WUR ohms question

[Hoffmanmotors]

I read that the ohms for the WUR heat element should be 18-22 ohms. I just tested my WUR and it reads 35 ohms. Is this bad? Is to much ohms bad or is to less of ohms bad? Sorry if this sounds like a stupid question.

Also is the heater element in the WUR vital to the performance of the car?

TIA
-Jeff

[Hoffmanmotors]

Anyone......

Anyone......LOL

[Hoffmanmotors]

bump

[Won]

I can't tell you whether too high or too low a resistance is good or bad, but I can tell you this: inside my WUR, there's the bimetallic strip for the normal WUR function, then there is a second bimetallic strip that is adjustable for open/close position that changes the resistance measured at the plug on the WUR body. If I remember correctly, when starting from cold the second strip (which is exactly like a room thermostat) is open, and when the heating element reaches a certain temperature (this is the adjustable part) the heat then closes the "thermostat" and it reduces the overall resistance of the element. I've read here that the lower the resistance, the hotter the element gets and therefore quicker "warm-up" time for WUR. I had both the WUR and AAR apart and bench tested to sort of "synch" them and I can set the "thermostat" to close anywhere in the last ~1 minute before both of them reach "warm" condition, and it won't make much difference once they're in the car.

So if the resistance vs. heating time relationship is correct then your 35 ohm WUR should take longer to reach the "warm" operating temperature. People say the WUR will heat up eventually from the engine heat, but with mine I had no luck getting it warmed up without the 12V input; I accidentally left it unplugged once and the car just did not run right, even after 30 minutes or so of driving. Eventually, once the engine's been running for a long while then the WUR will eventually heat up, but that certainly takes longer and is less controllable than using the heating element.

[Jim Williams]

I can't tell you whether too high or too low a resistance is good or bad, but I can tell you this: inside my WUR, there's the bimetallic strip for the normal WUR function, then there is a second bimetallic strip that is adjustable for open/close position that changes the resistance measured at the plug on the WUR body.

Won,

Could you post the Bosch number of your WUR that has the two heating elements?

Most of them I've had open have only the one element, and I'd just like to know which has the two elements.

Thanks......

[boyt911sc]

Originally Posted by Hoffmanmotors

I read that the ohms for the WUR heat element should be 18-22 ohms. I just tested my WUR and it reads 35 ohms. Is this bad? Is to much ohms bad or is to less of ohms bad? Sorry if this sounds like a stupid question.

Also is the heater element in the WUR vital to the performance of the car?

TIA
-Jeff

Jeff,

The heater element is a vital and critical part of the WUR. Not all WUR have the same heating resistance (Ohms). So this depends on what number or type of Bosch WUR you have. The amount of resistance in a given WUR dictates the heating characteristics or slope of the WUR. The factory calibrated heating resistance varies from model to model. For example:

WUR (0-438-140-045) for '78SC measured @ 24 ohms
WUR (0-438-140-089) for '80-'83 911 Euro measuredd @ 31 ohms
WUR (0-438-140-009) for '73-'75 911 measured @30 ohms

WUR (0-438-140-084) for '81-'83 Saab measured @ 46 ohms
WUR (0-438-140-136) for '84-'88 Saab measured @ 47 ohms

So what's the number on your WUR? If you have a 31 ohms resistance it simply means it takes longer to heat compared to a 24 ohms resistance. keep us posted.

Tony

[Hoffmanmotors]

Tony,

My Wur # is 0-438-140-069. My car is a 79 row. Im thinking the PO might of replaced the wur at some point.

Won,

Im with jim, what WUR are you talking about?

-Jeff

[boyt911sc]

Originally Posted by Hoffmanmotors

Tony,

My Wur # is 0-438-140-069. My car is a 79 row. Im thinking the PO might of replaced the wur at some point.

Won,

Im with jim, what WUR are you talking about?

-Jeff

Jeff,

I'm not very certain but I found a note that says '79 SC RoW uses WUR (-069). So your WUR is probably correct unless someone with knowledge and experience with this particular model chime in and say otherwise. What particular problem are you experiencing now related to your WUR?

Tony

[Hoffmanmotors]

Well, im not sure even if the WUR is bad or even my problem. I have the engine out to replace head studs and while its waiting for the parts i thought i would clean up the CIS, fix a crack in the airbox, replace vacuum hoses and test the AAR, CSV, and WUR. The car ran OK but i thought it would be a good idea to clean up the CIS while its down, im sure it had a vacuum leak(obviously in the airbox).

I was considering converting it to tbitz EFI due to frustrating tuning with the CIS, but i talked myself out of it and decided to learn more about and keep the CIS. Maybe even become one of the CIS ''Gurus''.

[boyt911sc]

Originally Posted by Won

I can't tell you whether too high or too low a resistance is good or bad, but I can tell you this: inside my WUR, there's the bimetallic strip for the normal WUR function, then there is a second bimetallic strip that is adjustable for open/close position that changes the resistance measured at the plug on the WUR body.

Won,

Is this the type of WUR you were referring? This is WUR (0-438-140-088).



When contact is open, resistance @ 26 ohms. At close position resistance at the plug is 11 ohms.

[Won]

Part number: 0 438 140 090, some say it's for 81-83 SC, others 83 only.

The inside of it:


The second bimetallic strip:


The heating element:


Resistance when heating element is open (cold): 26 ohms
Resistance when heating element is closed (warm): 9 ohms

[Won]

Tony, yep that's the one, except mine's stamped 090 and has a vent connected to the throttle body, I'm not sure if it's before or after the butterfly.

[Jim Williams]

The 090 is used on the '81-'83 US (Lambda) engines. The vent on top is to the atmosphere, i.e., to the connection on the throttle body above the butterfly.

Re the resistance of the heating element: I think the main reason for the difference in the resistance of many of the AARs and WURs for the US versus Euro markets is due to the typical climates -- Colder for the Euro location = longer warmup times.