New coolant temp sending unit is too big...but have an idea.
 

Hey guys! The water tempature sending unit on the engine block on my early 944 has a pretty shallow hole that it's saposed to go into, and is a single prong design. Since I installed a post 85.5 wiring harness, this connector now uses a two prong design and the new unit itself is much longer, and will not fit the current hole on the block.

I was wondering if I need to drill into the block to accomadate for this extra length? If I do this, I'm pretty sure that the sensor will be in the water jacket itself, probably giving me a better reading. Is this how the late 944 was done?

Thanks for any help!

-Tony

NO, NO, NO! One connector is for the temperature sensor and one is for an idiot light in the late model gage cluster. To figure out which one is which, turn the ignition on and ground one lead at a time. When the temp gage pegs high you just found the correct lead. Connect that lead to the original temp sensor and you should be good to go.

The late model sensors are longer because they penetrate into the water jacket, where as the early sensors do not.

BTW: I hope you didn't swap the harness just to install the '87 DME and AFM. If you did, then you wasted your time. My '84 is running a DME and AFM from an '86 using the stock '84 harness. The only thing I "loose" is the idle stabilizer, but who cares?

Not only would you have to drill the hole deeper but you will have to drill and tap the hole larger. Tapered pipe type threads I think.

As Cliff has stated you didn't need to change the harness for the newer DME and AFS.

In fact you may find the instrument end of the harness totally uncompatable.

The "newer" gauge temp sender had two pins, one for the gauge and one for the warnging light -- which the early 944's do not have. The one for the gauge has the same resistance as the early single pin senders.

Maybe I wasen't quite clear. I DID need to change the engine wiring harness as the engine (early 944) is now in an '87S body. The instruments and relay box required the new harness.

I've switched out all the old sensors with post 85.5NA one where needed (even replaced the aux. air valve with the idle position sensor) so it's basicly now similair to a post 85.5 944 design, except for this hole that the sensor is sapose to go into.

Drilling and tapping it would be no problem, I'm just wondering if this is how it was done on later models for some reason. So in effect, you've answered my question and given me a good idea why my (!) idiot light is on! =)

Is the water jacket the same size on the early 944 as the late 944? Will it accomadate the larger sensor? If so, I'll be out driving this weekend! =)

Thanks guys!

-Tony

That's a tough call. The sensors are in about the same place on the early and late engines, but I'm not sure about drilling and tapping the hole.

One major problem that I see is what happens to the metal chips that fall into the water jacket? If you had the head off it would not be a problem, but this sounds way to risky. I'd stay with the early sensor and remove the blub for the idiot light.

Just my $.02.

BTW: What size tap am I going to need to thred this larger hole?

-Tony

As far as the shavings, I'm drilling VERY little at a time, and vacuuming the bits of metal out. There's still going to be a very minimal amount of metal in the system, so I'm going to disconnect the upper radiator hose and flush water through the system to get the remaining crap out of there. This way the shavings don't get into the radiator or water pump, which is what I'm mostly concerned about.

Thanks for the help!

-Tony

I'd put the right early sensor in it.

btw...my 'early' 85 had the 'late' sensor (original engine since new) so there were some early cars that started to get 'late' blocks I guess...my sensor had the extra connector for the warning light but no matching harness plug...of course this is nothing unusual for Porsche to do is it?

That's pretty weird, Tom. I would really like to use the new sensor, because maybe one day I might need that idiot light. Not only that, but I've come this far, and paid so much attention to the little details in doing this engine swap, that I would feel bad if I didn't go all the way.

But let's say I do use the old sensor... What can I hook the idiot light up to so that it won't interfere with the other sensors that use it?

Thanks for the quick responces!

-Tony

I does nothing but supply a ground to a bulb in the instrument cluster (IIRC)...how old is the water pump?...new style?

Use the single pin temp sender as you may not be able to find the right tap for the threads on the newer sensor.

You can splice into the correct wire behind the plug and use the older slip on connector. Yes the older connector as this is a special slip on designed just for the flat head on the early temp sender. But the wire does corrode behind the special connector so solder in new wire.

You are going to use the DME from a post 85.5 944 NA right? The brain for the "S" is not compatable. As well as the AFS and the idle control valve and the use of a seperate speed and referance sensor. The "S" models use one with a special flywheel. Trick but not compatable.

Tom, thanks for the info. It is a new water pump. So I could just go ahead and ground the other wire to the block and all will be well? I think I remember hearing that's how the original sensor worked, but they switched to the current design because of the corrosion problem...

SoCal, the post 85.5 DME and AFM I have installed are from an '87NA. The reference sensors and flywheel are from my early 944. Everything is working fine. The car actually runs! This is the last hurdle in getting my mixbred car on the road! =)

Thanks very much guys!

-Tony

use the 'early' temp sensor...do nothing with 'late' engine harness idiot light wire (tape it up - if it touches a ground it will light up the temp idiot light)

most problems with overheating were because of the early water pump

I have a 'late' sensor that I could hook up to the horn I guess ! ...but I have a new, improved water pump and I watch the gauges often enough that I'm not going to worry about it.

Yes it's always those little things that can jam the works.

Interesting project. Best way to save an "S" model.

drill and tap it, std. metric thread, you'll know once you're through, no need to go any further(cyl. walls!), I've done it on a few blocks for the exact reason you mention, early motor in late car. M14 off the top of my head, if I have some extra time I'll check. don't worry about the job, as you said, go slow, use a vacuum,

Cliff,

what exactly is the idle stabalizer?

thanks

The idle stabilizer is a motor operated "throttle valve" that takes the place of the Auxiliary Air Valve and the A/C supplementary air solenoid.

On the early cars the AAR is used as part of idle and mixture control during warm-up. When the engine is first started the AAR is fully open to allow additional air to flow into the intake tract. The AAR uses a bi-metallic (temperature sensitive) device to control how far the valve is open. As the engine comes up to temperature the AAR closes. When the AAR is fully closed engine idle is controller by the idle by-pass on the throttle body. When the A/C is running the A/C solenoid opens and allows additional air to flow into the intake to compensate for the additional mechanical load.

On the later cars the AAR and A/C solenoid were replaced by the Idle Stabilizer. This device is controlled by the DME. When the DME sees a change in RPM (at idle) a signal is sent from the DME to the IS.

Thank you all for the great info! I will be drilling and tapping it this weekend. (Come this far already, so why not?) With any luck, I'll be out, eating the mean streets of St. Louis by Sunday!

Thanks!

-Tony

cliff,

thanks for info on AAR & idle stabilization

To suppliment: The idle bypass valve on the pre 85.5's is heated with a 12 volts from the same circuit that powers the fuel pump. There is no DME control other than the closing of the stage two contacts in the DME relay.

The post 85.5's have a single sided servo design. The DME pulses the valve against a return spring. The width (duration time) of the pulse dictates the closing amount.

The 944S and possibly the 968 use a true servo valve where the valve is driven both ways by the DME and not spring loaded to stay open. So the voltage/current can be turned off to the valve if the possition is acceptable for up to temp running.

This is why you have to jumper two of the pins on the test connector in the engine compartment to set the idle on the post 85.5 cars.