3.4L swap into a 2.7L -- temp gauge

I have a 2000 Tacoma, originally a 2.7 which overheated and I was able to buy a low-miles truck (2001) with a bad frame for cheap with a good 3.4 and trans. A friend of mine swapped the engine and trans for me, with some small amount of help from me. No easy task. Everything works great except for the temperature gauge, which pegs to hot. If I unplug the sending unit, the gauge goes back down to nil. I've since replaced the sending unit, and the same thing happens. I'm hoping that the temp gauges for the 2000 2.7 and 2001 3.4 are somehow different and I can just replace the gauge itself, but I'm not that optimistic about it. The gauge responding to me unplugging the sending unit suggests to me that the wiring is good and not grounded out, but the gauge worked with the old engine. Any suggestions?

 

Bypass the gauge altogether, it's worthless even on the original engine.

Run monitoring via your OBDII port, assuming everything is wired in correctly.

 

Why do you say that that factory gauge is worthless? I would really like to have the factory gauge work properly; I don't want my truck to end up seeming like a hackjob. Happy to have an additional monitor, but I would regardless want the factory gauge to work right.

 

Because on a completely factory vehicle, you have two monitoring tools.

The gauge communicates via a single wire sender. A bad connection, sender, or broken plug will give you a false reading on your dash. This means your engine can be operating at normal temperature, as well as above or below with no real signs of it if it's not working correctly.

Your PCM communicates via a 2 or 3 wire sensor. This sensor is important as it dictates how your engine is running for instances such as open/closed loop and more. This data is not displayed on your dash as it is independent of it and can only be monitored via OBDII.

 

Those are close enough if the wiring is correct it should work.

The sending unit grounds into the engine .

No tape or non conducting pipe dope .

Sending units are easy to test break out the meter the colder the temperature the higher the resistance .

Don`t burn yourself!

These stock gauges suck when the temperature gauge gets hot most times the damage is done.


All the swaps I do I install a manual gauge .

How did you wire the 4th ECM plug?

Good luck!

 

If the temp sensor is just for the gauge (not the ECU), use the sensor from your old engine (2.7).

 

Senders are for the gauge, and as described above are inaccurate for proper monitoring.

 

The sending unit has a clean connection and if my understanding of the way that these function is correct, the gauge pegging to H indicates too little resistance (respective to temperature), which would respectively indicates that the sending unit does in fact have good ground, just isn't giving the signal that the gauge is expecting. I've tested the sending unit from my 2.7L against the one from my 3.4L (the one in my truck), and they are vastly different resistances at ambient outdoor temperatures (the sending unit from the 3.4L engine was ~640Ω @ ~80°F, the one from the 2.7L was far, far higher). I've been trying to find the specified resistance ranges for these parts but haven't had any luck.

I would happily try to use the temp sending unit from the 2.7L in the 3.4L and see if that would solve my problem, but they have different thread pitches, aaaand now I've broken the sender from the 2.7L engine.

I will certainly install a better gauge as well, but I'll find it very annoying forever to have a dead gauge in the factory cluster.

Unfortunately, I wasn't the one who wired the plugs, that was part of what my friend did with the rest of the engine swap. Unless I'm mistaken, however, it seems to me that the predictable response of the gauge when I unplug/plug in the sending unit would seem to indicate that the wiring from the gauge for the sending unit is continuous and not grounded out. Is there anything in between the sending unit and the gauge? I was under the impression that there was not.

 

I'm also looking at using an OBD connection device to monitor engine temp, just tried to use my friend's maxipro mp808 to confirm that my truck will provide live ect data, but it looks like the tool isn't set up for my truck. Can someone confirm that a 2001 5vz-fe ECU will provide live ect data?

 

Any basic tool that connects via OBDII will read live data.

Why do you think I even suggested it earlier?

 

yes it will !!Only if things are wired correct what response did the OBII device display.

There will be a connector before the gauge. Should be on the right side under the dash

 

Piggybacking off this thread with a similar issue. Factory 3.4, dash gauge reads all the way hot so i replaced the sending unit (at the rear of the motor). When it was unplugged the gauge was dead but after installing the new one it was back to reading full temp again. I'm going to be looking into an OBD2 monitor but like OP I would like the gauge to work as well. I am also sure the motor is not overheating since it does this even when the engine is cold. Thanks