Overheating problem in TD bus

[Rabbit on Roids]

they made a special air cooled engine? i thought you had to build one yourself to get any real power out of them?

Well, that's what I mean -- no original air cooled pushrod Porsche engine would stay with my oil burner 

For the cars that have been highly tuned, or powered with big built VW type 4 engines, or even 911 six cylinder lumps -- that's a different matter!

Yea, i kinda doubted that they made a ac motor that would skool your oil burner. unless, like you said, it was heavily tuned, or swapped.

[speedy]

I added a bleed hose right where the coolant exits the head and routed it to the overflow tank.  I then blocked off the bleed hoses from the rads as I no longer think they are necessary in this application (rads mounted flat under the floor are nowhere near the high point of the system).  Unfortunately, the bus still overheated. 

Tonight, I removed the thermostat and tested it on the kitchen stove.  It seemed to open a bit late (190-ish) but otherwise seemed to work.  It was stamped "Made in USA", must be an old one.     Maybe it's a 192-degree thermostat?  Just for fun, I put the system back together with no thermostat and drove it about 15 miles, mostly at WOT.  It ran just fine and did not show any signs of overheating.  So, I'm hoping that means that the head gasket is okay.

The temp stayed about 170 most of the time and topped out at 180 on a long stretch in 4th gear into a headwind.  It's about what I would expect considering that the engine is getting a mix of cooled and recirculated water and that the outside air temp is 35 degrees.  Took a long time to warm up of course.

 I drove to Autozone and got a new 180-degree thermostat, guess I'll install that and try to overheat it again.

-David

[Wayland]

Fwiw, I bought a Caddy with a blown head gasket a couple of years ago. I tried to drive it home, but it overheated every few miles. I removed the thermostat, and was able to make it 12 miles home without the motor even heating up. I don't really know what this means as far as your cooling system problem goes. Do you get alot of pressure in your header tank after only a few momoent running? If so, you may have a headgasket issue.

[speedy]

Hmmm... well I suppose I may still have a blown head gasket then.  After my 15 mile drive last night, there was only a small amount of pressure in the overflow tank - about what I would expect from a warm system.  With the thermostat in, there would be a lot of pressure after driving a few miles.

-David

[speedy]

I had previously run the bleed hose from the top of the cylinder head to the overflow tank.  Yesterday I put in the new thermostat and drove my usual 10-mile circuit around the local farm-to-market roads.  No overheating.  Today I tried a more ambitious 40 mile jaunt up the interstate.  I was driving into a North wind going 60-65mph, 800-1000 degrees EGT (pre-turbo) and 8-10psi boost depending on the slope of the road.  Went a dozen or so miles this way and just when I was beginning to feel good about things, the temp shot up from 195 to 230 - same crap as before.  I pulled over and got out, observed steam and water coming from underneath the bus (via the pressure cap on the overflow tank).  I drove gently to a safer spot and let it idle for a few minutes.  By the time I got the engine hatch off all of the pressure was already vented and the temp was back down to 190.  I added about a pint of water and got on the highway going back towards home.

Cruising 60-65 again (but with much less pedal since I now had a tailwind) I again saw the temp shoot up to 220 but it almost immediately went down to 210 and I was not by an exit so I just kept going.  I slowed down to 55mph and the temp bounced around a bit more before settling back at 190.  I drove all the way home and it never went back above 190 the whole way.

I need to decide whether or not to go ahead and change the head gasket.  I would start tonight if I was sure that the head gasket was the problem, but I still have doubts.  I don't think there was any air in the system when I started the drive, so it either came from the head gasket or from water boiling in the block.  If water was boiling in the block, that would have to be from inadequate water flow.  I guess I could try a new water pump.

A couple of other things - the engine has been getting harder and harder to start.  Used to start and idle smoothly after 8 seconds of glow, then it started but idled roughly, and lately it has taken 2 or 3 glow plug cycles before it will get going, with plenty of smoke.  Still runs like a swiss watch when warmed up.  Could this simply be because it has only seen short trips around town the past two years?  Or could it be another symptom of a bad head gasket?

I need to drop the drivetrain soon anyway to replace the tranny, how hard is a head gasket replacement if the engine is sitting on the garage floor?  Any hints for a first-timer?  I have replaced head gaskets on other OHC 4-cylinders before, I assume this one is not much different - remove timing belt, intake/exhaust, valve cover, injector pipes, water hose, head bolts?  If the head surface passes the straightedge test, can I just put a new gasket on it and put it back together?  Maybe I will just do it and get it over with, but I want to make sure I'm not opening Pandora's box.

I read all of the info about the various head bolts and I think I would probably just get the factory Torque-to-yield type since this is a stock engine.

If I replace the gasket and it still boils over, I am going to... <ahem> have very negative thoughts!  Thanks for any wisdom you care to share.

-David

[speedy]

I think the reason they made the overhead hatch the size they did was that in 1973 (the first year of the hatch) the only things that were serviced through the overhead hatch were the air filter and carbs.  Everything else was serviced through the rear hatch.  When the Vanagon came around, it had no rear hatch so a lot more stuff had to be serviced from the overhead hatch, therefore they made it larger.  If any of you know a guy named Yannick Galipeau, he did a pretty nice job of enlarging the hatch in his baywindow to Vanagon-size.

Question - if you have everything at TDC (or at any other specific location, for that matter) when you remove the head, why would you have to worry about valve-piston clearance on installation?  Assuming nothing rotates, nothing will touch, no?

If the head needs work, I am going to be in trouble.  I don't know if there is anyone in Dallas/Ft.Worth that does VW diesels.

Thanks for the reply,

-David

[speedy]

I went ahead and replaced the head gasket.  Put on a new two-notch gasket with the Escort Cosworth ARP studs.  While I was at it I re-shimmed the valves, had the injectors rebuilt by a local shop, pimped my glow plugs and installed a rebuilt tranny with 10% taller gears.  I should have been able to do all that in a month, but it took me ten!

But the end result is no more overheating.  I am so relieved.  Thanks to everyone who took the time to reply and especially those who helped me with questions that came up during the job.  The turbobus is running like a Swiss watch and I can't wait to get some real heat... and an intercooler.

-David
 http://motorheads.net/vw/turbobus

[rabbitman]

Well that's handy when fixing stuff is actually successful. Good job.

[Vincent Waldon]

Seconded.

And I've gotta say yours has been one of the more entertaining build pages... I've kept my eye on your site as you've moved along and definitely have enjoyed your exploits.