How to Improve LXi Engine Cooling Performance

[davidbrady]

(11-02-2013 21:47)Arcticdude Wrote:  Threads like this make me really glad my 60 sits up in the air where it's supposed to!!

Now, now, now... I only mentioned the "lowered S60's" cause that's the only one I have experience with. I didn't mean to exclude the Thrown-Mounted S60's in the earlier birds! I'd wager that they could all do with better venting in the engine compartment. If I'm not mistaken the '96 Owners Manual also limits the cooling to 100 deg F.

[davidbrady]

Today I ordered a dual-port manometer from TruTech Tools to measure static pressures in my LXi engine compartment. (Like most of us, I don't need much of an excuse to add to my tool chest)! It'll be interesting to see what 40,000 CFM of air does to our static pressures. That's a lot of air! Stay tuned!

[al perna]

Well I need to share with you all . There is truly something magical about the N.C. Air lol on our climb on I 26 today we never reached 190 degrees , maybe there is something in the arrr ha ha ha well it helped that it was 38 to 48 degrees .

[davidbrady]

I had a chance to do some testing with my LXi yesterday. The static pressures inside the engine compartment with and without the under-radiator shrouding and with the bus stationary are very similar:

Shroud removed; Fan override set to ON:
Engine RPM: 1200, static pressure: 0.40 inch of H2O
Engine RPM: 1600, static pressure: 0.70 inch of H2O

Shroud restored; Fan override set to ON:
Engine RPM: 1600, static pressure: 0.80 in of H2O

I limited the testing to 1600 engine rpm's because that's the highest my engine fast-idle switch would allow. With a helper, I've previously measured my fan speed at an engine rpm of 1862 and it was 1850 rpm's, so at 1600 rpm's I may not be at peak fan speed. Nonetheless, I think it's safe to assume that we're seeing less than an inch of water static pressure in our engine compartments at peak fan speed. A quick glance at the flow rate chart attached to post (9) of this thread shows that a static pressure of 1" H2O will decrease fan CFM by maybe 10%. This eliminates the idea that the shrouding is creating high static pressures.

The increased cooling performance I see is probably a bus motion thing. When in motion there may be a low pressure area develop under the fan. With the bus stationary we don't see a benefit. This makes sense because the increased cooling I've seen causes the fan to cycle less (actually, it doesn't cycle at all on my routine workout trip). IOW's even with the fan "coasting" the air flow is improved. This hints at a low pressure area.

The next test is to put the shrouding back to see if I can recreate the higher run-time temperatures. If I can show that the performance is markedly worse with the shrouding in place then I'll experiment with louvers stamped into the under-radiator shrouding.

[davidbrady]

Today I ran my usual bus exercise route two times. The first time I had the under-radiator shrouding in place and on the second loop I had it removed.

With the shrouding in place running at 65mph and consuming about 200hp the temps ran a fairly steady 193 deg F. Under the same conditions w/o the shrouding the temps ran at 190.
There are a handful of climbs on my route. With the shrouding in place the fan went to full speed 3 times. With the shrouding removed the fan went to full speed once.
The coolant temperatures climb more slowly at higher horsepower loads, they also drop more rapidly at lower horsepower loads, and they hug the tstat open temperature of 190 deg F at loads less than 200hp.

This is about the best I can do w/o logging data and crunching numbers. I chose an average temperature day of 65 deg F, dry, and no wind. I was able to run back to back comparisons on the same 50 mile loop with the same ambient conditions.

It definitely cools better w/o the shrouding. It's an incremental improvement. I don't know if I'll get the same results by cutting louvers into the center shroud piece but I'm going to try!

[Hisham Amaral]

(11-23-2013 19:21)davidbrady Wrote:  Today I ran my usual bus exercise route two times. The first time I had the under-radiator shrouding in place and on the second loop I had it removed.

With the shrouding in place running at 65mph and consuming about 200hp the temps ran a fairly steady 193 deg F. Under the same conditions w/o the shrouding the temps ran at 190.
There are a handful of climbs on my route. With the shrouding in place the fan went to full speed 3 times. With the shrouding removed the fan went to full speed once.
The coolant temperatures climb more slowly at higher horsepower loads, they also drop more rapidly at lower horsepower loads, and they hugged the tstat open temperature of 190 deg F at loads less than 200hp.

This is about the best I can do w/o logging data and crunching numbers. I chose an average temperature day of 65 deg F, dry, and no wind. I was able to run back to back comparisons on the same 50 mile loop with the same ambient conditions.

It definitely cools better w/o the shrouding. It's an incremental improvement. I don't know if I'll get the same results by cutting louvers into the center shroud piece but I'm going to try!

David
Try to run the engine at Idle and see what will be the temps and how long does the cooling fan run. The only reason we used shroud is to disallow re circulation of air into the and around the cooling fan.
I agree that the system will run cooler and fan does not engage as often as it would when there is a shroud. Better airflow path. Be sure you get the engine to temperature before you run the idle test.
Hish

[cmillsap]

David,

Thank you for the time you have spent on this project. It may well prove to be very beneficial to other Wanderlodge owners. If there is one deficiency in an LXi; it is its inability to climb long grades in high ambient at an acceptable speed due to potential overheating. In those situations; our busses should be able to travel at about 15% higher speeds than they are presently able to do, i.e. 45mph should be 52 mph.

I don’t know the coolant temperature level when your fan switches to full rpm. How are you determining when that happens? I think the incremental increase in cooling capacity is probably more than we might think if we really analyze the results of your tests.

First, we should take into consideration that minimum coolant temperature is controlled by the 190* thermostat. Therefore, we will not know the real delta T of the coolant. Secondly, that the rise in coolant temperature was noticeably slower with the shroud off. Hence, the fan only went to full rpm once instead of three times. We could mathematically project that there was a 66% improvement in cooling efficiency. Further, that we get the benefit of that at the exact time we need it the most; which is when driving up long grades. My experience with the two LXi’ I’ve owned is that the cooling system is more than sufficient on level to mild terrain but is lacking on long 5% and 6 % grades in +100*f ambient where high engine horsepower output is necessary.

The only thing I can see that would contribute to engine overheating in an LXi is the lack of sufficient air (cfm) through the radiator. Certainly, the radiator is sized large enough and the 25 gallon coolant capacity is enormous for that bus. I know that BB sized the coolant system to operate efficiently in 100*F ambient but in my estimation, that is not enough; given the hot summer temperature and those long 6% grades found on the interstates nowadays.

Considering the enormous coolant capacity and the size of the radiator, I doubt that some recirculation of air back through the radiator due to the shroud being removed will overheat the engine when idling or running at minimal horsepower output.

C

[Hisham Amaral]

(11-24-2013 00:18)cmillsap Wrote:  David,

Thank you for the time you have spent on this project. It may well prove to be very beneficial to other Wanderlodge owners. If there is one deficiency in an LXi; it is its inability to climb long grades in high ambient at an acceptable speed due to potential overheating. In those situations; our busses should be able to travel at about 15% higher speeds than they are presently able to do, i.e. 45mph should be 52 mph.

I don’t know the coolant temperature level when your fan switches to full rpm. How are you determining when that happens? I think the incremental increase in cooling capacity is probably more than we might think if we really analyze the results of your tests.

First, we should take into consideration that minimum coolant temperature is controlled by the 190* thermostat. Therefore, we will not know the real delta T of the coolant. Secondly, that the rise in coolant temperature was noticeably slower with the shroud off. Hence, the fan only went to full rpm once instead of three times. We could mathematically project that there was a 66% improvement in cooling efficiency. Further, that we get the benefit of that at the exact time we need it the most; which is when driving up long grades. My experience with the two LXi’ I’ve owned is that the cooling system is more than sufficient on level to mild terrain but is lacking on long 5% and 6 % grades in +100*f ambient where high engine horsepower output is necessary.

The only thing I can see that would contribute to engine overheating in an LXi is the lack of sufficient air (cfm) through the radiator. Certainly, the radiator is sized large enough and the 25 gallon coolant capacity is enormous for that bus. I know that BB sized the coolant system to operate efficiently in 100*F ambient but in my estimation, that is not enough; given the hot summer temperature and those long 6% grades found on the interstates nowadays.

Considering the enormous coolant capacity and the size of the radiator, I doubt that some recirculation of air back through the radiator due to the shroud being removed will overheat the engine when idling or running at minimal horsepower output.

C

Chuck
Try setting at the border from Mexico into USA for about 40 min. to 1 hour and you will see temps claim into the 230's on both trans and engine, I was there I sow that temp go up. When the engine is at idle so are the fan speed you may get the fan to higher speed but that speed is not at full speed to take out 45 HP from the engine.
I agree that for highway speeds reducing restrictions is always a plus for the cooling system, but another story at idle condition.

[davidbrady]

(11-23-2013 21:16)Hisham Amaral Wrote:  David
Try to run the engine at Idle and see what will be the temps and how long does the cooling fan run. The only reason we used shroud is to disallow re circulation of air into the and around the cooling fan.
I agree that the system will run cooler and fan does not engage as often as it would when there is a shroud. Better airflow path. Be sure you get the engine to temperature before you run the idle test.
Hish

Thanks Hish, I very much value your experience and input on this. From what I've seen bus manufacturers have taken steps over the years to restrict hot air recirculation (HAR). When I spoke with Youngs Trasportation and Tours (my transit bus operator here in Asheville) they said Prevost used to hang a neoprene curtain down to almost road level to stop HAR. In this thread we spoke about an air cylinder powered louver which could be as simple as a slotted plate in tracks used to cover over the louvers in the lower shrouding. The question on my mind is, "will louvers in the lower-radiator shroud be worth it; will they perform adequately"? And, we'll get to that at in a moment.

[Hisham Amaral]

(11-24-2013 10:26)davidbrady Wrote:  

(11-23-2013 21:16)Hisham Amaral Wrote:  David
Try to run the engine at Idle and see what will be the temps and how long does the cooling fan run. The only reason we used shroud is to disallow re circulation of air into the and around the cooling fan.
I agree that the system will run cooler and fan does not engage as often as it would when there is a shroud. Better airflow path. Be sure you get the engine to temperature before you run the idle test.
Hish

Thanks Hish, I very much value your experience and input on this. From what I've seen bus manufacturers have taken steps over the years to restrict hot air recirculation (HAR). When I spoke with Youngs Trasportation and Tours (my transit bus operator here in Asheville) they said Prevost used to hang a neoprene curtain down to almost road level to stop HAR. In this thread we spoke about an air cylinder powered louver which could be as simple as a slotted plate in tracks used to cover over the louvers in the lower shrouding. The question on my mind is, "will louvers in the lower-radiator shroud be worth it; will they perform adequately"? And, we'll get to that at in a moment.

David
I would think that would work if the neoprene is flexible to allow the flow when positive pressure is applied to close and open at specific condition, such as at idle the slots close and at road speed open. I don't think you need an air cylinder to do the job in this case, air pressure will do the job.
Use multiple 3"X4" openings and attach a rubber flap to the bottom that can be forced to open at road condition and vacuum from the fan would close the flap.
Hish