Running a little hot?, I can't tell for sure Options

[RoadGlue]

Howdy!

So we're on our 1200+ road trip in my '74 914 (the blue one!) and she's running a little hot. I can't tell how hot the oil temp is from this gauge though.

(IMG:http://farm3.static.flickr.com/2492/3838520171_8759120d68.jpg)

[detoxcowboy]

Your fine, if the gauge goes higher just back off the engine on the highway or wherever for 5 minutes and it will drop.. ambient temps make a difference.. my 914 runs hotter through L.A. and cools off on the central coast.. which is the route i suggest.. highway 1 is sweet for the 914.... read this it is well informed and will tell you more about the 914 gauge than you will get from here.. oh wait a minute you just got it here.. "the grapEvine is a 914 killer" just kidding .. i used to drag my 1.7 up that hill and decided the 1.7 is not for hill climbing..

THIS INFO> IS DIRECTLY FOR THE 914'S OIL TEMP. FACTORY SET UP.. EVEN USING NOT METRIC GAUGE WIRE WILL SLIGHTLY SCEW THE READING TOO.. DUMMY DUMMY DUMMY GAUGE FOR SHOWING DRASTIC CHANGES NOT COOKING A PRIME RIB..

NUMBER #3 is most pertaining to your situation of judging the gauge.. slow rise time, quick drop time..

Oil Temperature:

The oil is heated by the friction of the contact surfaces within the engine and cooled by the fan directing air through the oil cooler. In order to provide adequate lubrication, the oil must be maintained at a suitable temperature. If it's too low, it will not burn off contaminants that have settled in the crankcase. When the temperature is too high it the oil thins and breaks down becoming a less effective lubricant (it loses its shear strength). The main reason to check your oil temperature is to ensure your oil is not overheating because the stock engine is designed to warm up the oil appropriately. When it does overeat you will also notice an oil pressure loss. This is less of a problem for synthetic oils that can be heated to 300F but pure petroleum based oils have a rated viscosity at 212F and begin to break down at 250F where synthetic oils are still comfortable.

The problem with oil temperature gauge is threefold:

1. The senders are not mounted in an ideal place to take the oil temperature which varies throughout the case. The oil pressure sender is located after the oil cooler so that's not a good place to tee into. Hoover says the best place to mount one is right before the oil pump using the oil gallery plug behind the oil pickup tube. This is because the oil that has just been through the engine and is on its way through again.

Unfortunately this means removing the plug and tapping the case which is beyond the skills of most vw hobbyists. (Factoid: some of the early Type 4 cases had a threaded plug which was removed and replaced with a temp sender on the industrial engines. Most Type 4's do not). Either way, that location is blocked by one of the engine mounts, which would require you to modify the mount as well.

The most popular location on a Type IV engines is the inspection plate cover just to the right of the oil strainer cover (see link at end). Folks drill the plate precisely with a 9/16" bit or weld a nut on the backside for the M14x1.5 oil temp sender.


914 engines had a inspection plate that was designed for this very purpose. VDO sold it at one time as 240 827. The price was $50-60 at the Porsche dealer, somewhat less at your VDO retailer. It's sometimes called the taco plate because of its shape and it replaces the stock plate. The problem with this location is that is still at the corner of the case and does not get a good supply of oil. Therefore the oil temperature is not indicative of temperature of the recirculating oil.

The sender in the photo is the longer style 914 sender. It's designed for a 400F factory gauge and can't be used with the aftermarket VDO gauge. Even with the shorter sender you will find that the dipstick will hit the sender and you will have to file 10mm off the end of your dipstick. Since the dipstick marks are further up, this is a safe modification to make.

These are the various Porsche part numbers involved (courtesy Dave Darling). The items marked in yellow are all that you really need.


Taco plate: 039-101-267
Protective cap: 039-101-275 (wind deflector for cover plate)
O-ring: 021-101-269A
Copper 6mm crush washers: N-013-803-2
Crush washer for sender: 900 123 007 30
Cable holder: 039-101-283
Boot: 311-949-149A
Original 914 sender: 039-919-268
Original 914 gauge: 914 641 118 20
(later version): 914 641 118 30
The VDO part numbers have never changed:

VDO sender: 323 055
VDO gauge: 310 012

Some people like the Berg Dipstick but I think it suffers from the same problems and you lose your oil pressure warning light and the light going on every time the oil temp hits 220F would be annoying. VDO makes a dipstick sender for their gauges but the reading is no better than the sump mounted sender. There is a Type 4 version of this dipstick sender (VDO50003 in the Just Kampers catalog) but be aware it's very long and designed for the 411 engine layout with it's overhead dipstick, unlike the short rearward bus dipstick.

2. If you drill into the inspection plate then the sender will be in the airflow below the engine. Some folks who've found the 914 plate often lack the accompanying cover plate that keeps the airflow from reaching the sender. The result is the same either way: the sender is overcooled and this throws off the reading so you must have a deflection cover in place.

3. The VDO sender has a very slow rise time. Once the oil reaches 250F it may take 3-5 minutes for the gauge to read that value. It's a problem with the sender not the gauge and partly due the fact that the sender is attached to a big piece of metal which acts as a heatsink. When the temperature falls, the gauge responds instantly which is some improvement. This behavior is due to its thermistor based technology. If the senders were thermocouple based the response would be instant but thermocouples have other problems that have to be considered...


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