Thermo fan switch & 82C t-stat comments

LM · Aug 28, 2003

For 16V, but may have some 8V overlap

Many of us are familiar with the Townsend recommendation to run an 82C t-stat in hot climates, paired w/a VW/Wahler 6010.82D thermo fan switch, or equivalent (stock setup is usually 89C t-stat & 92C switch [87C-92C range])

I made the change this past spring, and thought "great"

But as the summer temps came, I noticed my cooling fans were running _while cruising at high speeds_, which shouldn't be happening (w/a good rad) - fans should be cycling/running during stop n go driving, city driving, poss at low road speeds, and sometimes after hot-engine shut down. The dash temp gauge was at 1/2 (ambient temps ≈+32C/90F), yet the fans were almost constantly on at higher road speeds (with A/C off)

Researching more, I found the 6010.82D's actual range is 77C-82C: so the rad switch is closing - actuating the fans - before the t-stat even really starts to open! Since this is happening at higher speeds, the fans running may not even be heard above the usual noise. This is just excessive, unnecessary wear on the fans (and alt), aka Fan Abuse :!

With respect to all the great info on the Townsend site, I changed to a Wahler 6010.88D rad switch (83C-88C) [for those in the US available here], which has been a great match w/the 82C t-stat. Wahler also makes a 6010.85D (80C-85C) switch, too. There may be some variance wrt t-stat brand used, rad condition, driving conditions, etc

Wahler 82C 3-position thermostat PN 4154.82D

p.s. - Wahler PNs from Wahler, Germany - don't know for sure if they are global PNs

Armando · Aug 29, 2003

Interesting explanation especially because some of us, at least me, are novice and most of the technical data are as they are introduced by the different manuals and/or reports.

However, my 1991 900 Conv LPT (82 stat and 82 t/switch) does not warms up that much at motorway speed. She did with the old radiator, but I've recently changed it for a new one. I drove for 250/300 km two weeks ago and (as you probably heard in Italy the air temperature during the day was never below 34/35°) even driving at our speed limit 130 km/h the temperature gauge set always at the first third and the radiator fan is used to kick in only during city driving.

Thanks for your info.

Armando

lernst · Aug 29, 2003

I just went to the 82 deg set-up last week and I'm a bit suspicous of the whole thing also. To me, the temp gauge should always be at or above the "mid-mark". Since the conversion, the gauge fluctuates (frequenlty) from just above mid to just below. My fans used to rarely come on, but know it's pretty frequent. I'm going to keep my eye on it and give it some more thought.

Matthew · Aug 29, 2003

lernst said:
To me, the temp gauge should always be at or above the "mid-mark".

IMO the temperature gauge, assuming some level of accuracy, should be between 1/4 and 1/3 on the scale. If you live in an excessively hot climate, then yeah maybe it'd be at 1/2 but no higher.

Your fans may have been largely inactive due to a dodgy thermofan switch, and now you've replaced it's maybe highlighting other issuess.

When was your radiator last replaced?

__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote

Smithy · Aug 29, 2003

I found for me that the most useful mod was to replace the thermostat to an 82C one and wire in an manual override switch for the fan. when I first bought my car, I did have a few running hot issues..... The running hot at motorway/freeway speeds was cured by fitting a new radiator. But the issues were never really cured until the head was removed and the head and block cleaned out. Now my car runs at 1/3 on the temp scale, moving to 1/2 in traffic. Of course if I am sitting in very dense traffic, the scale moves up into the 3/4 and the fan kicks in... all very normal. Because I have a fan override switch, in very dense traffic, I can switch the fan on manually and crawl in this traffic with the temp guage, never moving from the 1/3 scale. The fan moves as much air into the engine bay as travelling at 30 MPH.

LM · Aug 29, 2003

lernst said:
Since the conversion, the gauge fluctuates (frequenlty) from just above mid to just below. My fans used to rarely come on, but know it's pretty frequent.

If the fluctuating is a jumping or bouncing, and happening while at steady state cruise, something's askew. What brand of t-stat? I wonder if it might be an aftermarket 2-position vs and OEM 3 position?

--

I should have said more specifically earlier, that at cruise, my temp gauge usually reads 40% at high ambient temps, sometimes moving to/peaking at 50% if I'm getting on it. I had to listen hard to hear the fans running (at 40%-50% gauge), with the former 77C-82C rad switch.

With the (new) 88D | 83C-88C switch, fans now come on approx 2/3 gauge or less, which seems a good target figure. The two fans are pretty efficient at quickly bringing the coolant temp down.

lernst · Aug 30, 2003

LM said:
If the fluctuating is a jumping or bouncing, and happening while at steady state cruise, something's askew. What brand of t-stat? I wonder if it might be an aftermarket 2-position vs and OEM 3 position?

Factory Saab 3-position. I'm guessing things are probably fine, it was just a bigger change than I was expecting. Also my fans are a little noisy, so every time they kick in I question how long they'll last!

Fred · Aug 30, 2003

LM, good topic to raise, here's my experience.
The Townsend advice seems good, to avoid having the engine water temperature varying and all the differential expansion problems stressing the gasket must be a good thing. I went for hotter stat and the standard switch.
When I first got the LPT the temperature gauge seemed to be connected to the speedo, faster = hotter. I changed the thermostat for the cold climate (92C!, well this is Wales) and left in the standard thermoswitch. Bottom half of radiator was then obviously doing nothing. I had the Rad recored with a high capacity core by the excellent man in Llanwrst (hand made radiators).
Since then the temperature gauge doesn't move after the car is warmed up, just stays a little above centre. Fan (no AC) comes on and cycles if it's left idling hot, with a slight rise on gauge. All the load dependant temperatures changes have gone, even this summer.
Fred

LM · Aug 30, 2003

Hey Fred. I would use the stock set-up for normal-to-cooler climes, too.

What I don't get about the Townsend recommendation - both in theory and applied - is that the 82C t-stat is sometimes closed! while the 77C-82C switch is sometimes running the fans?!

I did find the temp guage to be quite stable with the paired 82C's, but with the brunt of the cooling placed on the fans, vs the rad

The Wahler 6010.85D (80C-85C), paired w/an 82C t-stat, would effectively mimic the stock "straddle" of the 87C-92C rad switch, and 89C t-stat pairing. So some may want to try that instead

p.s. Behr-Thompson seems to be another good cooling system vendor - I don't what/if they have any c900 offerrings

Fred · Aug 30, 2003

I wonder if the dead band on the fan switches is as tight as claimed? I'll bet they set them up for the switch on setting. A few degrees wrong, so it's a 75/82 rather than a 77/82, would leave the thermostat and fan switch fighting one another?
Or could be that the standard rad can't hold 82 on a 30 ambient without the extra airflow. Aiming higher on temperature does make the cooling systems job easier.
Fred

pusko · Aug 30, 2003

Let's say you have 82c stat and 82c switch. Your fan come on every minute.
What if you drill a little tiny hole on the thermostat, so a very small amount of water circulates constantly through radiator.
Is this possible? Is it advisable?

walawala · Aug 30, 2003

pusko said:
Let's say you have 82c stat and 82c switch. Your fan come on every minute.
What if you drill a little tiny hole on the thermostat, so a very small amount of water circulates constantly through radiator.
Is this possible? Is it advisable?

I think that'll make no use of the thermostat? Correct me if I'm wrong.

Like me, I removed my thermostat. It takes alot longer to heat up to normal operating temp and hasn't gave me any probs so far. But I prefer the colder 82C switch as it is hot here.

LM · Aug 30, 2003

LM said:
What I don't get about the Townsend recommendation - both in theory and applied - is that the 82C t-stat is sometimes closed! while the 77C-82C switch is sometimes running the fans?!

Thinking about the (not quite right) above some more

Using 82C switch (77C-82C) & 82C t-stat pairing:

During cold engine start: t-stat closed, no coolant flow to rad, which is good to bring block temp up faster to desirable operating range, where engine is most efficient/least wear

Coolant temp at rad will be much colder, as is not yet receiving hot flow from block, so rad switch will be open/fans off

Coolant gets to 82C and t-stat starts to open, sending hot coolant to rad: the rad switch then soon kicks fans on

Then think question is whether the t-stat "positions" are discrete, or if they blend into one another (has been a while since I've thrown a t-stat into pot o'hot water, for pre-install ck). Maybe t-stat stabilizes at partway (vs fully) open to position 2, and rad switch is running most of time? Seems like they would be fighting each other? or at least not an optimum pairing

There is a tiny hole in EOM t-stats: helps w/bleeding but don't think it does much else

Townsend down now

Have an excerpt on my HD

"Saab thermostats are special. They have a three position operation. the first position is full closed and it blocks all flow to the radiator until the engine warms up. The second position allows flow both to the heater core and the radiator to provide cabin heat and cool the engine. This is the position the thermostat should be in most of the time while driving. The third position of the thermostat allows full flow to the radiator and blocks flow to the heater core as the plate on the bottom of the thermostat blocks the passage to the pipe to the heater. The thermostat reaches this position when the engine is nearing overheating and allows coolant to flow directly to the most efficient heat exchanger, the radiator. The heater core is bypassed because the heater valve has bypass circuits in it and is not exposed nor has the flow capabilities of the radiator. This allows for maximum cooling of the engine when it is needed. Aftermarket designs usually do not incorporate these three positions, only two. The biggest complaint from people who use incorrect aftermarket thermostats is no heat after the car warms up in the winter. Saab supplies two thermostats, an 89 and an 82 degree unit. We highly recommend using the 82 degree unit to keep the engine as cool as possible but still within its designed operating temperature."

Fred · Aug 30, 2003

Thermostat's are progressive in action, so will settle at a position which allows just enough flow through.
Agree on the little hole in stat, sometimes has a small float in it, intended to allow air (and combustion gas!) to pass the closed stat and bleed out.
Fred

Armando · Sep 1, 2003

Just last weekend I flushed the cooling system as I changed the exhaust manifold gasket. When I finished I had to fill the cooling circuit again and, obviously, bleed it.

My LPT 1991 is now with a Saab 3 stage Tstat 82° and a termoswitch 82°. When I bleed the cooling system I leave the engine reaching the normal temperature. What I've noted is the following:

cold engine: upper right corner hose cold.

warming up: lower left corner hose warm but upper right still cold.

warm engine (temp gauge 1/3): upper right corner hose starts getting warm [stat opens???], but the fan does not kick in.

My conclusion is that stat opens before 82° temperature and this temperature may be the indication of heater bypass position.

Tell me if I'm wrong.

Armando

pusko · Sep 1, 2003

Is there any good 78c or 80c thermostat for my c900 1983?
To buy on-line?!

Fred · Sep 1, 2003

Armando,
I think what you're seeing with the lower hose getting hot first is due to circulation of turbo bearing cooling water, which happens regardless of stat.
If I think on it I'll check what the NA warms up like and see if it does the same.
Fred

LM · Sep 3, 2003

It seems "three position", as described by both Wahler and Townsend, is a misnomer and really doesn't apply to the _t-stat_, but rather the _application/cooling system_ they're used in.

I.e., it's the porting of the t-stat housing/hose arrangement that will prevent/direct coolant flow, per the progressive t-stat position
-----

Armando - do your fans come on in city driving at about 40% - 50% gauge?

bunny hopper · Sep 3, 2003

Hello all.

LM, my fans kick in about the halfway mark during SLOW city driving (by driving I of course me mostly idling and rolling forward a bit) on our T16.

The after-run fans cycle after a lot of city driving, too.

LM · Sep 3, 2003

bunny hopper said:
LM, my fans kick in about the halfway mark during SLOW city driving (by driving I of course me mostly idling and rolling forward a bit) on our T16.

The after-run fans cycle after a lot of city driving, too.

And which rad switch and t-stat are you running?

bunny hopper · Sep 4, 2003

LM, I'm running an 89 'stat with 92 fan switch. I thought earlier this summer about going down to the 82/82 pairing (while it was regularly 35C outside) but thought to just go with what was working!

The thing that I've noticed is that there's fair fluctuation in my temp guage when driving around in the really sunny heat, from stop and go to highway, etc, that maybe there wouldn't be with 82C setup? I guess that fluctuation comes from the fact that the fan kicks in at a different temp than the stat's opening and closing? So the fluid circulates, heats up, gets cooled by the fan, heats up, etc, etc?

It's interesting that your fans are cycling so much to keep the coolant at 82C - I guess that it's a question of stressing the whole system with more temp fluctuation or have the fans cycling more often?

I don't know enough about the physics of the cooling system to really form my own conclusions, but am trying to understand more!
cheers.

LM · Sep 4, 2003

I think the 89 'stat with 92 fan switch is a good year round combo for your latitude.

Stop n Go is tough on the cooling system - not sure how much gauge fluctuation you are seeing? Could be normal, or could be several possibilities from poor dash or temp sender grounds, old t-stat?, old rad? block & head coolant passages need cleaning, etc (don't know cooling system history)

Crux of orig post is that is that fans are coming on at _highway speeds_ but shouldn't be [82C (77C-82C) rad switch too cold for 82C t-stat, IME]

Armando · Sep 4, 2003

LM said:
Armando - do your fans come on in city driving at about 40% - 50% gauge?

Yes they do, I should say it does, because only one fan kicks in if the A/C is switched off.

Thermo fan switch & 82C t-stat comments

Our Vendors

Top Contributors this Month

Recommended Communities