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Author Topic: V730/731 overheating engine?  (Read 1325 times)
Chris 85 RTS
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« on: June 15, 2006, 12:00:14 PM »

We are having this discussion on the RTS board, but since other bus makes use the V730/731 trannsmission, I wanted to hear some other experiences. 

Basically my RTS slowly overheats when driven 55+ for long periods of time.  (Note:  Max speed is 63mph)  In addition to the normal concerns about the cooling system, it has been mentioned that there has been some experience with the 2nd gear band dragging in the V730/731 at top RPMs due to a pressure bleed in the valve body. 

My questions resulting from this are:

1)  Is this a known issue with these model transmissions?  It has been suggested that this is because of the city gearing of the RTS, but also suggested that this is the result of a worn vavle body.  My trans seems to shift fine otherwise.

2)  Is there anyway to prove this is the problem, before guessing and paying for work that I don't need?  Measure the fluid temp into the heat exchanger, or measuring the pressure via a test port under operation, etc??

3)  I've also read where someone removed the coolant to fluid heat exchanger and used an air exchanger.  Since I removed the stock AC system, I have plenty of room on the curb side engine bay to add such a thing if that would help.  Comments?

Thanks for any advice,

Chris
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1985 GMC RTS II 40x96 6V92TA MUI V731 IFS
TomC
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« Reply #1 on: June 15, 2006, 05:28:07 PM »

Chris- this sounds more like a radiator problem.  If you go down a hill does the engine cool down?  Since transits are made for stop and go, they have all that idling time to cool down.  Whereas at 55mph, (where you're turning around 2,000rpm) you're working the engine all the time pushing your rounded brick down the road.  What about climbing a steep hill in second-does it also heat up then?  Perhaps second gear is dragging-I don't have an answer for that.

As to the cooler.  First, I'd of course check you're main radiator for blockage and also the shell cooler for blockage also.  Unless you've changed the injectors, the cooling system was well balanced from the factory.  If you do want to do anything with the trans cooler, install a Hayden transcooler (biggest one that'll fit) with thermostatically operated electric fans.  But leave the radiator coolant cooled shell cooler.  What you do is to have the oil line coming out of the transmission (the hot line) first go through the air to oil Hayden cooler then back to the shell cooler back to the transmission.  What this does is to take the majority of stress off the shell cooler and you radiator, but allows the transmission to warm up with the engine and stay at the engine temp (it is just as bad to have a too cool running transmission).  But bottom line, I'd have the trans checked if you think it is dragging and also check the radiator.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Sammy
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« Reply #2 on: June 15, 2006, 06:59:46 PM »

Chris, what type of drive do you have for your radiator cooling fan?
2 most common were: a fan torus or a belt driven fan.
The 730 is mechanically controlled trans and the 731 is an ATEC system - electronically controlled trans.
I agree with Tom, check the operation and efficiency of the cooling system first.
Good luck with your troubleshooting, send an e-mail if you need more help.
Sammy
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Chris 85 RTS
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« Reply #3 on: June 15, 2006, 10:15:18 PM »

Tom, unfortunately I live in FL so there are no hills to speak of with a reasonable distance to test that theory, but that's a good idea.

Belt driven fan.  It has been suggested also that at top governed speed the fan actually spins too fast loosing efficiency.
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1985 GMC RTS II 40x96 6V92TA MUI V731 IFS
TomC
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« Reply #4 on: June 15, 2006, 10:37:18 PM »

I too had a belt driven fan originally on my transit setup.  But I had it changed over to direct gear drive (unlike the Hydrostatic drives that engages more as the temp goes up-although my setup does eat more horsepower [say fuel?]).  The main reason was that the belt drive can slip at high speed, unless the belts are very tight.  Then, according to the mechanic, to change the belts you had to take the fan off the hub since the belts were to short to loop through the fan.  Even though I'm sure the fan takes some horsepower to run, I'm glad I did the switch over since it has been zero problems and now have no belts on the engine (the only two belts on the bus are one on the generator and the other on the remote radiator electric fan drive).  The nice thing about the gear drive is that the fan runs opposite of the engine. And since the engine is already running left handed, or opposite of normal engines, the fan is running at right handed rotation so a regular fan was used.  In my case a 30" 8 bladed solid aluminum fan, that is surprisingly quieter than you'd expect.  Unlike the 6 bladed jobs on the RTS's that definitely put out a humming sound.  But, just so long as it works.  Highly recommend changing to gear driven fan, especially if you're going to keep the bus for a few years.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Chris 85 RTS
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« Reply #5 on: June 16, 2006, 05:42:38 AM »

Tom, where did you get the parts for the gear drive, never heard of this before.
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1985 GMC RTS II 40x96 6V92TA MUI V731 IFS
TomC
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« Reply #6 on: June 16, 2006, 07:52:15 AM »

I thought the vast majority of RTS's had the gear driven fan.  I don't know where the mechanic got the gear drive.  But the gear drive has to be made for your specific bus since the offset for the fan in comparison to your fan position has to be exactly right.  While mine works for my bus, it wouldn't work for yours since my AMGeneral has a very different engine positioning than the RTS (coming from originally being a T drive with Flyer in Canada.  But AMGeneral insisted on the V drive, so my engine compartment is very spacious in comparison to any of the GM buses).  You might try bone yards.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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