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Engine Discussion of preventative/corrective maintenance and other technical issues regarding your coach's engine.

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  #71  
Old 5 Days Ago
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Randy Dupree Randy Dupree is offline
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You can use a straight through miffler,and it will flow better than the 180 degree reverse flow thing thats on it.
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  #72  
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dan1000 dan1000 is offline
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Did they do the 180 degree thing just to avoid having a tail pipe at the back of the bus where it might get squished? Seems like another one of those "head-scratcher" engineering decisions that our BB's have throughout.
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  #73  
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Quote:
Originally Posted by Randy Dupree View Post
You can use a straight through miffler,and it will flow better than the 180 degree reverse flow thing thats on it.
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Originally Posted by dan1000 View Post
Did they do the 180 degree thing just to avoid having a tail pipe at the back of the bus where it might get squished? Seems like another one of those "head-scratcher" engineering decisions that our BB's have throughout.
Mine has a tailpipe out of the rear corner, shoot out/down about 45 degrees.

My 180 is just the pipe directly bolted to the turbo, get that old muffler out for sure, though.
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  #74  
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Still waiting for WOT fan speed!
Data collected earlier today

Wide open throttle, fan override switch "on", engine fairly cool: Fan measured at 971 RPM.

This post opines that the fan RPM should be around 1300.

Note also: This document describes a Blue Bird hydraulic fan system. It doesn't seem to be for my bus, but I reference it here in case it is ever of use to anyone else. The tables at the end all imply a WOT fan RPM of a lot higher than what I am seeing.

Furthermore, this diagram (which is from page 118 of this parts catalog) from this thread on the other site may be of interest to some. (admin -- please delete this paragraph if referencing the other side is discouraged).

I'm beginning to suspect that the pressure relief valve in the hydraulic fan system is maladjusted, or malperforming. Note: Power steering works perfectly at all engine RPMs. Plenty of power, even at idle. So I'm not immediately thinking of low hydraulic pressure, since I presume I'd feel that in the steering.
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Last edited by dan1000; 5 Days Ago at 07:52 PM. Reason: Added paragraphs at the end
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  #75  
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Quote:
Originally Posted by dan1000 View Post
Data collected earlier today

Wide open throttle, fan override switch "on", engine fairly cool: Fan measured at 971 RPM.

This post opines that the fan RPM should be around 1300.
971 is NOT GOOD. That is significantly low. Could be, in no particular order:

1) plugged high pressure filter
2) bad motor
3) bad pump
4) sticky/incorrectly adjusted 12v bypass valve

If you've done the filter recently I wouldn't worry about it right now. You need to get a hydraulic pressure gauge screwed into the 12v valve, there are convenient pipe threaded ports for just that. WOT, fan on, measure pressure. If it's low (it is) remove the cap on the adjustment screw and mess around with that and see if the pressure responds to adjustments. I believe this should be 2400 psi at max engine RPM. You need to do this if you replace the motor or pump anyways (nobody does).
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  #76  
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I'm beginning to suspect that the pressure relief valve in the hydraulic fan system is maladjusted, or malperforming. Note: Power steering works perfectly at all engine RPMs. Plenty of power, even at idle. So I'm not immediately thinking of low hydraulic pressure, since I presume I'd feel that in the steering.
You probably wouldn't feel it in the steering because the pump has a priority flow thing on it so the steering gets flow before the fan. If the pump is only putting out half as much as it should the power steering gets plenty for normal operation.
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  #77  
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dan1000 dan1000 is offline
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Thank you, Andy. That gives me somewhere to start. Well, I probably have to start at Harbor Freight or NAPA, since this is a new realm for me -- I'm a software engineer for crying' out loud

Reminds me of the difference between a software engineer and a real engineer. A real engineer washes hands *before* going to the restroom.

Dan
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  #78  
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Originally Posted by dan1000 View Post
Thank you, Andy. That gives me somewhere to start. Well, I probably have to start at Harbor Freight or NAPA, since this is a new realm for me -- I'm a software engineer for crying' out loud

Reminds me of the difference between a software engineer and a real engineer. A real engineer washes hands *before* going to the restroom.

Dan
I wasn't a code monkey, but I worked in IT for a long time. I have confidence
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  #79  
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dan1000 dan1000 is offline
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It takes confidence to buy a vintage motorhome, that's for sure
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  #80  
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CaptPegLeg CaptPegLeg is offline
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I think you should have a two stage pump, one with 3-5 gpm flow that serves the power steering and the other with maybe 12-15 gpm flow to serve the radiator. I could be off on the numbers since I'm trying to use memory which for me is seldom very accurate but you get the idea. it does sound like you need more turns on your fan. Have you checked for leaks on the hydraulic system, specifically the part going from the pump on the 8-92 to the motor attached to the radiator fan?
Like badandy said check hoses, filters first, pump and motor seals. Then bypass valve, they are inexpensive from my experience. That high pressure filter is tucked up under in hard to get spot that make folks tend to forget it but folks with or without one always have new looking oil from what I've read so I would be surprised if that was the problem.
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