Is my water pump broken??

[thomasinnv]

I think i may need a water pump for my 8v71.  Was running great not getting hot or anything.  I was coming down a grade and I noticed that the temp gauge was higher than it should be considering I was just coasting down hill.  It kept going up even though I was not giving any fuel.  I pulled over and checked the coolant level and all hoses, blower belt etc.  every thing look normal.  when I pulled over the temp quickly went down below normal(about 150, normally always runs @180).  when I took off again the temp went from about 150 to just under 200 in about 30 seconds.  I thought " ok, stuck thermostat or bad water pump"  All I could do was about 40.  any faster and the temp would go way up quick.  even at 40mph the temp fluxuated all over the place.  from 150 to almost 200, and it moved quickly.  I then turned on the heater up front at the driver area and it blew ice cold, just earlier in the day it was blowing warm so I know I didn't forget to open a valve or anything.  Oh yeah, and when i first noticed it warmer than usual i turned on the radiator misters and they had no effect.  it appears to me that there is not an airflow problem, but a water flow problem.  And yes, I did verify the temps with the mechanical gauge on the engine so I know it is not just a gauge going bad.  Seems to me that maybe the water pump is not circulating water, especially since there is no hot water up front.  what say you all?  am I looking in the right direction?  If it is a pump, anyone have one laying around they could part with?  I seem to remember they being very expensive?  suggestions??

[luvrbus]

Derrick about the only thing that will cause the water pump not circulate is a sheared key or your hose has collapsed at the bottom rebuild kits are around 190 bucks for one with a new shaft and impeller seals only about 1/2 of that


good luck

[buswarrior]

Hold on, how do we know the gauge or sender hasn't joined an obscure religious movement?

Did you see the mechanical gauge read hot and cold too?


well, if the drive on the pump is broken, why would we still be getting sporadic cooling?

I'm suspicious of the coolant level and/or air someplace.

How this has suddenly happened is beyond me?

How did you decide the coolant level is ok?

Any recent work or added coolant?

happy coaching!
buswarrior

[hargreaves]

The water pump has an  impeller that  is held tightly to the tapered shaft with a lock nut. If the impeller starts to slip, which happens from time to time, you will not get enough coolant movement in the system. At idle there is probably enough movement to keep it cool, but when you start to speed up the impeller slips.

It is relatively easy to check, just unbolt the cover after you drain the coolant , and see if you can spin the impeller, if you can, change it. on the back side of the impeller is a ceramic seal, the new impeller should come with one.

[thomasinnv]

Hold on, how do we know the gauge or sender hasn't joined an obscure religious movement?

Did you see the mechanical gauge read hot and cold too?

yes I did witness the mechanical gauge read hot and cold in unison with the electronic gauge

well, if the drive on the pump is broken, why would we still be getting sporadic cooling?

I was thinking more of a loose impeller behaving  like hargreaves has suggested

I'm suspicious of the coolant level and/or air someplace.

I confirmed the coolant level was up to the correct level by the sight glass on the tank.  If air had made it's way into the system it would have either gotten in through a leak somewhere which would be obvious by low coolant level or coolant running out of the bus somewhere, or it would have to be introduced by cylinder compression through a crack or blown gasket somewhere which would most likely also be evident by the coolant being under high pressure and blowing out the pressure relief.

How this has suddenly happened is beyond me?

my guess would again be what hargreaves stated...the impeller nut has finally just loosened enough that the impeller no longer has a 'grip' on the shaft

How did you decide the coolant level is ok?

the sight glass in the reserve tank AND the fluid level check light

Any recent work or added coolant?

nothing at all.  I made 200 miles of my trip today without indecent before this problem suddenly arose, including a few 6% uphill grades without ever getting hot.

not to dispute anything, this is all purely speculation on my part.  just seems to make sense to me but there are many more knowledgeable folks on here than myself.

BW, I assume that by striking out some of your questions that you have answered them yourself.  I chose to go ahead and answer them anyway in case they may be of some help to someone else reading

hargreaves...I assume by your instructions that the impeller can be changed without removing the whole pump assembly?  seems like a pretty straight forward repair?

[artvonne]

  My first guess is T-stat. They can suddenly fail and become erratic. Second, as suggested earlier, is a hose collapsing (or getting an embelism (internal rupture between layers that filles with cooland and swells blocking off flow)). Third could be a head gasket, but as your coolant level is normal that becomes more doubtful.     But not so fast.

  While I havnt actually seen a Detroit water pump, I know its like any other engine pump. Even if they leak they will still pump. The impeller can wear and reduce flow, but that never creates intermitant flow, it would just gradually slow down the flow. While not impossible, the impellor coming loose and working intermitently seems a stretch. Im concerned about no heat in the front heater. Is it possible you have an air lock? You said you were climbing a grade. If there is any air in the system, air will rise to the highest point. So is it a flow problem, or an air problem? And if its an air problem, you have a leak somewhere, or a blown head gasket. You cant very well have a full coolant tank if there is air in the front heater.

  IIRC there are numerous air bleeds on a Bus. If your lucky you maybe had some rouge air in the system that finally worked itself loose and is causing trouble. Whatever you do, remember these guys here have all said 190F is max on these big old dudes. Not 200F. You sure dont want to crack a head or pop a liner.

 

[thomasinnv]

  My first guess is T-stat. They can suddenly fail and become erratic.

That was my first guess too, but if it was just a t-stat the front heater would still get hot water.  The water being supplied to the heater loop bypasses the t-stats so a t-stat would have no bearing on the temp of the water going to the heaters.

Second, as suggested earlier, is a hose collapsing (or getting an embolism (internal rupture between layers that fills with coolant and swells blocking off flow)).

I suppose that is a possibility, however I would think fairly remote.  At times the coolant temp does come back down to normal indicating an increase in water flow.  when it does there is still no heat at the heater.  The way the coolant system is routed I can't see how a hose collapse could cause an overheat situation and zero heat at the heater at the same time.  there would need to be multiple hose collapses or embolisms.  Of course this is all purely speculation and I don't claim to be any expert.

Third could be a head gasket, but as your coolant level is normal that becomes more doubtful.     But not so fast.

as you said, doubtful.  the symptoms just aren't there for this.

While I haven't actually seen a Detroit water pump, I know its like any other engine pump. Even if they leak they will still pump. The impeller can wear and reduce flow, but that never creates intermittent flow, it would just gradually slow down the flow. While not impossible, the impeller coming loose and working intermittently seems a stretch. I'm concerned about no heat in the front heater. Is it possible you have an air lock? You said you were climbing a grade. If there is any air in the system, air will rise to the highest point. So is it a flow problem, or an air problem? And if its an air problem, you have a leak somewhere, or a blown head gasket. You cant very well have a full coolant tank if there is air in the front heater.

FWIW, the pump is not leaking.  there is no water in the oil or vice verse, and no coolant escaping the pump housing.  As someone mentioned before an impeller coming loose has been known to happen on these engines.  They actually sell a kit to replace the ceramic insert on the impeller and da-book has instructions for the procedure.  That tells me they knew it could happen and not just a fluke.  I had a jeep years ago and the impeller cracked causing it to spin freely on the shaft.  it acted much the same way.  it was maddening trying to find the problem.  i replaced radiator, hoses, t-stat, temp sender and finally ended up being about a $25 part(water pump).

even if there were air in the front heater that would still not account for the engine temp going up above normal.  when the problem showed itself I was not climbing a grade, I was about 10 miles into a down grade with no throttle just coasting.  There is no doubt in my mind that the coolant level is full.  There is a site glass in the tank and I can see the coolant level at the same level it always is.

IIRC there are numerous air bleeds on a Bus. If your lucky you maybe had some rouge air in the system that finally worked itself loose and is causing trouble. Whatever you do, remember these guys here have all said 190F is max on these big old dudes. Not 200F. You sure dont want to crack a head or pop a liner.

I think you may be off a little on your temp suggestions.  While we all know these engines do not like to get hot, 190 is certainly not the max.  many run there all day as normal with no ill effects.  the bus manufacturers put alarm stats on these as a safety against un caring drivers to shut them off before the point of no return.  alarm stats are over 200.  (if memory serves they are 210 and 220, and some adjustable)  while i would certainly not allow it to reach 200, just not worth taking the chance.  remember the v71 series (dry liners) are slightly more tolerant to heating than the 92 series (wet liners).  so I'm told anyway.  if 190 was the max there would be many more buses on the side of the highway "cooling off".  push a loaded conversion with full size toad up an 8% grade and see if you don't reach 190.

[bevans6]

Well, it's not hard although extremely messy to take the water pump off and have a look.  They are quite rebuildable, you probably won't need another one.  It's the 20 odd gallons of coolant that are the problem...

On your bus you may be able to get in as far as you need to without actually taking it off the engine.

Brian

[RickB]

If you have an IR gun shoot the inlet and outlet of the water pump and the inlets and outlets of the t stats too.

[buswarrior]

No lengths of hose long enough to be able to collapse on mine. All metal pipes with short straight sections of hose to connect them.

I like the impeller idea, get out your buckets and have a look-see!

happy coaching!
buswarrior

[luvrbus]

Derrick, the key to drive the impeller is on the drive gear behind the water pump it has to be removed to check the key, keep in mind the water flows through the oil cooler first then up from there just follow the path with a IR gun and you find the spot.
Not much on MCI buses but most buses have a plugs on the pump to check the flow by making a loop of clear plastic pipe


good luck

[artvonne]

 

Third could be a head gasket.

as you said, doubtful.  the symptoms just aren't there for this.

  Not to argue, but you have almost every symptom of a blown head gasket. Oil and coolant swapping is generally only seen the later stages of failure, or in complete failure. I only offered doubt because you said the coolant level is up. But then you said you have no front heat, thats it was cold. Is that because the heater is full of air? If its full of air, how can your level be correct? Have you bled the system of all air and re-checked you level? And if there is air in the system, where did it come from? That should be the first part of your diagnosis IMHO. A slipping pump wouldnt put air in the system unless you overheated past the boiling point and barfed coolant out the overflow.

  For the Detroit gurus out there, I am curious about the pump being able to slip intermitently. How can it only slip under high heat loads but not lower loads? I would think that once the key sheared it would just spin and that would be the end of it. Has this been seen before?? 

[thomasinnv]

OK so I got out the buckets and drained the coolant, and took off the pump cover plate.  It was just as I had expected...The nut had backed off the shaft and the impeller was spinning freely.  I took the nut almost 2 full turns before it started tightening up.  the key seems to be intact as the impeller no longer spun freely when i tightened it up.  The book says that the insert should be replaced any time the impeller is removed for any reason, so I am going to order a new impeller with insert installed.  I am a little concerned about the shaft though, there seems to be a groove worn into the shaft where the washer sits from the washer having spun around from being loose.  Am I ok to leave the shaft as is so long as the groove doesnt interfere with where the insert is supposed to press against the shaft?  or should the shaft be replaced anyway?  I am going to replace the washer and nut too.

artvonne, there was no air into the system.  there was no heat because there was no water being pumped to the heater core.  FWIW, if you have an impeller just sitting loosely on a shaft thats turning 1500 to 2000 rpm that impeller is still going to turn some, however slowly that may be.  it just happened to be enough to flow just enough water to keep it cool under little to no load, but not enough to get any water all the way to the front of the bus for the heater.

[TomC]

Considering the cost of a cracked head or overheating to the point of an engine overhaul, don't fool around.  Replace the water pump and thermostats! Good Luck, TomC

[JohnEd]

What Tom said. 

I am the Cavalier risk taker with my own stuff....sorta.....when I can afford the outcome.  NOT IN THIS CASE.  I would have been sitting alongside the road doing all that manly stuff like whimpering and looking skyward with a "why Me".  Oh, and waiting for the road service wrecker to tow me in and having a Brewskie while relaxed and watching live TV or a DVD or pestering Mama.  Friends don't let friends drive a "hot" DD TU Stroke EVER.  It will always end badly.   At least that is the impression I get.  You got away with murder.  Good for you.

John the risk taker