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'85 b21ft sensors in early b21f block

swedishK

swedishK

Design by Beefsma
Joined
Sep 10, 2008
Location
Soldotna, Alaska
I got a '85 245 turbo for a good deal because #4 punched out both sides of the block. luckily i had a spare b21f block on hand. however, it is an early block, and there aren't enough sensor holes in it. there are two sensor/switches in the FT block that i haven't found a place for yet. the thermal cutout switch for lambda, and the coolant temp sensor for CIS.

so my question is, is there any reason to not run the thermal cut out switch (single prong switch, driver side rear of the motor) in the coolant plug on the forward passenger side? they're the same thread pitch already, which is super convenient.

does anyone have any ideas for the coolant temp sensor for CIS? short of drilling and tapping the block?
 
there are three ports on the head, two in the FT block
the head has (from front to back)
1. wax valve
2. single spade temp gauge sensor
3. two prong thermal timer switch for cold start injector

the block has two
upper: coolant temp sensor for CIS
lower: thermal cutout switch for lambda
 
The system is similar to system used by VW/Audi cars. Maybe something there will give an idea where the sensors can be placed.
 
Volvo had a service bulletin to disconnect the thermal cutout unless the car was located in cold regions. I always noticed it overfueled a cold engine and disconnected the thermal cutout on my 82 turbo and it's been fine. I would still want the coolant sensor in that same area so if there isn't a hole there yet. Time to make one.
 
Thanks, Dave! Well, it does get pretty cold here sometimes. My old '82 turbo didn't have the thermalncut out and seemed to do just fine. Maybe I'll just hook that wire up to the overboost switch?

As far as the temp sensor, what about the coolant petcock port on the passenger side?
 
B21F cars had the constant idling temp sensor over by the thermostat in the head for models so equipped. The intake manifold/Tstat is machined as one flat plane when the head is manufactured new.

Drill and tap for m12x1.5 in the head there?

As to the thermal cutout, that’s more a thing from the days of 1 wire 02 sensors and waiting for them to warm up and/or avoiding a little dip in running as the lambda ecu makes its first “switch”. You decide how important that need is? Though the thermal cutout switch is pipe thread. Early turbo and other k lambda cars the lambda ecu just allows more time before it starts making any meaningful adjustments from 02 feedback, so no thermal cutout.

I’d keep the block drain, it’s really nice to use if coolant /water is used that doesn’t sludge stuff up and clog it..
 
I don't know if the thread pitch is compatible, and if the temperature vs. resistance curves are the same, but the standard LH2.4 coolant temperature sensor has 2 prongs with 2 separate sensors. For LH2.4, one goes to the ECU and one to the EZK. If the threads match, you could try measuring resistance of 1 prong K-Jet vs. 2 prong LH2.4. Try room temp, freezing, and boiling.
 
Kjets On a Plane said:
B21F cars had the constant idling temp sensor over by the thermostat in the head for models so equipped. The intake manifold/Tstat is machined as one flat plane when the head is manufactured new.

Drill and tap for m12x1.5 in the head there?

As to the thermal cutout, that?s more a thing from the days of 1 wire 02 sensors and waiting for them to warm up and/or avoiding a little dip in running as the lambda ecu makes its first ?switch?. You decide how important that need is? Though the thermal cutout switch is pipe thread. Early turbo and other k lambda cars the lambda ecu just allows more time before it starts making any meaningful adjustments from 02 feedback, so no thermal cutout.

I?d keep the block drain, it?s really nice to use if coolant /water is used that doesn?t sludge stuff up and clog it..
Click to expand...

Good to know! Would converting to a heated o2 sensor negate the "need" for the cutout?
 
Install the coolant temperature sensor next to the #1 intake port on the head. The thermal cutout switch doesn't really do much, except to keep the engine in open-loop longer when cold. It'll run fine without that connected. Both my '82 and my '85 are set up like an '81 Turbo without the switch plugged in.

With respect to a 3-wire sensor, yeah, it'll help, but probably only when the temperatures are really cold. When its 25-30 deg F, the car should run fine with the 1-wire sensor. Just wait until the engine stops doing its mood swing thing when warming up before you pull out into traffic. You'll need to wire the heating element up, since the turbo cars didn't have the necessary circuitry to run it.

-J
 
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You shouldn't need a heated o2 sensor if your 240 turbo has a stock manifold with the o2 in the stock location. That's about the hottest spot they could have put it in. lol.
 
It'll probably be ok. It's still very close to the turdblow. I ran a single wire sensor on our old 744Ti when the original 3-wire unit finally failed. Worked fine. Just had a little bit of a hunting idle when the computer first started sampling the O2 sensor signal. Stabilized within 3-4 seconds, though. When I installed a B23FT in that car, the turbo I used was on a 240 manifold. So, I had a choice between the two sensors. Didn't really matter which one was plugged in. Same response.

My 245, when it had the old B21FT in it with the 740 exhaust manifold, had the sensor in the downpipe. Didn't run any differently than it does today with everything in the stock location, other than the fact that the old fuel distributor was quite gummy inside.

-J
 
I run the o2 sensor in the vertical part of the downpipe. Using a 90+ manifold. too. The single wire o2 works fine in that location and I have easily passed emission checks. Ideally a heated one in that position should be a bit better. But it was all working and happy and I monitor it with another wideband in that pipe going to an LM-1.
 
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