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Old 10-20-2017, 08:23 AM   #41 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
As long as you may find one (or two) with enough flow, there's no actual reason for a mechanical fan to be better than an electric one.
I recommend you put it to the test. The heavier the load, the worse are electric fans.

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Old 10-20-2017, 01:16 PM   #42 (permalink)
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All the radiator is affected by is temperature and mass rate of flow. The fan determines the rate of flow by blade configuration and RPM.
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Old 10-20-2017, 02:15 PM   #43 (permalink)
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Quote:
Originally Posted by slowmover View Post
There's no "risk" in running 58-62. Big trucks run 62-66. A little above them, but below the idiots in cars is "the rocking chair".

As to towing, you didn't need a Class V hitch. Class IV would have worked.

Towing plus A/C use: HD clutched mechanical fan.

The downside of a straight six is weight. A lot of Iron to keep cool. I wouldn't screw with old school in this. In fact I'd get the radiator, fan shroud and fan from a big block van.

Then you can mess with thermostat temps.

I'd also add a second A/T cooler (plate and fin) downstream from radiator that will bypass cold fluid (B&M Racing). Centered low across rad face, but "within" fan shroud profile and out ahead of all else.
I cropped a lot out for brevity.

The "risk" in running substantially different speed than the flow of traffic is well known and well documented. I'm not going to get into it here other than to say that drafting people is a dramatic reduction in fuel usage...and it's much easier to maintain a good draft distance if you find groups of people going a consistent speed. Around here that speed is 70-80mph.

For the hitch, the Class IV and V hitches were all physically similar in size, and likely would have the same negative effect on FE. Since there was only a $10 difference in price, I just picked the one that looked like it would "tuck in" to the underside the best. I might have picked the wrong one, looking back at other photos. A Class III might be just fine for my application, i.e. towing a trailer with a Miata racer. They are a bit less complex, with less flanges and plate surfaces hanging out there. It probably would have been a better choice. But any hitch hanging down there would still have a pretty bad effect on FE.

I have a Derale 2 speed electric fan, but haven't installed it yet. I had it ready to go, but the replacement radiator side flanges were slightly different than the OEM radiator. So my 0.25" clearance to the water pump ended up as 0.25" interference! At the moment I'm running the OE heatsink-style clutch fan without a shroud. With no towing temps are stable, but it probably would not be good enough to tow 5000lb.

I do plan on replacing the stock A/T cooler with a separate plate & fin one, thanks for the suggestion on the B&M Racing one!
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Old 10-21-2017, 11:29 AM   #44 (permalink)
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Quote:
Originally Posted by Grant-53 View Post
All the radiator is affected by is temperature and mass rate of flow. The fan determines the rate of flow by blade configuration and RPM.
Again, have you tested?

Here's a clue: No one running HD trucks uses electric fans. The FE incentive is there, but the tech isn't.

OP, the fan shroud is huge. Blades should be halfway in/out or more (less to outside) and fan blade tip should be within 1/2-inch of shroud. All air thru shroud, no exception. (Some vehicles used spring-loaded flaps on shroud to relieve highway air pressure).

Same for the front of the various heat exchangers: directed airflow. Close off the top gaps between exchangers, leave bottom open.

Also need an air dam below vehicle ahead of the shroud rear opening. Negative air pressure is idea.

This was all SOP on carb'd HD/Police engines.

A heavy duty thermal fan clutch also. The penalty for using a fan should be of shortest duration.

FE is a lot of hot oil temp (220F nowadays) and "cool" coolant (185-195F). It takes a powerful fan to step in and keep things in check. I have both coolant and oil temp gauges in the KW and it's the latter I rely upon to keep temps reasonable. (I may know to remove winter cover at 41F, but the gauges are quick to hit me if I don't).

So I also recommend an oil temp gauge.

And you're rationalizing your travel speed. The "discrepancy" problem has as much to do with WHAT traffic is slower. I run 10-12,000 miles/month and all over country. It's the traffic volume that's always the problem. Those studies were ATA trying to get split limits changed.

You try my analysis and you'll see. Acceleration and braking events. Lane changes. (Constant rigid rule about spacing as control) Any of these occur, and you're not in the flow. The flow is always below the upper posted limit. That flow is about maximizing steady state travel.

I spoke of the graph where average mph and average mpg can meet; the desire to be timely AND fuel efficient. This is expressed as cents-per-mile fuel cost. On an annual basis (X-miles). One can easily see that overall truck spec is king. Second is climate, then terrain. Driver Motivation is last. Aero mods wont give you a better cpm without understanding speed. Analyze your records.

If one is only passing governed truck traffic (and similar; at about 63-65/mph), one is close. (I'm going to leave out the stupidity of drafting; a single serious accident at those speeds is life-changing).

You should also test emergency stopping distance from 75 and from 62-mph. One can play around with 200' vehicle spacing distance down closer to 100', but it seems you believe "skill" overcomes statistical verities. Nevertheless, what's the difference in those two? As even today's more sophisticated pickups can't handle a slalom course faster than 57-mph while empty, I urge you to know the time/distance to get down to 55-mph or less.

(You want to disagree with me, fine, then post those stopping distances first, please. A deserted commercial district with wide lanes on a Sunday morning is the perfect place for that).

Slowing is easy. Stopping is hard.

Let tested numbers work for you. Quantify the risk.

Again, I'm really impressed with all the hard work, and consider myself part of your cheering section.

.
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2004.0 DODGE Ram QC/LB 2500 2WD/NV-5600 305/555 ISB. 7,940-lb. Stock. 200,000 miles/5000-hrs @ 40-mph average.
1990 35' Silver Streak TT 7,900-lb.
8-cpm solo & 11-cpm towing; 21-mpg average past 54k-miles
Sold: 1983 Silver Streak 3411

Last edited by slowmover; 10-21-2017 at 11:39 AM..
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Old 10-22-2017, 01:35 PM   #45 (permalink)
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I'm not rationalizing my travel speed. In my OP I said I have a schedule to meet. So I meet that schedule, which requires me to drive pretty much at or above the posted 70mph speed limit. I'm just trying to get better than the 12mpg that I started with. I have the time and ability to mess around with aerodynamics on this $500 van, but not the $30k to buy a Mercedes Sprinter diesel.

In my experiments I found that (at the time with the mods at the time) I got about 15.4mpg at 60mph, and 14.7mpg at 70-80mph. I'm fairly certain (without hard data) that the relatively low delta in FE of 5% has a lot to do with being "in the pack" at 75mph. FWIW I give 2-3x the draft clearance of most drivers here, enough so that there are always people changing lanes into my clearance gap. Even with the suspension and tire upgrades I've done, I know that van is heavy and not Miata-agile.

Regarding the fans, even with the mechanical fan and no shroud the engine coolant never goes above 200F. The radiator inlet temp is about 185F in worst case, while sitting in traffic with the A/C on full blast. Most of the time on the highway the inlet temp is around 150F with engine temp around 180-190F. I'm saying this based on best estimates of engine heater core temps checked on various points of what each letter in "NORMAL" means. Before I try anything else I'll install a real temperature gauge for the engine temp, radiator temp. Thanks for the suggestion on the oil temp, I hadn't considered that before.

For towing I should probably put a temp gauge on the A/T fluid too, though with a decent cooler it's unlikely to go too high. The Ford racer guys say that the B&M coolers are made by Hayden, but much more expensive. I'm not sure if that's actually true, but the Hayden 676 ($36 from Amazon) does look pretty close to the B&M 70255 ($75 from Jegs). I'll have to look into that. The stock setup goes into the bottom of the radiator, which makes it more of an A/T fluid heater than anything. A C6 tranny should be ~150F, not 200F...

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