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  #1  
Old May 25th, 2006, 09:08 PM
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Jonah Thompson
1994 D90 ST
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Temp Gauge question

1994 D90 3.9

my truck has been running flawlessly since I bought it last year - till yesterday. The temp gauge usually runs right in the middle unless I'm really working it, then it might drift a little higher. Yesterday It started and warmed up in a few minutes (~10) then suddenly the needle jumped right up to the edge of the red and stayed there. It's done the same thing today, if I start the truck warm the "normal-middle of the gauge" time is a little less, maybe 5 minutes, then the same thing. checked all the fluids, everything full, changed recently and from what I can tell from the previous owner(s) maint records (incomplete) the service has been kept up. Not sure where to start looking.
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  #2  
Old May 25th, 2006, 11:18 PM
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Doug Walker
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Check that your viscous fan clutch hasn't gone bad. You can really hear the engine fan LOUDLY when the fan is engaged. If you can hear the fan ROAR when engine is hot, the clutch is good. If not, the clutch is letting the fan slip. There are other ways to check the clutch >>> Anyone else?

Doug W.
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  #3  
Old May 25th, 2006, 11:34 PM
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Dave Souza
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Does it spike when driving, or at idle? Can you actually tell that engine is hot? If the guage is accurate that engine bay should be mighty hot. Which edge of the red? was the needle pegged to the right, or just getting to edge of the red?

My experience is that overheating at an idle or slow speed is usually the viscous fan, overheating underload at high speeds is clogged radiator tubes.

However, when my viscous clutch goes bad the truck tends to slowly just keep heating up, a quick spike might just be the thermostat closing or even a bad guage.

Another check for the fan, when the temp spikes (and the truck is truely hot) shut of the truck and attempt to spin the fan with your hand. If it freewheels, its usually bad.
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  #4  
Old May 26th, 2006, 08:23 AM
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All good advice.

One tool that really helps is an Infrared Non-Contact Thermometer/ reader. These are about 60 bucks at the local auto parts store. You point them at something and it gives you the temp. When you have one you can double check what your real engine temps are. The guages can be way off and can trick you into buying parts you don't need and even worse, running an engine you think is cold when it is actually too hot (just like NAS 110s with that stupid "signal conditioner" that never lets the guage show the real temp).
Its nice to be able to compare that the guage says "hot" but the engine is running at 180 degrees. That makes it easy to diagnose you have a gauge problem, not an engine problem (and vice-versa).

Clucth fans when cold should have some mild resistance to spinning. If before you warm the engine up you can spin the fan and it spins freely its time for a new viscous unit.
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  #5  
Old May 26th, 2006, 10:51 AM
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Jonah Thompson
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yup, fan spins freely when hot, I was fooled because it's spinning when running. I see the electric -vs- replace viscous debate is fierce. What am I looking at cost and time wise to do either?
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Old May 26th, 2006, 11:01 AM
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Can you remove the factory temp gauge and replace it with a real gauge (with actual numbers) in its place? You'd need to add the correct sender of course. Or does the ECU need the input from the factor gauge?
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Old May 26th, 2006, 11:12 AM
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The ECU does not need input form the guage sender. It gets its signal from another sensor on the intake.
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  #8  
Old May 26th, 2006, 11:19 AM
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I replaced my temp guage with a VDO vision guage. Just needed the proper adapter to screw into the housing on the block. I found it in a Sunpro adapter pack at a local Autozone.

I think going rates for viscous untils are in the $175-200 range. Check AB or RN, others. The standard electric fan swap everyone's doing is the Flex-a-lite 210 fan kit, right now $237 from Summit Racing. Add in another $20 for the VW temp switch, plus whatever time it takes you (or pay someone) to do the switch.

It costs a little more for the electric fans up front, but the viscous unit is a maintenance item, and will need replacement every few years, I think 5-6 is supposed to be standard. My last viscous only lasted about 3 though, and I'm in the middle of the fan swap now.
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  #9  
Old May 26th, 2006, 04:53 PM
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I have to disagree on the fan swap, having had both. IMHO, keep the viscous setup, it pulls way, way more air when engaged. Just remember it's a maintenance item tho. Also recommend changing out the thermostat that switches on the A/C fan to a lower reading one -- info is elsewhere on one of the threads.

Doug W.
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Old May 26th, 2006, 05:01 PM
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Jonah Thompson
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Doug - you are refering to the A/C cutoff thermostat? If I understand correctly this is supposed to shut off the A/C if the engine temp exceeds the value (~225* or something like that) What temp rating is being suggested?


As for the swap, still debating it. FAL lists the 210 as 2500 CFM, any idea what the belt driven stock one is?
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Old May 26th, 2006, 05:28 PM
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I'm a computer idiot and I don't know how to link to a thread so here's a copy and paste from a thread a while back. I did this exact same mod after getting some suspect hot readings from my stock gauge. With this setup I could see that I was running between 180-195 99% of the time and I wasn't overheating as the stock gauge was indicating.


I just replaced my stock water temp gauge with a mechanical gauge(AutoMeter part# ATM 2606). I purchased from egauges.com (http://egauges.com/vdo_mult.asp?Typ...=Z-Series&Cart=). I used an adapter from SunPro so that the probe goes directly where the electronic temp sender is. (http://sunpro.com/product_detail.ph...3b684f92fa7291e) It's so much nicer (piece of mind) to read real temperature reading. I will post pics if interested.

Nilo
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Old May 26th, 2006, 05:34 PM
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Jonah, it's the coolant temp sensor in the casting just before the top tube to the radiator. My understanding is that it controls when the AC fans kick in when the AC is shut off. I hope it doesn't also control the AC compressor as well. I thought that function was from one of the other coolant sensors. Anyone know?

Doug W.
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Old May 26th, 2006, 05:41 PM
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Quote:
Originally Posted by PT94D90
I'm a computer idiot and I don't know how to link to a thread so here's a copy and paste from a thread a while back. I did this exact same mod after getting some suspect hot readings from my stock gauge. With this setup I could see that I was running between 180-195 99% of the time and I wasn't overheating as the stock gauge was indicating.


I just replaced my stock water temp gauge with a mechanical gauge(AutoMeter part# ATM 2606). I purchased from egauges.com (http://egauges.com/vdo_mult.asp?Typ...=Z-Series&Cart=). I used an adapter from SunPro so that the probe goes directly where the electronic temp sender is. (http://sunpro.com/product_detail.ph...3b684f92fa7291e) It's so much nicer (piece of mind) to read real temperature reading. I will post pics if interested.

Nilo
I think the actual #s changed at E guages, but they were nice enough to help me with the new ones, of course if I had the #s I would tell you but I sold the records with the that truck.
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  #14  
Old May 26th, 2006, 06:18 PM
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Dave Souza
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I'm getting confused here myself with the different sensors. The A/C cutoff switch is right on the same housing as the thermostat, has two male spade poles and usually has a small brown plastic connector (two wires of course). My understanding is this kills the AC at like 220 or something. This is what we usually remove to put in the VW temp switch.

The sender used for the guage is a little down and to the left of that on the casting, when looking in from the engine bay, and it has only 1 wire.

Those are the only two that I'm aware of... I have no idea if, when, or how the A/C aux fan is turned on with the A/C off, and the truck begining to run hot. I don't believe mine ever did that. I thought that one was ECU controlled, but I don't really know that for sure. Eventually my A/C system had the A/C fan hardwired to always run with the A/C due to it running warm with the A/C on down in Fl. Kind of a hack job but it worked.

I've also thought of just installing a pusher fan like the A/C aux fan, and running that with the stock viscous fan setup. I'd hook it up with the VW switch so it'd only come on at 200 degrees. I run a 160 degree thermo, so I think it'd only come on in traffic or on the trail.

Follow-up Post:

Just thinking about the stock fans pulling more, etc., on Dougs post. I go back and forth on what I think is better electric or viscous. The viscous is certainly simpler, and its easy to just swap the viscous. its just that I think it's expensive to keep spending almost 200 bucks every couple of years on that damn thing. I'd be on my third if I replace again instead of electrics, and thats in only 5 years of ownership.
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