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Anyone attempt to connect radiators in series?

radiator cooling fan

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#1 tinkerinWstuff

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Posted 22 February 2012 - 11:11 AM

Looking at the radiator configuration for the 5th gen (assuming 6th is the same), the radiators are essentially a parallel circuit. Water flows into the top of both, or either, radiator and then out the bottom and back to the motor.

So essentially, when the bike is hot and the fan is running, all the water in circulation isn't even passing through the left radiator and the fan. I have to believe that Honda had their reasons for this configuration but curiosity is getting the best of me. Maybe the radiators are too thin and can't handle the full volume of flow?

It would be interesting to remove the upper cross-over tube, route the lower hose from the bottom of the right radiator to the top of the left. Then plug that remaining port at the bottom that was used by the lower cross-over tube.

Thus, all the water would be forced to pass through both radiators in series. I have read lots of discussion about the VTR fan mod for cooling but never a peep about radiators.

#2 FSAE

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Posted 22 February 2012 - 01:40 PM

It's kind of analogous to an electrical circuit; it has to do with resistance. Two parallel resistances are a lot less work for your water pump than two in series. Another factor is the effectiveness of the radiator, which the ratio of the actual heat transfer rate to the maximum possible theoretical rate. Your inlet conditions (ie, temperature) play a large part in the effectiveness since you're comparing inlet to outlet temperatures. I'm pretty sure (without doing the math) that two parallel rads are more "effective" than two in series.

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#3 tinkerinWstuff

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Posted 23 February 2012 - 11:26 PM

I have no doubt that a parallel system is efficient when the bike is moving along with some airflow.

But moving in slow traffic with reduced air flow thru the radiators would seem that a series system would work better.

#4 kaldek

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Posted 24 February 2012 - 01:11 AM

I have no doubt that a parallel system is efficient when the bike is moving along with some airflow.

But moving in slow traffic with reduced air flow thru the radiators would seem that a series system would work better.


Honestly, this argument has been done to death in various forms. People spinning their fans backwards because "it's better than the Honda design" went on, and on, and on.
Have you seen the cooling fan on a CBR1000RR? It's about one-eighth the size of the radiator, in the upper right corner. That's it - and it works.

Our bikes have two radiators, and the fan is basically the same size as the entire left-side unit. It's fine, it works, and I've seen it keep my bike at 231F when the ambient air temperature was 116F! This was in traffic, too.

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#5 tinkerinWstuff

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Posted 24 February 2012 - 10:27 PM

Honestly, this argument has been done to death in various forms. People spinning their fans backwards because "it's better than the Honda design" went on, and on, and on.


So how about a link then? As I said in my OP, I've read plenty on the fan mod but have never seen a discussion on routing the hoses differently.

#6 Kel

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Posted 25 February 2012 - 12:30 AM

My R has 2 radiators and I'm pretty sure they're in series.

#7 kaldek

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Posted 25 February 2012 - 04:06 AM


Honestly, this argument has been done to death in various forms. People spinning their fans backwards because "it's better than the Honda design" went on, and on, and on.


So how about a link then? As I said in my OP, I've read plenty on the fan mod but have never seen a discussion on routing the hoses differently.


Sorry I meant the "spin your fan backwards" thread.

http://www.vfrdiscus...6th-generation/

http://www.vfrdiscus...e__hl__radiator

Basically lots of folks saying the stock design is flawed, yada yada. But, has anyone heard of a VFR overheating and warping the heads? I've been on the forum here for ten years and I don't recall a single one.

My opinion is that the stock design works best when the bike is stationary or moving slowly. If you flip the fan, it will work WORSE when the bike is stationary because it's pulling already-hot air from the engine rather than cooler air from the outside. Someone at Honda ran the numbers on this and they were obviously right, because no VFRs have yet overheated and blown head gaskets or warped heads. In this case, stock works.

As for the running the radiators in series, you may find that the pump hasn't got the balls to move the coolant around and may just cavitate, creating a lot of froth and not much movement of coolant.

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