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Old 06-15-2021, 06:26 PM   #1
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Overheating issues

Have a 96 Monaco Dynasty 36. has the 8.3L 300hp Cummins engine with an allison 6 speed. 139K miles currently. side mount radiator



have had rv for a little over a year. we use the rv to pull trailer with race car.

all last season pulling across midwest normal operating temps on the old style gauges I would say ran around 185* on water side and probably 160-175ish on the trans temp side.


2 weeks ago we were up north in South Dakota making run after races back down into Iowa. temp climbed as I smelled coolant from drivers seat. hit the shoulder opened back hatch to see water spilling out top of engine where thermostat housing is. This was about 2am in morning so thankfully trailer full of tools with race car. I let the thing cool down for a good 30 mins before starting to diagnose.



Thermostat housing was where coolant leak was and noticed 2 of the 4 bolts holding it all together were loose. my thought process was bolts are now loose due to blowing gaskets out on housing assembly. 2nd thought likely thermostat messed up causing increase in temp pushing out gasket.


learned it has 2 thermostats in housing. pulled both. used some handy gasket maker and bolted back together. filled with water only as I wasn't sure if coolant specific required at time.


got back on road to next race track about 1 hour away. temp ran roughly 180-200 rest of way there. left out for the 7 hour drive home the next night after races. again 180-200 on water temp during the night. normally I run 75mph down highways with trailer. had to back down to 60-64 mph whole way home to stay under 210 temps during day as we didn't make full 7 hour drive at night before pulling off for sleep.


so back home. get 2 new thermostats. put in rv and take for a test drive without trailer down highway. drove 10 miles to town and returned another 10 miles. rv seemed sluggish to me without trailer. still pulled boost levels but temp climbed up over 190 mark which never used to get much over 185 with a trailer.


so here is a list of things done since new thermostats installed.


dropped radiator and CAC. washed both out separately at house with power washer as I do race car radiator. could say it was well overdue needing done as the black grime coming out of radiator was amazing. couple hours later of washing and cleaning I installed radiator and assembly back in.
new peak brand fleetcharge coolant.
new coolant filter.
new air filter.
pulled and checked water pump over.
made sure fan on radiator does turn when engine running.

all new fluid for power steering and fan
with engine running cracked fuel lines 1 at a time at injector to make sure fuel present and listen for engine idle change(Checking firing of injector)
pulled turbo of engine to confirm fan blades inside still good and no play in bearings.
also double checked pacbrake valve was open.
engine running sprayed brakes part cleaner on all hoses and rubber boots to check for air leaks and sucking air.


after all this was done engine still at 68mph cruise speed down highway without trailer now has engine climbing up to around 200* temp maybe touch more. hard to say as gauge doesn't break down in increments to confirm exact temp. just know that normal operation was much lower on gauge.


any ideas?
my thoughts could be fan speed? if it has a 2 speed fan I don't know test procedure to confirm low/high speed operation.
Injection pump wearing out and not enough fuel getting through injectors at speed? again testing procedure I don't know.


time to take it to a shop?
Trade in for a newer unit and save the money on repairs and use for down payment on newer and higher hp unit?
already a good $600-800 in fluids and filters thus far. hate to keep throwing money at it when I have been unsuccessful.
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Old 06-15-2021, 06:43 PM   #2
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you didn't say if you did a coolant flush of the inside of the radiator and the engine.. Or maybe I didn't quite understand. My 330 ISC was running hotter than normal last year and I took it to a local shop and they did the coolant flush and new red coolant....The temps went back to normal.. drove it yesterday from Kansas for 3.5 hrs and it was 96 degrees out..
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Old 06-15-2021, 06:47 PM   #3
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sorry got to rambling on.

yes flushed engine and radiator while it was out getting washed and cleaned with power washer. went back together with new fleetguard coolant.
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Old 06-15-2021, 07:14 PM   #4
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The new style Cummins water pump has a much larger impeller.There are side by side pictures here in one of the Cummins threads.
My guess is you now have an air bubble in your cooling system. BTW Did you replace the pressure cap?
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Old 06-15-2021, 07:27 PM   #5
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Sounds like you've about covered all the bases.
Definitely upgrade the water pump, better circulation and cheap.
Cooling fan really isn't a factor at 68mph on a side radiator model.
Double check the temp ratings on the new thermostats.
Dash gauges are notoriously inaccurate, install a temporary mechanical gauge to make sure you're not chasing your tail.
Good Luck...
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Old 06-15-2021, 08:22 PM   #6
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Temp rating of thermostats are 181* pulled part number off old thermostats and are same.
Have not put a new pressure cap on top of fill tank. Cheap enough to try.

How is best way to check/bleed air bubble out of system. I "think" there isn't an issue as there is coolant circulating but then again thinking gets me in trouble.

Pump looks to have been replaced recently but will possibly just replace it as well.
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Old 06-15-2021, 08:24 PM   #7
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Also gaugea indo believe are accurate as I haven't had issues until recently when I know it overheated with fluid coming out around thermostats.

Also put infrared temp reader on coolant lines going in engine and exiting after thermostats at idle. It matches within 5* of dash reading and gauges at engine compartment as well.
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Old 06-15-2021, 08:25 PM   #8
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At higher temp the hyd. fan is supposed to kick to full speed. If there's an issue /failsafe is supposed to go full speed. Most complaints are full bore fan speed making dust storm and wasting power. That doesn't mean it can't have an issue not speeding up .
Full speed fan as described is pretty intense you should be able to tell if it hitting it. I'm not sure if triggered by ECM setting or temp switch.
At loss of power always try fuel filters. It's not unheard of for two or more unrelated problems to just pop up at the same time. I don't think your motor will go into limp mode without the warning or stop engine light.
If you coolant tank and small return lines to it , are like mine ,you shouldn't get air lock in the motor.
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Old 06-15-2021, 08:31 PM   #9
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Quote:
Originally Posted by Ray,IN View Post
The new style Cummins water pump has a much larger impeller.There are side by side pictures here in one of the Cummins threads.
My guess is you now have an air bubble in your cooling system. BTW Did you replace the pressure cap?
Agree with Ray here, I did a coolant flush and fill, and its not hard to get an air pocket in the system and it can be hard to get it out. Try running it up to temp a time or two in the driveway with the radiator cap off. Use cruise control to hold RPM's Replace the cap if you have not done that but there are only so many reasons why it would hold a higher temp due to failures.
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Old 06-15-2021, 08:54 PM   #10
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Well it isn't stuck in high speed then. Fan speed seems normal from sound and dust movement at idle.

Tank has many smaller 3/8 lines running around to parts of engine and radiator.

Guess I will need to get it in a shop. It's been reliable so hate to part with it unless able to upgrade to a rv with slides and more hp. Would think 100hp increase would be noticeable down highway and up hill pulls with trailer.

B
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Old 06-15-2021, 08:55 PM   #11
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Well it isn't stuck in high speed then. Fan speed seems normal from sound and dust movement at idle.

Tank has many smaller 3/8 lines running around to parts of engine and radiator.

Guess I will need to get it in a shop. It's been reliable so hate to part with it unless able to upgrade to a rv with slides and more hp. Would think 100hp increase would be noticeable down highway and up hill pulls with trailer.

B
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Old 06-15-2021, 08:55 PM   #12
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Is your turbo water cooled? If so it can pump extremely hot exhaust gases into the cooling system. Collapsed cooling hose at speed. Head gasket . Water pump.
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Old 06-15-2021, 08:57 PM   #13
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Quote:
Originally Posted by ftodaro View Post
Agree with Ray here, I did a coolant flush and fill, and its not hard to get an air pocket in the system and it can be hard to get it out. Try running it up to temp a time or two in the driveway with the radiator cap off. Use cruise control to hold RPM's Replace the cap if you have not done that but there are only so many reasons why it would hold a higher temp due to failures.
Down highway when temp climbs over 200 at 68mph. I can let off gas and coast. Within 1/4 of coasting temp will drop back to a normal 185ish. Jump.back into throttle and get to 68mph and watch temp slowly start creeping back up to 200ish.
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Old 06-15-2021, 08:59 PM   #14
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Is your turbo water cooled? If so it can pump extremely hot exhaust gases into the cooling system. Collapsed cooling hose at speed. Head gasket . Water pump.
When I took turbo off to examine only had a small oil line feeding into it on topside. With a large hose dumping back into oil pan off bottom side.
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