6v92 overheating question (in an MCI 102c3)

JT4SC · June 08, 2019, 12:38:25 PM

Hello everyone,

I was driving the bus back from LA to San Diego last week when all of a sudden the coolant temp spiked as I was climbing a hill. I immediately pulled over and the temp quickly returned to normal. I was then able to carefully drive the bus another couple miles to my house with some fluctuation in temp coinciding with slight inclines or declines in grades.

Question - what's the most likely culprit? I was thinking water pump but I had the water pump rebuilt approx 4,000 miles ago (although it has been approx 10 years since the rebuild). There is also no coolant leaking from the pump (or anywhere else). My next thought is thermostat, not sure if my symptoms match a thermostat issue?

A clogged radiator would also match these symptoms I believe, but I'm not sure how to tell if that's the issue?

Any insight would be appreciated. I had driven 100+ miles that day with no issues before the sudden spike.

Lin · June 08, 2019, 02:24:46 PM

Unfortunately, with the information given there are many possibilities. I would start with the easiest first. Do the radiators need to be cleaned? Is the fan belt slipping? Are you keeping the rpm's in the right range? Is your air intake in good shape (I once had a heat problem that was caused by the engine air intake hose collapsing under load. It would look fine when the engine was idling though)? Is your temp sensor accurate? etc.

JT4SC · June 08, 2019, 04:26:22 PM

- RPM's = normal

- Fan belt does not appear to be slipping

- temp gauge was just replaced and sender appears to be operating correctly.

What I haven't done is try to clean the radiator itself, I'm going to try that and see what happens. Maybe some road grime is not allowing air to cool the fins?

Utahclaimjumper · June 09, 2019, 08:20:41 AM

Its all about engine loading,, when climbing, speed is not a priority,, drop a gear AS NEEDED to keep the fan speed up and UNLOAD the engine... The heavier the load on the engine the more heat it will make.. Evan if selecting low gear is needed to control heat, it's better than destroying equipment. ( Have you ever wondered why 18 wheelers have so many gears.

?)

Iceni John · June 09, 2019, 08:59:44 AM

A hand-held IR thermometer (yes, I know they're not totally accurate) is useful to check radiator and engine block temperatures. One of several reasons I completely rebuilt my entire cooling system a few years was because my IR thermometer showed that my radiator had a cold spot: the tubes there were blocked by crud in the top tank. I also find a turbo boost gauge to be useful for controlling engine temps - when climbing long grades in hot weather I manually downshift to third on a 3/4 throttle, keep the revs at about 1900 RPM and the boost at about 18 PSI. If I let the boost get higher the temperature will immediately rise, so for my bus that's evidently the sweet spot for climbing.

John

chessie4905 · June 09, 2019, 10:29:34 AM

After you correct the problem, consider a mister system to avoid damage to engine on one of those 100 plus degree days on a grade that seems to last forever.

JT4SC · June 09, 2019, 01:27:47 PM

Thanks for the replies. The bus generally runs on the cooler side, approx 170 or so, which was the case 95% of the way home with many 6% grades. That is until the last hill it had to climb before my house where something gave out. I have an IR thermometer and tomorrow will see if there are any large temp differences and report back.

Follow up question - is flushing the radiator something a novice like myself can tackle, or is this best left to a professional mechanic? If it's something I can tackle with a good youtube video or something I am game to try.

HB of CJ · June 09, 2019, 01:53:31 PM

Respectfully ...

We have not yet determined what constitutes "Normal RPM". Two stroke Detroits MUST be run against the governor going up long steep hills. This means 2000-2200 rpm. Even with partial throttle. Sometimes an automatic will not allow this. The other answers have already covered it. Before anything else check to make sure the radiator(s) is/are full of water.

JT4SC · June 09, 2019, 02:01:44 PM

Quote from: HB of CJ on June 09, 2019, 01:53:31 PM
Respectfully ...

We have not yet determined what constitutes "Normal RPM". Two stroke Detroits MUST be run against the governor going up long steep hills. This means 2000-2200 rpm. Even with partial throttle. Sometimes an automatic will not allow this. The other answers have already covered it. Before anything else check to make sure the radiator(s) is/are full of water.

I should have been more specific - this was not a long steep hill, it was probably around 6% grade and at most 1/2 mile long. The outside temp was in the mid 60's. I went up considerably longer and some steeper hills earlier in the drive with no overheating issues whatsoever.
I am not sure what you mean by "run up against the governor"?

HB of CJ · June 09, 2019, 04:49:09 PM

Running the 2 stroke Detroit Diesel "Against The Governor" means putting your foot to the floor and letting the engine run as fast as it will go. 6v92T Detroits can be governed anywhere from 1800 to 2400 rpm. Running your engine that fast going up a short steep grade will not hurt it.

The older 71 N series Detroits were designed to run against the governor in heavy truck service. Very under powered. I figure the DD 92 series would be about the same except for the big MUI 500 hp 8v92TA which could run at about 1500 going down the road. Hills? Flat out wide open.

Hope this helps. MUI means no computers. Mechanical Unit Injectors. All mechanical. DD means computer controls. N means very old with no turbo charging. Is your Bus Conversion low on radiator water? Other answers pretty much cover what your over heating problem may be.

Respectfully.

luvrbus · June 09, 2019, 04:59:41 PM

Takes very little dirt and grime in the radiators on the C with the 2 side mounted radiators to make it run warm,clean the fins and check the seal around each radiator,they have a habit of collecting dirt at the bottom 4 inches if you cannot see a light through one it is dirty

JT4SC · June 09, 2019, 10:08:00 PM

Thanks guys, I'm going to clean the radiator tomorrow and see if that helps.

As far as the thermostat possibly being the issue - since the temp quickly comes back down to normal when there is not a heavy load on the engine does that make this being a thermostat failure less likely? My understanding is if it's a bad thermostat the temp will climb quickly but generally stays high.

Geoff · June 10, 2019, 07:04:14 AM

I have yet to read what the high temperature "spike" was in degrees.

JT4SC · June 10, 2019, 09:21:00 AM

Quote from: Geoff on June 10, 2019, 07:04:14 AM
I have yet to read what the high temperature "spike" was in degrees.

It was darn close to 240, if not at 240. Close enough for me to immediately pull over on the 15 frwy.

luvrbus · June 10, 2019, 10:17:45 AM

Quote from: JT4SC on June 10, 2019, 09:21:00 AM
It was darn close to 240, if not at 240. Close enough for me to immediately pull over on the 15 frwy.

with the rebuilt water pump whom ever done the rebuild may not have the impeller tight on the shaft and the shaft is spinning but not the impeller happens all the time around here