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Mon Jun 30, 2008 6:18 pm

I saw that same illustration with the grooved plunger that Bruce mentioned above in the Type 3 and Type 2 books when I checked this afternoon.

Mon Jun 30, 2008 7:21 pm

I've seen mis- information in books ( even the Bentley manuals) as well as all over the internet! ( just saying! :wink:) I have seen pictures and descriptions of things WRONG in several areas. Many have been brought to light in threads on this site.

I have seen them installed in some dual relief cases but it was the aftermarket kits...

I do not recall ever tearing down a known "original" dual relief 70 and later engine with that style piston in it. I have probably torn down a good 30 or more engines I know for a fact were original to the car and never rebuilt or had much more than routine service done.

But... who knows?? maybe the factory/engineers thought better of it later??? :?

Anyone know if Jake Raby or anyone who has done some extensive testing might have tested to see if there was/were any benefits or problems?

Mon Jun 30, 2008 7:55 pm

Yeah, I'm pretty sure I've never seen an original grooved plunger in a dual relief either, just aftermarket ones.

I know Muir mentioned the grooved plunger in the Idiot book, but I can't recall what he said about it other than it routes more oil to the cooler. I'm not at home to look that one up right now. I don't seem to recall if he talked about single/dual relief on it though.

Mon Jun 30, 2008 8:29 pm

One problem with Muir's book (though I love it and recommend it highly) is that in trying to patch in changes for each new year and model, he ends up with some incorrect "landing spots." Advice that once made sense can be incorrect for a later model. He got a little careless on which change happened in which year (although he cautions us about that). I think the grooved plunger falls into this category-- advice that made sense for many editions of the book, but that do not apply to every case now.

Sat Feb 06, 2010 5:51 pm

wait so is the dual oil relief valve for like dog house coolers or some thing?

Sat Feb 06, 2010 6:58 pm

I am probably way out of my league here compared to the other contributors to this thread but i'll give this a shot..

After reviewing the flow diagrams it looks like VW recognized an opportunity to improve oil cooling without changing the case casting when they introduced the grooved piston. They must have determined that there was more than enough pressure in the oil galleries when the engine was hot that they could afford to add a secondary path back to the sump, thereby increasing flow through the cooler without compromising critical component lubrication requirements. Problem was, I'll bet they learned that as the engine clearances and oil pump wore the front bearings would begin to starve as a consequence of the secondary path so they created the dual relief case. With this design they satisfied both the need to flow as much oil through the cooler as possible under various conditions and keep the pressure as even and high as possible in the galleries at all times.

If my theory is correct you probably should not use a grooved piston in a dual relief case as this will to one degree or another defeat the purpose of the front relief which is actually a regulator or bearing wear oil pressure compensator.

What do you think? I'm open to criticism. I am pretty new to this stuff, just throwing it out there.

Sun Feb 07, 2010 12:13 am

anyone have any pics or measurements for the actual VW grooved piston? How can you tell the difference between the og and aftermarket part? Spring differences??

Also Ive seen the aftermarket booster in action, only use it if you have an external cooler and filter with A LOT of tubing. If you use it on the stock doghouse cooler it will burst. A buddy of mine had one in an engine he bought and kept blowing stock filters till he got rid of the piston and put a stock one back in.

Sat Mar 20, 2010 10:39 am

I know this posting is a bit old but instead of posting a new one this hits home for me. I too have a 1776 cc motor that runs warm. I put in the oil pressure booster kit which did boost oil pressure above idle but didn't help cooling. Looking at the diagram in the Bentley manual, I think the groove in the pressure relief valve seems to redirect oil away from the cooler when pressure is too high. So theoretically that should increase temps. Has anyone ever just installed the piston with the stock spring or vice versa, and what was the result?
Thanks

Sat Mar 20, 2010 11:41 am

Russ Wolfe wrote: VW themselves did not use that plunger with the later dual relief cases, even though they had it available. I am thinking, that it should NOT be used in a dual relief case.

i think i remember reading in a bently manual one time that it specifically said not to use teh grooved piston in a dual relief case

Sat Mar 20, 2010 7:51 pm

sbeetle79 wrote: Looking at the diagram in the Bentley manual, I think the groove in the pressure relief valve seems to redirect oil away from the cooler when pressure is too high. So theoretically that should increase temps. Has anyone ever just installed the piston with the stock spring or vice versa, and what was the result?
Thanks

All three Bentleys (type 1, 2 and 3) that cover dual relief cases all have the same photos and similar charts (the type 2 also covers the type 4 Bus engine) where it shows a grooved plunger in image 1301, but not in the other diagram and photo. No actual mention of the grooved plunger is made in those books. And I think that retouched photo showing the grooved plunger is incorrectly used there. It could be some other Factory manual discusses it better than the USA/Bentley publications do.

Now, in the single relief 66-69 Type 1 book, it does mention the grooved plunger though:

which echoes what was said in the older VW1200 Workshop Manual:

Sat Mar 20, 2010 9:23 pm

Here's a good article from a book that shows an engine block cut in half, one a single relief and one a dual relief plus a detailed description on the relief valves. It seems that the port to drain oil back into the sump from the pressure relief valve was deleted after adding the pressure control valve which does that same function. So I don't think the groove does anything anymore.

http://books.google.com/books?id=bdG4s_di9bAC&...mp;f=false