Cylinder Head Temp Sensor re-mounting
 

The PO of my 914 had somehow destroyed the cylinder head temp sensor and drilled out what remained of a broken one and made a big hole that is maybe half an inch in diameter. SO in order to put a new sensor on there, he epoxied it in place. Most epoxies are good electrical insulators, so he fashioned an extremely crude ground wire. Its amazing how people can mess up cars, but the way people mess up a wiring harness or do electrical work is beyond me.

So anyway, I need some advice on how to mount a new sensor in this hole. I dremeled out all the epoxy and the hole is nice and clean.

I've got a couple ideas but I don't know if they will work...

1. Use silver loaded epoxy and do the same as the PO. - advantage is that silver epoxy is a superb electrical and thermal conductor - disadvantage may be (don't know) that the epoxy may become molten when the engine is hot on a hot day. Its possible that the PO used a high temp epoxy...

2. drill and tap a hole somewhere else on the head - I'm not really sure where this could/should be done, and I'm afraid of drilling all the way through into the combustion chamber.

Any other suggestions? (other than get a new head, this is a 1.8 after all :) )

-Tony

I'm not sure they're any better, but--

Timesert the hole in the head. You may be able to get a large enough OD one that it will work well.

Drill the other head and tap the hole and put the sensor in there. You'll also have to cut a hole in the engine tin and run a wire.

Locate a Bus (?) part that allows you to put the sensor into a fitting you screw into an engine tin hole.

...Those are all the ones I can think of off the top of my head.

Check the silver-loaded epoxy; if it's good and stable up to 450-500F, it'll work at the CHT location. That part of the head shouldn't get to 500F. And if it does, you'll have a lot more things to worry about than the fuel mixture...

--DD

Unfortunately the hole is far from round. its sort of shaped like a nuber 8.. a bi-modal hole if you will :)

I like the idea of doing the other head. I'll take a look and see what I can do. Still a bit afraid of drilling into a head :)

-Tony

Looks like the highest temp nickel based conductive epoxy will only handle up to 400 F I guess I'd better find another solution.

-Tony

Weld up the hole in the head, in the car, drill and tap to correct size.

Niether of my heads have a temp sensor. Where the standard on all teeners. If some one has a pic I would love to see it.

Old school JB weld.

You can fill the hole and then retap the hole if you use JB.

If your car still has fuel injection, it does have a temp sensor. Not one that will run a CHT gauge, but there is a thermistor. Look for an extra hole in the engine tin over by the #3 spark plug hole. The CHT sensor is accessed through that hole. It's a pain to get to...

--DD

The problem with JB weld is that it is not electrically conductive. It appears that the PO did just this thing and its not a reliable way to go, because you have to make an electrical ground from the case of the sender to the chassis ground of the car. Also, I wonder how good an insulator JB weld is, and whether this would effect the ability of the sensor to function properly.

If I could come up with a good way to ground the case of the sensor the JB weld is a nice easy idea.


Otto: I don't have a welder so that makes it a bit tough... And unless its very cheap to have someone do that, I'm inclined to find another solutions first. I don't really plan on keeping this engine long so I just want to get it running reasonably well. But I think that solutions is really the ideal way to go.

-Tony

The right answer.

1.8 heads should be cheap enough to buy another one. of course, buy the side that has the fitting for the CHT. 1.8 should be basically a bus head

Here's a trick my PO did on my old heads (I'm not using them any more for a different reason). He enlarged and tapped the hole the sheet metal attaches too right above the hole for the temp sensor. You will need to bend your sheet metal a bit, but shouldn't be too big of a deal, and it seemed to work ok on mine (even though it is/was a hack job)

-Kevin

My cylinder head has an opening for the head temp sw to screw in. Is there a kit with gauge and switch?

Nope. The sensor the FI uses is different from the one that the gauge uses. They are not compatible.

You can use the stock CHT sensor to work a stock oil temp gauge, however. I'm not sure how much the needle will move, but they work on the same principle and you probably will get some sort of "warmer" or "cooler" reading, just like with the stock non-numbered oil temp gauge.

--DD

Those are really great ideas, but if you are in a pinch and wont keep the car long, how about also just getting a potentiometer of the correct value and inserting it into the circuit. Manual CHT sort of...you could even run it into the cockpit.

Hehe, I like the idea of the potentiometer :D Or, I could hook up a pyrometer looking through a hole in the engine tin and use a digitally controlled potentiometer (digipot) in the FI circuit.

I think though I will probably just epoxy it in with JB Weld and make a better electrical ground. I'm also going to investigate the idea of using one of the mounting holes by re-drilling and tapping it. I hate doing horrible things like this to cars, I feel like I belong in the "putting holes in the door panels for speakers" crowd.

Oh well.

-Tony

chts
 

What is the best way to replace this sensor and what should i watch out for ?

If possible could someone show a pic of the location ?

Thanks.....

soak overnight with penatrating oil. if the sendor is stuck, and you wrench on it hard, it can shear off, leaving the threads in the head. so go gentle on it

Actually, the soft aluminum threads in the head come out on the sender. That's worse, IMHO, than leaving the sender's threads in the head.

Penetrating oil, maybe heat, and hope are all I can advise.

--DD

Sears has a ratchet that is hollow, makes removal and install very easy. Run the sensor wire up through the ratchet.