity.
My engine cases are made from aluminum and will behave differently (hopefully for the better) compared to magnesium cases under high temperatures.
Jason
That's a big advantage to the bubble-top cases, but hopefully you don't get the oil hotter than 230 deg or so.
