TheSamba.com :: View topic - Why is 70-75 mph so bad???

Fri May 30, 2003 9:24 pm

I just got back from my very long trip in my 72 camper. My bus would do 70-75 no problem and I even got it up to 85 once on accident, not paying attention to speed. Now, I kept my bus at 65 most of the trip because thats what everyone says to drive at, and not that I care because 70 is only 5 miles faster and really isnt going to get me anywhere much faster. I am just curious though, why is it so bad to run higher than 65mph. My bus ran fine at 70 and it did not seem to make that much of a difference in drivability. What really is going to happen if you drive past 65 for long distances.
One more question, I only burned about 1 quart of oil for every 1000 miles. Is this good? I thought I would use much more than that. Did I just get lucky and have a great running machine? Thanks.
matt

Fri May 30, 2003 10:57 pm

It's not a huge problem and the engine can handle it as you experienced but there are long term consequences for engine life. You can decide how you want to drive the bus.

Notice how easily the bus cruises at 55-60mph but when you let off the gas from 75mph it wants to slow down very quickly? VW did their best to make the 2nd generation of busses more aerodynamic but it still has a 0.43 cd which means that after a certain speed which is much earlier than for the average passenger vehicle most of the strain put on the engine is required to fight the wind resistance. Some facts:

- air-cooled essentially means oil-cooled
- the crank-driven fan is effective up to somewhere in the midrange rpm range
- multi-weight oil viscosity is rated at 0F and 212F
- high oil temps drops the oil pressure
- the engine parts expand as it's heated
- oil temperature is partly a function of ambient temperature
- the stock engine wasn't counter-balanced

What's the verdict? It depends on the engine condition and the temperature. Going 75 in winter isn't as bad as going 70mph in the dead heat of summer but either way if the oil temperature is 250F due to driving habits then you are doing the motor a disservice.

You really need some gauges to tell you how the engine is doing and keep within the rule of thumb guidelines that people have developed for Type IV engine longevity. If you don't, you'll be rebuilding it sooner but who can predict exactly when that will be?

At those speeds, that oil consumption isn't out of line at least according to VW but I think it shows that you are running the engine too hard.

Sat May 31, 2003 1:10 am

Stock Bus engines were not designed to go so fast. Quicker engine wear will be the result.

Sat May 31, 2003 8:01 am

I drive mine most everyhwere floored. What kills your motor is lugging that doggie up hills with out down shifting. Keep and eye on the temp and keep it from boiling. I really don't wee any problem in deiving that thing as fast as it will go.

Sat May 31, 2003 8:47 am

70-75 shouldn't be a problem with a 72 as long as you change that oil every 3,000 miles and follow vintage's advice. Lugging them really is the death of the engine.

Sat May 31, 2003 10:32 am

I don't know about a '72, but the owner's manual for my '79 says cruising speed is 75 mph. Just make sure you have a sump oil temp sender and a guage up front. As long as you drive within the healthy temp range, you should be just fine at 70 or 75 mph.

Richard

Sat May 31, 2003 11:30 am

Full synthetic oil helps a lot. Castrol Syntec 5w 50 is the ONLY oil I'll use. Period. In a really worn or leaky engine, it isn't worth it, but any engine that runs well is a candidate, no matter how many miles are on it. Don't buy the crap that it'll cause problems, or will ruin a high mileage engine. It won't. After a few thousand miles, you'll be surprised at how clean the engine is in the valve covers. Initially, you may go thru a quart or two really fast, as it's cleaning and reseating everything. I even run this in diesel Benzes. You'll notice that the engine runs quieter and cooler almost right away. The second thing is to use ORIGINAL German filters, with the proper checkvalve in the bottom. (If your bus takes one.) Hydraulic valve people will soon realise that there's NO initial valve chatter in the AM.
As to driving speed, here's my general rule for what it's worth: Let the Bus do what it wants. If it wants 75, 85 or so, that's OK. NEVER push it beyond what it wants and you'll be fine. My last 79 Westy would cruise all day at 80. Back to synthetics for a final thought: If you try and like the motor oil, consider a Royal Purple or Redline synthetic transaxle oil, too. If you have an auto, try Royal Purple Synthetic Max ATF. Just make sure your auto doesn't leak, or it WILL get worse with the Max ATF.

Sat May 31, 2003 3:47 pm

Nothing but Castrol for me too...

Richard

Mon Jun 02, 2003 3:51 am

What synthetic oil weight would be good in 90 to 100 degree texas weather? I have always used 20w 50 regular oil. What would be the best oil for our hot weather down here?

Thanks James

Mon Jun 02, 2003 3:50 pm

Your owner's manual should have a little chart with recommended weights for a given temperature range...

Mon Jun 02, 2003 8:21 pm

Wavepimp, Castrol Syntec 5w50 will handle it ALL- really really hot, or really really cold. It's fan- freakin'- tastic. It REALLY is 5w50- that's NOT a misprint. They make other weights as well but this is the best.

Tue Jun 03, 2003 4:07 pm

Well, here's some vague info that someone else might be able to shed some light upon and explain better. When an engine is operating at 5000 rpm and changes to 6000 rpm, the increase in stress on the engine would logically be an increase of about 20%. However I was reading somewhere that this isn't the case at all. The increase in stress on an engine from running between 5k and 6k rpms is something like 90%. I'm not sure how this comes about, but I specifically remember reading it on another forum. I wish I could explain it better, but I can't. Hope this helps some.

Tue Jun 03, 2003 7:31 pm

the hydraulic lifters don't like the rpm range too far above 5000 rpm. rpm and heat are what I use to gauge the speed for my bus.