tempest411

Hello,

I've got a late block which I'll be eventually installing into an early chassis, and the senders for the dash gauge are a different thread size. I can make an adapter up easily enough so the early (M10x1.0) sender fits in the hole of the late block (M14x1.5), but I got wondering if I can just get a late sender, as according to Clarks's, they are virtually the same as far as their change in resistance across the temperature scale. See: https://www.google.com/url?sa=t&rct=...99804247,d.cGU I can also add an LED as a warning light as long as there is a switch built into the late one. I added this to the ammeter in my old Ford truck (a low-voltage warning circuit triggering an LED carefully incorporated into the original ammeter). Would this work?

Thank you for your advice,

Rick

Ish_944

I've checked your link but it says nothing on the same voltage range of the temp sensors. Are you sure about this?

Anyhow, we used an adapter. Figured that it can't hurt to match the gauge.

Edit: One more thing to consider is: afaik, the early unit is not in actual contact with the coolant but is located in a blind hole on the engine. The later one is protruding into the coolant. (If I understood my mechanic right, gonna check tomorrow in person.)

tempest411

Clark's lists the change in resistance for the senders at a given temperature, and though the chart listed doesn't provide a 1:1 equivalency, I'd say it's so close as not to matter based on my experience looking at sender specs for other applications. In fact, I'd bet the later sender is an exact match electrically, with the differences being physical size, and the late one having a provision for a warning light.

odonnell

There may be an issue with making an adaptor, the sensors are probably calibrated differently (early sensor not touching coolant). If you put both senders in a pan of boiling water, the resistance curves may not match. But when installed, the apparent temperatures will be close enough that they will match. The discrepancy (if there is one) is because of the different heat transfer properties of the installations.

The safe thing to do would be to retain the late sender and just wire it for the early application.

V2Rocket

My early car came with the late style sensor from the factory.
I suspect there's not enough of a difference to matter...or you may just need to swap the multi-gauge.

konakat

Yeah, that chart makes it look like they are intended to be equivalent, but Porsche probably published a more detailed spec later for their suppliers to meet. The injectors are the same way between early and late. The same part, but the spec is written differently. I wouldn't try to use an early sender since it may not be designed to be in direct contact with the coolant.

Tiger03447

My early block has the sender going into a blind hole..I just replaced it the other day with a new one. I presume that once the block gets warmed up enough, the entire mass is at the same temp...Seems that the water contact temp sender would react more quickly than the one in the blind hole. I suspect that the block thickness at the back of the blind hole is pretty thin and backs up against the water jacket...I wonder how many iterations of machining the hole depth, it took Porsche to get the right readings...fairly quickly...

odonnell

On my early car, it seems to respond fairly quickly despite the blind hole. For example last week I was driving hard in 100* weather and stopped at the store for 5 minutes. When I came back out the gauge was at the halfway point, it was just above the first hash mark when I turned off the engine. Within 5-10 secs of the engine being restarted the temps were back down to almost the first hash mark.

konakat

The aluminum block is going to help a lot with the responsiveness of the gauge. Aluminum conducts temperature quickly and efficiently.

FRporscheman

I started a thread just like this last month. Except I have an early block going into a late car (rebuilt an '87 engine using an '84 block).

What I learned is that the sensors are cross-compatible, except for the thread size, and that the later one has an integrated warning switch. So in my case, I have to use the M10x1 single-pole sensor, and find a way of rigging a warning switch for the dash's idiot light. In your case, yes, just use the late sensor, and use only 1 pole (for the gauge) or go ahead and install an LED somewhere.

FRporscheman

..

tempest411

I ordered the late sending unit earlier tonight. When it comes I can test them side by side in some water on the stove with a meter, just to see how close they are to one another.

Out of curiosity, I know the late sensor has a wide and a narrow contact. Which one is for the gauge, and which one is for the light? Edit: I suppose the one with the 'open' reading would be for the light, yes?

Thank you!

FRporscheman

I think the narrow post is for the light, but like you said, you can confirm.