Prevost 8V71 with water under rocker covers

[lostagain]

My friend Brian from near Trail, BC and I just got home from a trip to Las Vegas and Laughlin, NV. He is running a '85 Prevost XL with 8V71 stock OEM setup. That is the bus he bought this winter from a mutual friend that sadly died 8 years ago. The bus has been sitting all that time until the estate just got settle and the widow sold it to Brian. He had some overheating and loss of coolant problems on the way down and back. We thought it was the rad cap that was letting the coolant run out when hot. The dip stick was always black, no sign of water in the oil. We split up at Hawthorne, NV where he went North and I went NE as I had to be in Butte, MT 2 nights later. He put on a 10psi cap and then the problems got worse. He tells me he was loosing power, the idle would not go below 1500 rpm, and the Jakes seem to stay on most of the time. (He is new to buses and Detroits). He stopped at the DD dealer in Spokane, WA. They said they would pull the engine and do a complete overhaul for $20000, maybe more, ha, ha! They found the fast idle plunger full of oil explaining the 1500rpm idle. They also found the heads have water in them under the covers: milky oil. The dip stick still showing black oil, no water down there. They didn't look into the Jakes as it was late afternoon. He didn't go for the rebuild at the dealer's and drove it home. I am telling him the heads will have to come off to see what's what. And we'll just have to fix what's broken. Meanwhile I thought I would post it here to see what some of you good mechanics think of it. Is there other things that he and I could look at before pulling the heads? I don't know when I will be able to go there (200 miles away), but I can give him advice and encouragement on the phone. Thanks as always.

JC

[luvrbus]

I thought it may have been a head problem blowing the water out in the book Prevost calls for a 3 lb cap guess the 10 lb didn't work out call me if he needs heads I have plenty all it cost is the shipping which maybe more than he buy a set in BC for. Setting so long it could be the injector tube removing the heads is the easiest way to replace those,the water and oil mixed will cause the Jakes to act stupid.Check the compression rings if they are stuck it may need to come all the way down 

A good 6v92 may be a good option for him if you can find the right deal 


good luck   

[lostagain]

Thanks Clifford, I'll tell him that.

J C

[Purplewillie]

Im only 2 hrs north, if he needs an extra pair of hands
Mark

Sent from my SGH-I337M using Tapatalk

[chessie4905]

   From my experience working with 4.3, 5.7. 6.2, and 6.5 diesels, that was either cracked head/s and or headgaskets. They didn't have injector tubes that could leak. Didn't hurt bearings, but changed oil and filters after repairs.

[wg4t50]

Both the 71 & 92 series have injector tubes,  sure sad events but clearly there is an issue not due to a 10 psi cap,  the cap will force more leaking vs an open system.  Sure hope they can solve the issues.
Dave M

[luvrbus]

All a pressure cap does is raise the boiling point of the coolant with other problems it does make it worse when you increase the pressure ,larger radiators usually are low pressure Prevost just calls for a 3 lb cap must there must be something it the system to use s 3 lb cap maybe the HVAC

[wg4t50]

Interesting, never saw a radiator pressure cap less than 7 psi, lots of caps with no pressure on old equipment, so guess I have lead a protected life as a mechanic.
Dave M

[luvrbus]

Even the older buses with a surge tank had a relief valve not a cap per say that were set 4 to 7 lbs

[Don Fairchild]

The Detroit book calls for a 7lb cap and if you take the craftsman guild test 7lbs is the correct answer for the test.

J.C. if were mine I would now pull the heads as Clifford has said, I would also drop the pan and oil cooler. Wash out the engine install new rod and main bearings rebuild the regulator and relief valves put in new oil cooler cores and rebuild the heads, put in fresh injectors and run it. Being it is a 1985 that should be an 8V71TA also rebuild the blower/Gov. assay maybe even change the turbo to a newer one depending what is on it now.

Whish him luck.

Don

[luvrbus]

The way surge tanks are design the water does not circulate through the tank they do get warm and expand Eagles have a 5 lb relief valve on the tank fwiw My 92 book calls for 9 lbs min on highway truck engines pressure is needed to keep the hoses from clasping  

Pressure will not help with the cooling you can have a 20lb cap it is to contain the coolant and raise the boiling point you have one running hot it still runs hot no matter what cap is used the coolant just stays around for a longer period of time, sometimes  

[lostagain]

Thanks again everybody. I'll pass this on to him. We'll see what he wants to do. To be clear Don F.: the 8V71 in his bus is not a turbo engine, it is a natural with the 6 speed manual. I agree that to do it right and fix it properly and have a reliable engine, it should be taken apart and gone over good. A repower is also an option, with a 8V71, or a 8V71TA, or a 6 or 8V92, or a 4 stroke. There is a lot of room in the engine compartment. He has to settle down a bit and study his options.

JC

[luvrbus]

20+ grand will get your attention and leave one speechless for sure to do one right it will cost you 800 bucks a hole just for the parts and machine work nowadays 

[lostagain]

It is possible the deceased PO had the problem before the bus was parked, because there were several jugs of antifreeze and water in the baggage bays. Like Clifford said, water is likely leaking up into one of the heads from a bad injector tube. The extra pressure with the 10psi cap would be pushing more water and fouling the Jakes on that side and making them stay on, explaining the loss of power. What I don't understand is if the oil is milky with water in the heads, why is the dip stick still black? One would think the milky oil would be all over the engine? I talked to Brian last night on the phone. He hasn't looked at it yet. It will be later.

JC

[Timkar]

I may be out in "left field" but first thing I would do is drop the pan, remove valve covers and pressurize the cooling system to check for leaks....