Topping up a viscous fan - what effect?

Submitted: Friday, Jan 04, 2008 at 22:01
ThreadID: 53116 Views:4425 Replies:8 FollowUps:4
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Hi all,

Having problems when towing the camper with the Courier uphill on hot days.

I think I've narrowed it down to two potential sources. I've got two possible problems.

First I'll look at is cleaning all the bugs and crap out of the air con condenser. It needs to be done anyway, and I hadn't realised how bad it was.

The second is the viscous coupling which appears at the moment to be working in some manner approximating normal.

But if I wanted the fan to work harder - pull more air - and not slip when it's at the lower end of it's lockup threshold, would adding more fluid make it do that?

The symptoms I'm getting when towing the camper (1.4 tonne) on a really hot day are that when I hit a hill - say the climb into Omeo - I can hold speed (eg. 60kmh in 3rd) and even accelerate so I'm not at the limit of the gear, but after half of the climb the temp guage climbs toward hot rapidly.

Dropping back to say 40kmh and 2nd gear the temp guage drops rapidly. (Dropping speed staying in 3rd just ends up dropping out the bottom end of the rev range and it labours.)

In anything less then about 32°C its not a problem at all.

I've noticed it once before a few years ago not towing when I was heading to Ceduna. Trying to hold 115-120kmh into a hot headwind did it, which I put down to effectively trying to drive it at 140kmh (counting the headwind) in hot weather. Dropping speed back to 100-105kmh fixed it then too.

I've got some of the Toyota viscous fan coupling fluid. I'm wondering if it's worth performing surgery on the fan.

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Reply By: Footloose - Friday, Jan 04, 2008 at 22:25

Friday, Jan 04, 2008 at 22:25
Dave, have you had the thermostat checked ?
The viscous coupling can cause the problem. Adding fluid enables the clutch to "latch", and so the fan blows cold air at speed. It can start to disengage under load if not enough fluid.
AnswerID: 279839

Reply By: Bonz (Vic) - Friday, Jan 04, 2008 at 23:17

Friday, Jan 04, 2008 at 23:17
I recall reading an article ages ago about re-fluiding the viscous clutch. Pull it apart, clean out the gunk, reassemble and refluid it. I would give that a try too Dave.
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AnswerID: 279844

Reply By: Member - Mike DID - Saturday, Jan 05, 2008 at 06:46

Saturday, Jan 05, 2008 at 06:46
When you're travelling at 80km/h plus, I wonder how much airflow increase you actually get from a fan, compared with the ram-air effect.

In cars with no mechanical fan - just electric, the fan doesn't operate except in slow traffic.

Rather looking at removing heat, maybe you can look at producing less heat - checking that the engine is tuned to run most efficiently ?
AnswerID: 279862

Follow Up By: geocacher (djcache) - Saturday, Jan 05, 2008 at 22:42

Saturday, Jan 05, 2008 at 22:42
Hi Mike,

Problem is more evident at lower speeds. I wish I could maintain 80kmh up the hill into Omeo :o(

Some of the climbs - eg. from Omeo Hwy up onto the high plains heading to Falls Creek are persistent and steep, and the problem is occurring at far lower speeds than 80kmh.

Just being able to hold 50-60kmh in third would be nice.

FollowupID: 544197

Reply By: Member - Olcoolone (S.A) - Saturday, Jan 05, 2008 at 07:50

Saturday, Jan 05, 2008 at 07:50
Most vehicles are designed for anything over 40 to 60 Kph the fan is not needed.

Viscous fans are designed to operate at no more then about 3000 rpm or they may fly apart, if you put more viscous fluid in it wont allow the fan to slip increasing the chance of damage, excessive noise and poor fuel economy.

Regards Richard
AnswerID: 279871

Reply By: Member - Kiwi Kia - Saturday, Jan 05, 2008 at 10:59

Saturday, Jan 05, 2008 at 10:59
If you do pull it apart be very careful. I found that the large 'O' ring stretched and would not go back in the circumference groove. Also, a VERY small (only a few match heads in size) wiper block got lost. I was replacing the complete unit so it was not really important to me but I was thinking of tossing it 'under the bench' for a spare.
AnswerID: 279899

Follow Up By: Member - Roachie (SA) - Sunday, Jan 06, 2008 at 22:03

Sunday, Jan 06, 2008 at 22:03
Same thing.....identical....happened to me !! Damn thing was a throw-away. I think it's not so much of a problem if you do it REALLY quickly (IE: don't disassemble it, go in for dinner and a cr@p and then come back to partially, squirt in some extra fluid and get the mother closed asap).
FollowupID: 544374

Reply By: Catfish - Saturday, Jan 05, 2008 at 11:08

Saturday, Jan 05, 2008 at 11:08
Hi Dave,

I used to have a BJ70 SWB Landcruiser. When I first got it the temperature gauge used to climb into the red when driving at highway speeds (not towing). I replaced the thermostat - no effect. Removed the Radiator and got it rodded out by a radiator shop - still no fix. and the last thing was to remove the viscous coupling on the fan and put new oil in it - problem solved!!
Even though my overheating problem was at highway speeds it still required the fan to keep it cool!.

By the way we did check the water pump impeller too, it was OK.

AnswerID: 279901

Reply By: geocacher (djcache) - Saturday, Jan 05, 2008 at 22:44

Saturday, Jan 05, 2008 at 22:44
Is it worth considering a manually switched electric fan on the front of the air con condenser?

AnswerID: 280001

Reply By: geocacher (djcache) - Sunday, Jan 06, 2008 at 21:56

Sunday, Jan 06, 2008 at 21:56

Pulled out the radiator today. Once the fan cowling was off I found a contributor to the problem.

At some point when I've been up to the windscreen in a river the fan blades have barely scraped the radiator, but enough to have nipped the fins over between the cores. It hasn't done any damage to the cores.

But it had reduced the available area of the radiator by 25-33% by estimate. And the area affected was the area that the fan would normally achieve greatest flow through.

I'm thinking that if the fan hub is working correctly and it looks to be, that the reduction in airflow is not so great that it affects normal operation, but that under load it causes it to overheat.

I think I'll leave the fan hub and try the radiator - spent three hours today with a tool made out of a junior hacksaw blade straightening fins. More to do tomorrow, but at $320 for a new one I'm figuring on making a very boring $30 an hour at least.

No point fixing several things and not ending up knowing what the solution was.

AnswerID: 280168

Follow Up By: Member - Roachie (SA) - Sunday, Jan 06, 2008 at 22:11

Sunday, Jan 06, 2008 at 22:11
Sounds like a fair plan Dave...... try it before you put more fluid in the viscous hub. The trouble with doing 2 or 3 or 4 things all at once is that, if it works, you don't really know which one of the "things" was the one that did the job.

Do you have a plan to stop the fan hitting the radiator in future? One thing I have heard of (but have not seen it done) is to stop the engine (before entering the water.... also allows the diffs to cool down), then tie some string/cord etc around one of the fan blades and tie it off against something under the bonnet to prevent the fan from turning. Obviously you need to get the cord off asap after completing the crossing. Has anybody tried this?
FollowupID: 544377

Follow Up By: geocacher (djcache) - Monday, Jan 07, 2008 at 13:20

Monday, Jan 07, 2008 at 13:20
Hi Roachie,

i could avoid really deep puddles in future...

But that's no fun.

I've spoken to my mechanic today and decided to order a new radiator rather than stuff around.

Besides at 5 years old it's no spring chicken. It'll never be the same as new again. And with plastic top & bottom tanks exposed to heat I'm still a sceptic. I'd rather replace it now for a few hundred bucks than have it fail in March in the heat somewhere north of Iron Knob on the way to Speed Week.

I will pull the water pump off while I've got the radiator out and have a gander at it and see what 130,000 km of electrolysis has done. I don't suspect it will show much if any responsibility for the problem.

As to the cord idea I'd not be attempting it. Just letting it cool down should be enough any way. Once it's "'relaxed" to the point where the cord will stop it the water should do the same thing anyway. I'd say this has occurred on a trip where I didn't take enough care. A blind on the bullbar would be the preferred solution in future.

I'd has at a guess that if you thermocoupled up a diff you'd notice bugger all cooling from a 5 minute stop before a river crossing. That's why I extended the diff breathers.

The diff has a huge thermal mass, and steel to air has a poor temperature transfer coefficient. I would be very surprised if you got much more than a couple of degrees cooling in 10-15 minutes.

FollowupID: 544474

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