Overheating Paranoia

[92EcoDiesel Jetta]

I looked at the wiring diag. for my Jetta and the rad fan switch has 2 sets of contacts, one at 95C and the other at 105C for low speed and high speed fan. I jumper-ed the power input pin of the rad fan switch connector to the low and high speed contacts and the fan works on both speeds. My next task is to pull the rad fan switch and test it in hot water to make sure the switch contacts works at the correct temps.

I pulled the rad fan switch and tested it in boiling water and neither sets of contacts worked. The switch has no brand/ temperature, or part number markings on it (probably Meyle or some equiv junk). Luckily I have a spare used radiator from a 91 Eco with a good rad fan switch marked Wahler 191959481C  95/ 102 C. Tested it in hot water to make sure both contacts work and installed it (takes a 29mm socket BTW).

The rad fan switch directly powers the rad fan and that is quite a bit of current going through those poor contacts. My guess somewher's around 12 to 15 amps. I may put a relay in there to increase switch life (hopefully life of the engine) since changing it is a PITA messy job having to spill coolant.

[92EcoDiesel Jetta]

 My rad fans are working again.  The low speed comes on at midway between 12 o'clock and the 3/4 mark. My temp gauge normally sits slightly past 12 o'clock so  it's not a real big temp swing before the fan comes on. I am happy with the way it works. If I get ambitious, I may calibrate the temperature gauge

[92EcoDiesel Jetta]

When the low speed fan kicked on, which was supposed to be at 95°c per rad fan switch rating, the hose by the coolant temp sensor at the head was  90C per the IR thermometer. The coolant inside the hose must be hotter than that. I am going to calibrate the coolant temp gauge and put numbers on it.

[rs899]

I am only getting one speed on the fan, I assume low.  What do I do /look for to get it to go high speed too?

[92EcoDiesel Jetta]

I am only getting one speed on the fan, I assume low.  What do I do /look for to get it to go high speed too?

 Remove connector on rad fan switch. If three terminals you have 2 speed fan. Two terminals one speed. Jumper the hot terminal to the other two terminals. If both fan speeds work, you have a bad rad fan switch.

[92EcoDiesel Jetta]

To calibrate the gauge I put a spst switch on one terminal of the temp sensor to measure its resistance by switching it between an ohmeter and the temperature gauge. Once I get the resistance readings at the points of interest on the gauge then I can go on to the next step.

[mtrans]

You guy`s are nothing!
Fan go ON on idle but in drive no???
Manuel swich,new rad,pump,fuel and oil fiter(to clean cooalant) vinager.....etc
Nothing?
Shpo man didn`t belive me.


A...It`s is AIR -for most of time.
or gremilin from ORCoaster.

[92EcoDiesel Jetta]

I have a diesel cluster I just picked up with a red LED at top center of the coolant temp gauge. Is that an overheat warning? How does it work (what triggers it)? What model/year is the cluster from?

I been driving around with  a working rad fan again and there's no big swing before the fan comes on, (needle moves 1/16 inch). I have a 195F T-stat

[wolf_walker]

Low coolant level light from a later jetta/golf I believe. My 85 TD had one. Two prong sensor in the tank, think it might read coolant mixture too, can't recall but it isn't an on/off switch though I'm pretty sure.

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[Rising]

I'm paranoid about this too. But an aftermarket mechanical gauge measuring off the front coolant neck really put me at ease.

Although I'm curious about these radiator shrouds you guys mentioned. I've been thinking of fabbing some up for mine just on principle. Too much room for air to go elsewhere.

Does anyone run oversized radiators or the like from other cars? I'm always interested in keeping this thing cool.

And can a coolant level sensor be added to a mk1? What cars came with them. I def want one after my little incident....

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[wolf_walker]

You can get a tank that has the threaded opening for the sensor, all cheap.
I believe the wiring isn't straight foward. 
The A2 Bentley has a section on it I'm pretty sure. 

[damac]

I had to change the oil on my rabbit the other day and noticed that my vbelt was really loose.  Like one finger on the pulley and I could move it loose.  To be honest I haven't touched this since I installed it new almost 10,000 miles ago when I put the car on the road

I also had the manual gage on the car that whole time but now wonder if mine is running right or was heating up too much before from that loose belt.  I put in a "better" rtd sender for my auber gage and noticed the car runs real close to 175 steady with the sender on the head to radiator flange.  Car really didn't heat up much when stomping on it unless pulling a hill, but sitting in dead stop traffic is what showed the gage hit 185 and then the fan would come on and soon bring it down to 175 again.

I have a stock thermostat I thought.  I think I need to get one of those temp guns

All I did was take the fan sensor off what was on the car, never even looked into its setting.  I tested the thermostat in a pot and it did the job.

I am still guilty of not having the radiator diverters even though I don't believe I have any cooling issues.

[wolf_walker]

175 seems pretty low.  Stock t-stat starts to open at 186 or so.
Only ten degrees but still.  I'd prefer a higher and more static temp if
I was given a choice.  FWIW a belt can sure slip on a pump, but it does not
take much to drive one, especially with a lot of contact area, even if it's loose contact.

[92EcoDiesel Jetta]

175 is low. I run a 195F stat and my gauge sits 1/4 of the way between the mid and 3/4 mark in normal driving. No big hills around here but going up short hills the needle does not move. Only when in traffic for 5 minutes before the gauge moves enough then the fan kick on low for a minute then shuts off.

I have been monitoring the resistance of the temp sensor and the voltage across it while I drive in my effort to calibrate the gauge. So far so good. I can see minute changes in the sensor that is not perceptible in the gauge. E.g. if I let off the throttle and put it in neutral rolling down a hill, the temp as seen by the sensor actually goes up. I would have thought it would go the other way since the engine is idling doing less work. The explanation I came up with is that the water pump is not moving as much coolant at idle as cruising and the heat from the head is heating up the stagnant coolant more.

[wolf_walker]

175 is low. I run a 195F stat and my gauge sits 1/4 of the way between the mid and 3/4 mark in normal driving. No big hills around here but going up short hills the needle does not move. Only when in traffic for 5 minutes before the gauge moves enough then the fan kick on low for a minute then shuts off.

I have been monitoring the resistance of the temp sensor and the voltage across it while I drive in my effort to calibrate the gauge. So far so good. I can see minute changes in the sensor that is not perceptible in the gauge. E.g. if I let off the throttle and put it in neutral rolling down a hill, the temp as seen by the sensor actually goes up. I would have thought it would go the other way since the engine is idling doing less work. The explanation I came up with is that the water pump is not moving as much coolant at idle as cruising and the heat from the head is heating up the stagnant coolant more.

Makes sense.
Reminds me of another counter intuitive thing I noticed on a TD years ago, coolant, and oil, temps were higher with less fuel when under sustained boost (interstate with AC on).

I wish there were more clean places to put gauges in a Rabbit, I've got the three in the lower console but anything else is going to be kinda gaudy. 
I guess if I was less lazy I could recess small LCD displays somewhere.