8V92 Temperature?

[ajhaig]

Since we had our exhaust manifold gasket replaced I've noticed that our motor (8V92) is running about 4-5 degrees warmer then it had before. The temp will peak at about 196 after a long up hill climb. Could this increase be related to the new gasket?

Also, we now have much more power and a cleaner engine compartment!

AJ

[Jerry Winchester]

AJ,

Our old 92 would do the same thing when pulling hard. The more efficient exhaust feeding the turbo should produce rated HP and that will also cause more heat. I had this same issue with a leaking manifold tube that runs from the manifold to the turbo turbine inlet.

I don't know how accurate the gauge is on our new coach, but in the "Gauge Mode", the digital readout says the water temp is always around 200, so go figure.

[Joe Cannarozzi]

AJ the 8V is a pretty cool running engine from what I have learned.

In the flat ours almost gets to 180 but not quite.

196 at the top of a hard grade is probably close to normal.

The newer diesels run a hotter thermostat, 195 t0 205, compared to the old standard 180. The only reason I can figure is for better emissions. Don't care for it, less room for error when a problem does occur. I switched my Cat, that is a 1992, from an original 195 to a 180 about 10 years ago and I believe it has added years to that engine.

On a side note our 8V's have 2 thermostats one for each side and the temp gauge is only monitoring one of them. Fortunately they are designed to fail open not closed.

[Jon Wehrenberg]

AJ,

Joe is on the money with his comments. You are doing exactly the right thing noticing subtle changes in your gauges. Often an imminent problem first appears as a slight change from what is normal in the gauges.

All 8V92 engines and their cooling systems are prone to cooling issues if the correct coolant (antifreeze) is not used or maintained. It is not uncommon for the radiator tubes to become blocked due to lack of maintenance so temperature is a good indicator.

The turbo boost gauge, and the pyrometers also tell a story. If you had a bad gasket you may not have been able to reach full boost and maybe the pyros were different. The 8V92 also has had a history of failed manifold gaskets or cracked manifolds.

The transmission temperature gauge is another good indicator of conditions. That five speed transmission is very robust, and the temps should track the engine temps. But overfilling it even by a little could cause higher trannie temps.

You could end up the 8V92 guru because you are running your coach and putting on the miles, and learning all the way.

[BrianE]

AJ,

Since we had an in-frame overhaul about 8k miles ago, our numbers may be useful comparisons. We do a lot of mountain driving in the west and our climbing coolant temps are identical to yours. We run a little less than 180 on a cool day flat terrain which may say something about the guage accuracy. Since the overhaul we are getting a full 24" of boost on the hills and can maintain high boost for long grades as long as we keep the pyros below 1000F. When starting what we think will be an extended grade, I don't hesitate to open the windows, turn on the dash heater and circ. pump and slow/shift to help maintain coolant temp. Using this method we easily keep the coolant temp below 200 and it's seldom that we can't take an extended grade in 3rd or 4th gear. My next project is to install a straight-through stainless muffler and while I don't expect much in the way of mileage, I am hoping that it will help to maintain pyro temps on the grades. By the way, the more I learn about the old 92 the better I like it. :)

[Jon Wehrenberg]

Brian,

I don't think EGT (pyros) matter. At full throttle and 2100 RPM I could hit 1100. I think they are useful for comparative purposes, and possibly to detect overly rich or plugged injectors, but unlike in our planes I don't think we have a limit. If there is a limit I have never seen it written or discussed anywhere.

And yes an 8V92 is sweet. If only they got better mileage.

[ajhaig]

Thanks everyone... we had a nice ride to Buckhorn Lake Resort in Kerrville, TX today.

Don't mess with Texas!

[BrianE]

Jon,

Agreed. I haven't seen limits either. It has been my experience however that high pyros will see coolant temps following soon after. It's a trend instrument like the rate of climb. :D

[Jon Wehrenberg]

Brian,

When the pyros are high, as in full throttle heavy load conditions such as hill climbing, my experience has been that the temps will rise, but then stabilize.

We have a hill north of us on I 75 that is steep and several miles long. We run it often and in hot and cool months. On both of my coaches I would go to full power and take whatever speed the coach gave me holding my foot to the floor for the duration. I would see 55 to 60 in either coach with the speed neither dropping or climbing. As I recall on the 8V92 my pyros would stabilize almost equal at 1100, the boost gauge would be pegged, and varying a little depending on OAT my coolant would be 195 to 205 where it would stabilize. I used to worry about temps on a 95 degree day, but when I consider that the engine is producing less HP due to the less dense air I realize that Mother Nature has a way to automatically compensate for high OATs.

If I turned off the AC all gauge indications would be the same, but I would pick up a little speed (maybe). I think the outside air temp had more of an impact on performance and gauge readings than anything else, including my techniques.

The transmission differences between the two coaches appear to me to be the biggest factor in how I climbed the hills, with the 5 speed being the better in my opinion because it would not upshift with full throttle until I hit 2100 or so. The 6 speed will do the same, but I have to select either performance mode or manually select a lower gear. The six speed and the rear end gearing on the current coach are OK, but are not optimal for steep hill climbing. I think depending on how an 8V92 with the 5 speed is geared the coach may reach an equilibrium or hunt up and down the gears unless manually shifted.

The only time I saw engine temps exceed the above is when the radiator was gradually plugging, and within a year from when I first noticed the temps climbing I had to have it recored.

[JIM CHALOUPKA]

Jon, is that your current bus that you had recored, or was it the previous one?

It would be interesting to know if your trans. updating has an effect on your gage readings and performance on the hill you speak about above?

[Loc]

The Prevost owner's manual that I had for my 92 XL (91 chassis) had a limit of 1,200 degrees for the pyro's. The manual indicated that normal operating temperature (coolant) for the 8V92 is 180 to 195 degrees. It also stated that the engine is not considered to be overheating until it hits 215 degrees. However, I would have freaked out if the temperature got above 200 degrees given my prior experience with catastrophic engine failure. In the old XL, we could run all day long in the Texas summers with the bus air on and stay just below 195. If we were climbing hills, the bus seemed to stay at or below 195 degrees if I kept the pyros between 900 and 1,000 degrees and turned the bus air off. This required downshifting to keep the rpm's up around 1,800 and didn't make us the faster one to the top of the hill, but we got there.

[BrianE]

Great discussion! LOC, thanks for the input, we've had the same sad experience. That sinking feeling of seeing a huge cloud of steam in the mirror followed by a sudden forced landing made me very sensitive about seeing coolant temp in excess of 200f. Thanks for the manual references also. Sometimes we have to gang up on Jon just a little to keep him honest. :D
JON, I certainly agree that ambient conditions are the main ingredient to engine performance. There are lots of 6% grades in the Sierras and Rockies and we try to climb them in the cool. All in all, I'm feeling the money we've sunk in the '94 has been well spent and will continue with a program of upgrades/preventative mtc. She currently sits with wheels off and shocks, hoses and brake chambers laying on the floor for replacement. One doesn't understand the full significance of polishing the slack adjusters until having to clean them up after 14 years of normal use. Sevierville or bust!

[dalej]

We're proud of you Brian! Keep us posted also some photos.

[Jon Wehrenberg]

I followed the "balls to the wall" method of operating. Since DDEC decides when the temperatures are dangerous, and the internal sensors are likely more accurate than the gauge with numbers and hash marks almost too small to read accurately my only concern is that the temperature needle did not keep moving to the right.

A 6% grade of several miles in 95 degree temps was a thermal challenge, but except for when the radiator was starting to plug, the temperature gauge stopped climbing at some point and as long as it was below the 215 point by some clear margin I was good to go.

The Series 60 runs much hotter as has been discussed, and the same hill will see the coach fan cycle between the low and high settings and the temperature gauge will not stabilize at some high temperature, but will go up or down to match the temperature set points in the computer for the fan clutch which has two speeds.

I think our gauges as small as they are lack the accuracy of digital readouts that have been calibrated, but they are good enough to know if we are approaching trouble with temps or pressures. I only look to insure the gauges are sitting in a "normal" position, normal varying with temperature and other factors, and if they are moving in the wrong direction and not stable.

[Loc]

Jon,

I followed the same operating procedure until I trashed the engine. I figured as well that the DDEC II would properly regulate everything. I had checked the DDEC set up to ensure that all of the temperature and low oil pressure shutdowns were turned "on". When we blew the engine it did not protect itself. I assume that the temperature sensor was encrusted like the radiator and did not properly function. After the unfortunate engine trashing incident, I used a little less of the long pedal on the right and watched the temperatures like a hawk (coolant, pyro and transmission temp). The transmission temp had a significant impact on the degree (pun intended) to which the coolant temp would increase quickly. Gearing down and keeping the rpm's up had a visible impact on the tranny temp. I also had the radiator flushed every 2 years or 50k miles whichever came first.

It is a little different with the Series 60. I am still trying to get used to the normal operating range of the temperature guage. The first couple of times climbing a hill I freaked out because the temp would climb and then drop and then climb again which was not what I was used to with the 8V92. I figure in a couple of years, I will be comfortable with S60.

[Petervs]

Hi LOC

My series 60 coach came with a nice mod from the first owner. He installed two additional idiot lights with dim LEDs in them ( so you can just see them on in the daytime, but not to bright at night. Each one indicates the on or off status of the cooling fan, low and high mode. They are wired to points in the electrical bay under the drivers side window.

So for me it is very easy to see how the engine cooling is behaving. Both lights off, means no fan on at all, when the engine is first started and still warming up. Then the LOW FAN light comes on and stays on for all normal driving. When you climb a hill, the LOW fan stays on, the coolant temp gradually rises from it's thermostat setting of 195 degrees, and when it gets to 200, the HIGH FAN light comes on in addition to the LOW FAN, and you can see the coolant temp begin to drop. On the longest hill on the hottest day I have never seen more than 210 degrees.

He also added a switch that allows me to manually turn on the high fan prior to a big hill, but I have never seen the need to do that.

[Jon Wehrenberg]

Loc,

I never relied solely on the DDEC shutdowns to protect me. I am always looking at my gauges, and the defining moment for me to recore the radiator was a temperature that kept creeping up while climbing a hill.

The coolant sensor in the tank is only intended to function if the coolant drops, not in response to rising temps. That is another sensor.

[Loc]

Jon,

My bad, I meant the high coolant temperature sensor not the low coolant sensor in the surge tank. I didn't rely on the DDEC to protect the bus, but I did make a note that it did not.

[Jon Wehrenberg]

In response to Peter's post, he has a nice set up as he described.

In our buses, unlike trucks we do not have natural flow past the radiator so a fan is critical. In the early coaches there were instances of temperatures getting too high due to the clutch settings. It is my understanding that they are now set at 204 and 208 for the low and high speeds of the fan.

I don't have the lights Peter describes, but I can watch my clutch cycle between the two speeds on the temperature gauge during normal driving. This has been stated previously but for those new to the forum, if you ever have problems with overheating due to a failed clutch there are two metric bolts in the end of the fan drive shaft that can be removed and inserted in two tabs that are on the fan hub to secure the fan to the rotating inner shaft. That in essence locks the fan in the "on" position all the time.

[Kevin Erion]

The fan also turns on low when you turn the Prevost dash air on, does not mater what temp the motor is. Today I spent some time changing my clutch for the fan, along with playing with the Webasco, but we will talk about that later. Not so easy but doable for me, I estimate about 4 hours including cleaning. My old clutch was starting to make a noise like a bearing was going out. I like doing the work at my shop, not on the side of the road. On my old bus I also installed a switch to turn the fan on, towing 17000lbs, you better make sure to turn it on before the hill when its warm outside!

[Just Plain Jeff]

On some older coaches, the fan is a manual operation. You have to watch the temperature, then kick it in. There is also a 'circulating pump' switch as the distribution of coolant to the water heater is optional.

[Jon Wehrenberg]

Tell me more about that manual fan. never saw one of them.

[Joe Cannarozzi]

What about that circulating pump. Are you suggesting the method Brian described he does running the heater on a hard pull happens automatically?

[Just Plain Jeff]

It's tough to make generalizations about some of the early coaches. If you are bored, read the rest of this post.

Prevost had primarly built for the Canadian market with a wide variety of models, lengths and features up until 1968. Most notably, they introduced the Super Panoramique, delivering the first coach to Summerset Bus of New Jersey in March of '68. At that time Prevost also continued to produce the Champion at a 35' length, both for seated coach markets.

As to 'motor homes,' their first entry was in 1951 with a Prevost Car conversion done. There is still one around, owned by Alan Hamer (there are pictures of it over on the Prevost-stuff site in the articles section).

During the 1950's there were several Citadin's around at a 28-ft length. Pretty funky looking critters.

In 1978, the first Mirage was introduced at the FMCA show in Columbus, OH. This was a serious attempt to have an integrated chassis into the M/H marketplace. The features of these coaches change quite a bit.

The oldest 'converted' coach I've personally seen was a 1981 Liberty. Frank Konigseder Sr., had built his first coach out of a 3-million mile Greyhound in his backyard and was looking for a better answer (there had to be a better one!), and landed on the Prevost shell.

For those in the TBC, you may find an XL manual that describes more or less of a standardized shell from 1981-....

The oldest coach I have ever put my hands on is a 1984 Country Coach. The control systems, as Joe indicated were 'manually enabled.' The idea being, I guess, that certain shell features and conversion features were not automatic or sensor driven as these are 12v coaches without any software, manual fuel injection (which did not appear until about 1987, '86 inch wide coaches.)

The standardization of shells really happened when Americans were running Prevost Car. They went to rallies, much as Bill Jensen comes to the POG rallies, to help explain and answer questions, which is a very nice thing for all of us.

One neat feature on the 84 CC that I saw was that it had the ability to enable electrically-driven cooling fans for the generator. Perhaps today's generators run cooler, but on our 96 Liberty, the cooling was passive, with a grate at the bottom of the generator bay (a converter-specific feature).

What put Prevost solidly into the 'motorhome' (camper) market was that the company was going head-to-head with MCI in the late '70's - early '80s. Prevost, with American ownership at that time, offered converters a special business arrangement, which was to provide a shell, with only a deposit, during the conversion period, with payment only when it was completed, to stimulate the sometimes cash-short converters to go with Prevost. It worked, and that practice continues more or less today.

Prevost has a long history of making special models for specific marketplaces. We know about the H5-60, the articulated bus/train; the H3-40, H3-41, H3-45, XL, XLV, XL-II and so on. Recently Prevost delivered some inventoried XL-II 40-footers and will build more if the demand is there.

Long answer to simple question.

But hey, I get up at 0400 every morning and have to something.

[truk4u]

which did not appear until about 1987, '86 inch wide coaches.

Very interesting and informative Sockman, but your loyal followers must point out flaws (rare as they are) when we see them. I think you may have meant 96" inch wide coaches and that was probably about the time they switched to 102".

If I am incorrect, I sincerely apologize and will go back to playing with my toy trucks.:p

[Just Plain Jeff]

Mr. Former Resinmobile man: Thank you for pointing out my 0400 this morning error.

Now you can go back to play with (Message garbled in transmission)

[Darrell McCarley]

Jon, You said that you had your radiator routed. Do you know the best way to flush a radiator without removing it from the bus? What type of flush is best? My 8v92 is beginning to heat up in the western mountains during the summer on I-8 from Eloy, Az to San Diego. My temp gets to 205 and I then pull over to cool down. May be forced to remove the radiator but will wait for your advise. Thanks for the post on manifold gaskets. Replaced my gasket yesterday. Glad you told about anti-freeze when bolt and stud are both removed. I drained the radiator before starting. Replacing the manifold gasket was not as hard as I thought it would be. Thanks

[Jon Wehrenberg]

Darrell, The core of the radiator was blocked as yours is likely to be. The radiator was removed and recored. A big vehicle radiator shop can handle that pretty cheaply. It was too long ago for me to know the specifics, but it was much less than a new radiator. I have never back flushed or used any flushing materials.

The problem is silicone dropout. I changed coolant every two years and the conditioning filters every six months and used only anti freeze meeting the DD specs, but at 10 years of life the problem occurred.

I think Loc had a similar problem. It is common for an 8V92 to have this problem and it reinforces why coolant maintenance is critical.

BTW, hitting 205 would not have alarmed me, but if it did not stop there then I knew the time had come to address the problem.

[Loc]

Darrell,

If you are starting to have temperature issues, I would spend the money to have the radiator pulled and sent to a radiator shop to be rodded. I replaced the radiator on my 92 XL when I blew the engine because of a clogged radiator. I put a new radiator in from Prevost at that time. Two years later (approximately 45,000 miles) I had the radiator flushed and had it inspected. It showed about 15% blockage after two years and I was meticulous on my maintenance of the radiator. I pulled the radiator and had it rodded after two years. If I remember correctly, I spent about $900 to pull it and have it rodded. If you decide only to flush the radiator, remove the bottom hose and visually inspect the inside of the core as best you can. I would do it personally, as I had mine inspected at purchase and the mechanic did not note any issues with the radiator (I blew the engine 2 years later).

Loc

[Joe Cannarozzi]

I am not satisfied with the response to my circulating pump question. JPJ throws out this suggestion about a circulating pump that assists in cooling high engine temps and does not answer sufficiently. That's O/K cause it has urged me to bring up these questions that I have been meaning to get answered.

We have OTR A/C. I have noticed in the top of the OTR heater core/evaporator bay a circulating pump plumbed into the copper antifreeze lines.

It is my assumption that on a car the heater core loop is small enough that the water pump has enough volume to flow water through it sufficiently without the necessity of an additional pump.

I'm also assuming on the bus this is not the case, hence this pump. Or is it?

2123

2124

So, is this pump to circulate water through the main heater core, or to pump it forward to the smaller drivers heater core, or both? Is it 12 or 24 volt. If it fails will we still be able to draw heat off the system or not? Is it there for, as JPJ suggests, specifically to lower engine temps. when necessary?

Also for the older coach owners. Does anyone have this same dash switch as pictured below and what is its purpose? When would it be used? I have never had to use this switch.

2125

[Jon Wehrenberg]

Joe, I forgot to answer that one.

The coolant loop going through the coach on coaches of that vintage got generally acceptable flow rates to provide the necessary heat because of the engine pump.

I suspect because Prevost was from Canada that they were more sensitive to having a coach you could heat so to insure in extreme cold that sufficient amounts of engine coolant made it from the engine to the windshield in particular, and other area a supplemental pump was provided.

On my 87 that pump was mounted low, passenger side, near the engine, and I do not know if our respective converters moved the pump or if Prevost made a design change between your 86 and my 87. In my 87 Liberty installed heat exchangers with fans in numerous places such as under the sofa, under the bath vanity, under the dinette, etc. Those heat exchangers were part of the cooling system and I was of the opinion the small pump would provide additional flow to them as well.

FWIW Prevost sold parts for that pump and I replaced the brushes once. I do not think that pump has anything to do with controlling engine temps except to the extent the heat exchangers throughout the cooling system would reduce the coolant temps to a degree, but there was no way I would use them to cool the engine on a hot day.

[Just Plain Jeff]

Joe:1.* Your coach picture indicates a switch much newer than the one I was referring to!2.* The coach I was referring to does not have OTR air, so the setup would be much different than you are indicating.3.* You are THE MAN about mechanical stuff and I am not going to even attempt to delve into your turf!I saw the switch and mentioned it.* Sorry if it lead you astray!!!

[Joe Cannarozzi]

So this thing kicks on when the blowers go on and goes off with them?

What about the emergency fan switch on my dash?

[Jon Wehrenberg]

You had to manually turn the pump on with the switch that had a little fan logo on it in order for it to work on my 87. I rarely turned it on. It was not automatic.