Open Road

I noticed that the coolant pressure switch on my 86.5 (928 641 513 00) is starting to leak. I did a little research and found that a replacement is silly expensive (~$170) for a what it is. However, I also saw a few threads where people said to just remove the switch because it has little to no use.

Is this correct? Is the switch's job to detect when the reservoir has been opened and the system depressurized, which then turns a low coolant light off under the assumption that since the system is depressurized that someone opened the reservoir and added coolant? That seems byzantine even by German engineering standards.

If this is true, two questions: 1) Is it better to just replace tat entire hose or to splice in a coupler where the switch was? 2) What to do with the switch's electrical connector? Tape it off and tuck it out of the way?

Thanks,
Matt

Porsche actually makes a “pressure sender delete” part. It’s a double-ended barbed coupler (1/4” IIRC) exactly like you can get at a hardware store (ask me how I know) except that it’s untreated steel, rather than brass (which is what you get at the hardware store.) And the h/w store part is much cheaper.

Do that -^

I can neither confirm nor deny the correctness of your statement of theory of operation: many, many years ago I studied it and at the end thought “that’s some German over-engineered shit” and promptly forgot it except for the “delete” part. As far as I am concerned its primary purpose is to spring a hard-to-find vapor leak after 20 years.

Tuck the connector out of the way. Zip-tie it if you want.

You had me at delete. If it means simplifying things, all the better. I'll head over to my trusty Ace hardware, which seems to have every fitting I need somewhere, and get rid of the leaky switch.

Thanks!
Matt

I deleted the coolant pressure switch today.

I used a 5/16" brass barbed splicer with a new 4-5" section of 5/16" ID heater hose from the old switch location to the coolant reservoir. I think this small section had been replaced before because the hose I replaced looked newer and was Continental, not Porsche labeled.

I had to remove a hose bracket/fender bolt to move one hose out and access the subject hose under the fender. And I had to be careful to make sure I installed it with the same run behind wires, other hoses, etc. In other words, typical fiddliness.

The 5/16" splicer was a little harder to find than 1/4", but it more closely matched the ID of the factory hose and the nipple on the reservoir. The challenge was that the old clamps are a tight fit over the new hose once the splicer is inserted. They do fit and clamp, but make it a little harder working the hose over the barbs and reservoir nipple (Particularly the reservoir nipple because i am terrified of putting too much or wrong-angled pressure on that pricey piece of plastic).

The connections on the old pressure switch which I removed are 1/4" diameter, so a 1/4" splicer should work fine too, as long as you snug up the clamps.

Excluding trips to find the splicer and buy hose, it's a 60-75 minute job with generous opportunities to cut your hands and arms on the edge of the fender, the VIN plate, and various screws and clamps.

Addlight wrote: ↑Wed May 21, 2025 5:19 pm ... it's a 60-75 minute job with generous opportunities to cut your hands and arms on the edge of the fender, the VIN plate, and various screws and clamps.

Yup. A very uncomfortable job. Unless the motor's out and you can sit on the engine carrier.

I've beed deleting the pressure switch on every motor-out service. This avoids the question of "Well, why didn't you do that when it was easy?" when the switch inevitably springs a vapor leak.

The other thing: I cannot remember anyone, ever, reporting that that sender flagged the failure mode it's designed to detect.

this is an interesting thread. I've never heard of this switch before, and I'm sure I've seen it as one of those many things under the hood that I just ignore because I don't (yet) need to know about it (now I've jinxed myself). Anyone have a pic of it?

linderpat wrote: ↑Fri May 23, 2025 7:08 am this is an interesting thread. I've never heard of this switch before, and I'm sure I've seen it as one of those many things under the hood that I just ignore because I don't (yet) need to know about it (now I've jinxed myself). Anyone have a pic of it?

I happen to have a freshly deleted one right here. The switch's total length is about three inches. (I mangled one of the switch's ends prying the old hose off of it.)

The likely reason people aren't aware of it is because it resides behind the washer fluid filler neck and under the inner fender. In the picture, the short hose is what attached it to a nipple on the reservoir, so that is its distance forward from the reservoir. There are two nipples on the reservoir, one for the return hose, and the one for this, which is the one farther inside the fender.

From this switch, a hose is routed along the fender and then across the top of the radiator to a connector on the top of its driver side.

Probably some Sr. Engineer somewhere who's first assignment was to solve whatever issue that sensor was supposed to address.

worf wrote: ↑Wed May 21, 2025 6:01 pm The other thing: I cannot remember anyone, ever, reporting that that sender flagged the failure mode it's designed to detect.

has anybody joined the wires on the connector together to see what, if anything happens ?
might try it on mine tomorrow.
cheers
Phil

h2pmr wrote: ↑Fri May 23, 2025 4:14 pm has anybody joined the wires on the connector together to see what, if anything happens ?

Probably. Report back what you find.

More interesting would be to do some black box testing of the sender.

had a look into the operation of the pressure switch today.
tested on an early'ish RHD 87 model, its got a folding rear spoiler
all coolant functions work just as they should + cooling flaps prior to doing the test.

pictured is its position on a RHD, so easy enough to get to, wiring connector points down in fitment



i removed the switch and connector, which looked in pretty good shape, and fitted 2 long lengths of wire to the 2 wires going to the switch


started it and left it ticking over with the wires disconnected, and as everybody who has disconnected theirs knows, all works just as it should.
then i joined the wires together and watched the operation of the fans and cooling flaps and again all worked as it should
then went to look at the dash and the coolant and main red ! light were on


when i disconnected the wires both lights stayed on, i left it ticking over for a couple of mins and they did not go out.
switching the ignition off and started it up again with the wires disconnected and the lights did not come back on again.

so with it ticking over i sat in the drivers seat, joined the wires together and watched the dash, after exactly 20 seconds of the wires being joined, it brought both lights on.
must be to stop sudden quick fluctuations of the pressure from bringing the light on.

and if get these lights on the dash and you unplug the connector while its still running, the lights will stay on, so could cause confusion and think its not the switch thats at fault, as you need to switch off the ignition to get the light to go out.

then i did a basic test on the switch, using a mitivac to create pressure, putting my finger over the end of the switch>
at rest its as pictured, switch is open.
putting pressure in to the switch, the resistance falls, very approx 5psi was 100k ohms, but no idea how good the switch is or at what resistance it triggers the warning light


hope this helps someone some day.
cheers
Phil

h2pmr wrote: ↑Sat May 24, 2025 10:04 am then i did a basic test on the switch, using a mitivac to create pressure, putting my finger over the end of the switch>
at rest its as pictured, switch is open.
putting pressure in to the switch, the resistance falls, very approx 5psi was 100k ohms, but no idea how good the switch is or at what resistance it triggers the warning light

The mitivac is switchable between vacuum and pressure?

worf wrote: ↑Sat May 24, 2025 12:59 pm

h2pmr wrote: ↑Sat May 24, 2025 10:04 am then i did a basic test on the switch, using a mitivac to create pressure, putting my finger over the end of the switch>
at rest its as pictured, switch is open.
putting pressure in to the switch, the resistance falls, very approx 5psi was 100k ohms, but no idea how good the switch is or at what resistance it triggers the warning light

The mitivac is switchable between vacuum and pressure?

yes, but i think only the second time i have used it on pressure.
cheers
Phil