new tranny causes external oil cooler to stop working?

[DrElch]

Hi Guys,

Here's my situation:

- 72 BayWindow Bus
- 2400cc Type4 Engine - fairly tame setup, made for torque not revs. runs well
- rebuilt transmission with very tall 4th gear for smooth autobahn cruising (I'm in Germany)
- External Oilcooler under front skirt + Mocal Sandwich Plate (Has been a well proven actor so far)
- STD Type4 Oilpump

I've had this engine for a while and it has been driving fine so far. Oil temperature and pressure always fine. The oil cooler setup was just working. Mostly temperatures between 90 and 100 degrees Celsius (194-212 F) if not pushing hard. All good.

This season I have swapped the transmission for a new one with a taller 4th gear, because the I had the original 1700cc Transmission in my bus and therefore the RPM at cruising speed of 110-120km/h (68-75 MPH) was simply to high. There was not really any other reason for this rebuilt.

Since then my temperature situation has changed. The engine revs much lower, but the temperature went up to more like 110-120 ( 230 - 248 F) if going between 110-120 km/h. Tendency rising. Slowly but surely rising. I was able to control it if I just reduced my speed to more like 90-100 , but I knew that something was fishy.

Checked the basic stuff:

- Oil is fine and new (20W50)
- All hoses and linkages are fine
- Carbs are well setup
- Valves are fine
- Ignition is fine

Then I checked the external oil cooler and oil filter: Both were quite cold after such a drive. That's bad. I suspected the Sandwich plate.

- Removed Sandwich plate and checked it in the oven: Thermostat closes as expected

After that I put the plate back in and did more testing as I started to suspect the new transmission.

So I went for another ride on the highway and after reaching roughly 115 degrees celsius I stopped and checked the oil cooler, which was still cold. Okay fine.
Then I continued driving with roughly a speed of 70km/h in third gear to get the RPM up.
And lo and behold, the ext oil cooler went hot very soon after and so did the oil filter.

So what is going on here?

- Low oil throughput(?) / pressure(?) due to low RPM (<2500) at 110-120 km/h in forth gear?
- Low pressure causes the hot oil not being able to push against the cold oil in the oil filter/external oil cooler and therefore shortcuts back into the crankcase?
- Driving with higher RPM like in 3rd gear and 70km/h makes the external oilcooler to get hot. Oilpressure is around 2.5-3.0 bar (36 - 43 PSI). Depending on temperature
- 4th gear and 110km/h will make the ext oilcooler to stay cold. Oilpressure between 2.0-2.5 bar (30 - 36 PSI)


See picture:

So what are my options? Does this theory make sense?

- do I need a larger oil pump (Thinking Maxi-1 of CB Performance here, 26mm sprockets)
- Or is it maybe just that the valve ball/spring in the oil filter adapter (see image) is weak?
- Oil pressure relieve piston?
- Maybe the problem is something else?

Looking forward to your input.

[ekacpuc]

One issue is the 20-50 is too thick unless it’s a very well warn engine. Did you happen to change the oil at the same time as the transmission?

[DrElch]

[Wreck]

you have the same load on the engine but you have decreased the engine cooling fan speed , so your heads and cylinders are now running hotter .
If the oil pressure is over 43 ish psi ,most of the oil will get bypassed back to the sump missing the filter and both your external and standard cooler .

[Zed999]

I run a mild 2.4l in a bus with an additional cooler and oil thermostat in the oil lines, it runs always under 200F (95C). Like you I often cruise at 70mph. Stock pump, cooler without fan under bus near rear torsion tube...

Air lock in those long oil lines to the cooler in the "front skirt? But I'd have thought once cleared it would gone for good. Did you route your lines differently when you refitted the new box?

2500 at 70mph is very slow rpm, my long 4th 6 rib box is at 3500.

[FreeBug]

Well, by reducing engine speed you've reduced fan speed. But there's obviously something else going on. Is this type 4 upright or flat? I imagine it's not easy to put the flat engine in a '72. If upright, try a power pulley.

Where are you reading temps from?

Yeah, that thick oil isn't helping.

And a good synthetic can just about hold at those temps, I imagine.

But none of that explains why you're not getting flow through the ext. oil cooler. Is all the plumbing hooked up in the right flow direction? We've all seen it one time or another, it happens.

The filter gets hot, right?

[DrElch]

[DrElch]

[Wreck]

as long as your oil filter has a bypass valve (most have) you can plug the bypass in the oil filter mount . It would be the first thing I would try .

[Alstrup]

What happens is that at that rpm the stock oil pump has no or very little extra capacity apart from supplying the engine, so the cooler gets bypassed.
Replace the oil pump with a 30 mm unit, go 1 step down on oil viscosity. 15w/40 is good. Then your thermostat & cooler will begin working again.

On the bottom of this page you can buy a nice intermediate plate so you can install a WBX or HD type 1 pump reasoably easy. http://logmech.se/eng/products/engine/oil-pump-hd/ The best is to have another case to do a trial fit in, so you are sure that everything lines up.

Also be aware that if you are taking the oil out at the oil filter bracket, you need to increase the spring tension on the relief spring. The old trick is to take a spring from a type 1 hand brake and cut it so when it is on the table the new spring protrudes into the relief piston and flushes with the factory spring in the other end. It may not be perfect, but it is around right to overcome the increased restriction in the system.

If you have real full flow (which I doubt) there is no problem.

T

[DrElch]

[Wreck]

[DrElch]

[Alstrup]

Yes, of course the bypass needs to be blocked. I assumed that was already done if that was the way you rerouted the oil.

[Wreck]

I started to read about it and also talked to a friend about it who suggested the same. Will try that next for sure.

DO you have pictures of somebody who did it before by any chance?


the 2.3 was done by a professional VW engine builder who turned up an alloy plug that was a slight interference fit ,( he's the person who worked out the issue in our group of friends )
I didn't have easy access to a lathe when I built the 2.6 so I just brazed/ silver soldered small round piece of steel to block the hole in the valve seat . then refitted it (without the ball and spring)
you could tap it out and use a threaded plug but that is over kill since the oil pressure is forcing it in not trying to blow it out like a case galley plug.

[DrElch]

Okay update on this topic:

Got in touch with my friend who happens to be a master in mechanics and he did some magic for me.


Removed the ball and guide from the filter holder

Made a plug out of aluminium with 0.400 oversize of the hole. Technically a m18x1.5 plug would be another good choice for it, but requires some drilling.

Carefully hammered the plug in

Finally plug was fixed in place with some notches between housing and the plug

After that I've put the filter holder back in place and lo and behold, oil pressure was very great between 3-4 bars and oil temperature was very steady around 85 degrees Celsius regardless of conditions and speed. Did a longer run with speeds between 140 and 160 km/h temperature needle didn't budge the slightest.

Btw, I have relocated my temperature sensor. It's not under the pressure relief valve anymore, but under the oil check plate, which seems to be the more recommended place.

Oh and I replaced the oil filter with a filter that had a internal pressure valve. Opted for the "MANN 712/52" filter, in case somebody cares.

Very happy with the results! Thanks to the forum for all the help!

Special shoutout to Lorenz for saving my engines life once more!