Where to tap in Coolant System for Gauge

[Doakster]

One last suggestion... because of the design of the VW cooling system the rad hoses are the last things to heat up and by definition will run cooler than the rest of the engine.. the head circulation circuit is probably a much more accurate place to find out how hot the engine is actually getting.

If i do tap into, cut or splice the radiator hose, it will be as close to the front head port as possible.

[Doakster]

Let me clarify something, just took another look.

My front head outlet, has 3 ports, two for sensors, and one that goes to my oil cooler

My driver side head outlet has 2 ports, one that goes to the heater and one for a sensor.

I'm thinking the easiest way would be with a splice on the upper radiator hose close to the head. I measure the outside diameter of hose and it's just under 1.5in. If i can find a splice that is 1.0-1.25 internal diameter that would probably work.

[Doakster]

I think this one should work great, if the OD of the coolant hose is 1.5, the ID should be 1-1 1/4in, so this would should work great.

http://www.autometer.com/cat_accessoriesdetail.aspx?vid=51

[Vincent Waldon]

Probably didn't state this clearly enough in my post... the "ports" I'm referring to are specifically for coolant temp sensors... ie a "dual port" has two ports for coolant sensors plus the actual outlet... three outlets in total.

There are two sensor  (dual port) versions of the driver's side flange as well... but if you're not worried about cutting and splicing your plan will work fine as well.

[Doakster]

Actually if i could do a dual port on the driver side some what easily than i would prefer to do that. My flange is actually slightly leaking so it needs to come out.

The only think i'm worried about is going from the sensor port to an NPT aftermarket temp sender, i don't see how that is going to work. Correct me if i'm wrong but the port is much larger and normally seals through an o-ring on the VW sensor and a retaining click. Not seeing how i could make the adaptation from the large port to NPT.

The splicing just seems real easy, just have to find the right size internal diameter splice piece.

[92EcoDiesel Jetta]

Why do you need another temp gauge if I may ask? What's the matter with the OEM temp gauge?

[Vincent Waldon]

There's two versions of coolant ports... the cartridge type you describe (that seals with an o-ring and a spring clip) and an earlier version that's straight hole tapped M10x1.

This guy actually sold me a brass adapter for the cartridge-type, although I think he's stopped making 'em:

http://www.toywagen.com/

He might still have one kicking around, if the cartridge version is all you can find.

Otherwise you can drill and tap the M10x1 version (part numbers I mention) for whatever your coolant sensor is... IIRC M10x1 is very very close to 1/8" NPT as is... within range of some teflon tape perhaps.

[maxfax]

Why do you need another temp gauge if I may ask? What's the matter with the OEM temp gauge?

Generally OEM gauges are not terribly accurate..  Especially with 15+ years under their belt..

 On alot of manufactuers the OEM gauges are merely about as effective as an idiot light..   THey don;t show an accurate representation of what is going on but rather the extemes either way...  THe idea behind this was to keep you out of the dealer's hair for warrenty work unless there was a major issue.. 

[92EcoDiesel Jetta]

When you say OEM gauges are not accurate, do you mean they are not marked with numbers in F or C? Or do you mean the gauge does not go to the same spot for the same temp from day to day? If it goes to the same spot for the same temp, then it is accurate, just not calibrated. It can be easily calibrated with an ohmeter, pot of boiling water and an accurate thermometer. The temp sensor is a variable resistor- rugged and reliable, the gauge is just a meter movement, also rugged and reliable. Sender + gauge is a very simple circuit. As long as it has a good ground and wiring, I don't see why it is not accurate.

[maxfax]

A tad of both I suppose..     Alot of it comes down to quality..   Yes in theory it is a rugged and reliable deisgn, but after the bean counters were done with it it becomes "on a budget and adequate"..  A decent aftermarket gauge is generally going to be of better quality and accuracy... 

I have an aftermarket electric gauge in my car..  And I still have the OEM gauge working too..   I can say that it doesn;t really appear to fluctuate , however I'm not real keen on it's movements.. And it's a cheap, aging gauge...
 The aftermarket gauge responds MUCH quicker if/when something happens..  The range is much easier to determin on the aftermarket gauge too..  On my one particular car from 195 deg F - 240 deg F it moves almost 2 notches..  Makes it rather difficult to tell if it is at 215 and I'm still okay, or 230 and I should be shutting down..   It is a 29 years old, I coudl spend an afternoon cleaning connections, replacing wires/senders/voltage regulators and possibly get it working better for a while..   Or spend a half hour and $20 on an upgrade....

[Vincent Waldon]

As always, it's really a  matter of personal preference.

I have both the OEM dash gauge and a VDO aftermarket water temp gauge on my MK3 IDI.  Compared to the VDO aftermarket gauge (which I've calibrated in boiling water, adjusting for Edmonton's altitude  ) the OEM dash gauge is both inaccurate (not calibrated correctly) and very heavily damped... ie... it lags way behind actual changes in engine temperature.  I'm not surprised... the OEM part is designed to be a general and inexpensive indication of engine temperature and is backed up with a flashing red light should actual overheating occur.. so for the average driver more than enough info.  I just like more info than the average driver.... in particular... during spirited driving or a big hill I like to see the upward trend in coolant temp and turn on the rad fan manually to get ahead of the thermal curve.

I also have both gauges on my MK4 TDI.  On the TDI the OEM gauge is deliberately stunted... it goes to 90C and then sits there, regardless of actual coolant temp, unless an overheat actually happens, in which case it suddenly swings all the way to red.  The general concensis is that VW did this because too many folks were calling the dealers with service concerns as the engine cycled thru the normal temp swing the more thermally efficient TDI design does during normal driving.  My aftermarket gauge is very sensitive... I can tell within 5 seconds if my foot is on the throttle or not.

I'm told many many Ford temp gauges are completely binary... the sensor is just a switch and the gauge either reads cold or normal.  Same idea... the average driver just needs to know if there's a problem... OEM gauges market better than idiot lights.

Stock gauges are just that... and in general fine for knowing if your engine is in trouble or not... and for the vast majority of folks enough info.  Some geeks just can't get enough data, however... 

[maxfax]

Dampened was the word I was looking for..  Yes severely dampened..

I'm told many many Ford temp gauges are completely binary... the sensor is just a switch and the gauge either reads cold or normal. 

Ford was/is notorius for this on oil pressure and temp gauges throughout the ages..  Low, Normal, and High is all they will read...  Newer GM products are exactly the same..   The sad part is late model GM's gauges get their signal from the ECM which is getting it's reading from a highly accurate sensor..