Adding New Gauges to '89 Chevy 454

[engineer bill]

The tiny OEM gauges in my dashboard gauge cluster work, mostly-sometimes intermittantly, but I want to add some aftermarket gauges for Oil Pressure, Oil Temperature and Transmission Temperature. I bought the new gauges, and the sensors are electric and each has a 1/8 NPT connection. I need to figure out where to install each sensor. Also, I would prefer to keep the original dash gauges and sensor working, just for old times sake. Is there information out there that that would help me find appropriate ports? Any input would be helpful.

[Rickf1985]

I was thinking the same thing, check this out.
http://www.classicwinnebagos.com/forum/index.php/topic,10012.0.html

[DaveVA78Chieftain]

If you want to maintain operation of the original gauges then you will have to install brass "T" fittings so you can tap the new sensors in.

Oil pressure and oil temp:  This thread provides the existing oil pressure circuit.  The large sensor is used for the dash guage.  The small sensor MJ replaced is a combination idiot light and fuel pump safety switch.
http://www.classicwinnebagos.com/forum/index.php/topic,6609.0.html

Tranny Temp: I believe many install the sensor in the fluid pressure port.  Refer to page 7A-14 of the 1988 GMC Light Truck Service Manual in the Free Manuals area for the location of the fluid pressure port.

Dave

[cncsparky]

For tranny temp, I had a bung welded in the stock pan. 

Actually, bought two of these and had them welded in. One for drain and the other for the sensor.

http://www.summitracing.com/parts/bmm-80250

You can buy aftermarket pans with sensor ports already in them.

[Rickf1985]

The temperature of the oil in the bottom of the pan is substantially cooler than the oil running through the transmission. The oil in the bottom of the pan is basically reserve oil and does not really circulate through the transmission. It will pick up heat from the return oil but heat rises so the hot oil stays at the top of the oil level. This has been tested many times in real world testing. The best place to test the transmission temp is the cooler line leading to the cooler. That is where you have access to the hottest oil in the transmission, at least the hottest you can get to. It is a few degrees hotter at the torque during acceleration before lockup but there is not way to access that.

[cncsparky]

The OEM transmission temp sensor in a 4L80E is on the valve body, ie measures pan temperature  .  If the factory does it there, good enough for me.
Average temperature of the pan after the cooler has done its job is more useful to me.  Seeing temporary temperature spikes in the cooler line tells me nothing.

I'm still trying to process this statement: "The oil in the bottom of the pan is basically reserve oil and does not really circulate through the transmission."
So the oil in the bottom of the engine pan is also 'reserve' oil?  Must be why it is nice and clean when drained out  D:oH! .

The fact is that tranny fluid is constantly being recirculated throughout the transmission.  Fluid from the cooler is dumped back to the pan and it does not segregate itself to the top of the pan.  I imagine it is completely mixed with existing fluid in there. 

[Rickf1985]

You could be right, I have only been building and racing them for 40 years, not all that much experience. I do suggest you pull up a chart of the oil circuit of your tranny. The hottest oil is at the converter and that is what you need to know. Oil breaks down with heat, knowing what the temp of it is after it is cooled does no good at all. I can point out a dozen things the factory has done that make no sense at all and some are downright dangerous. The factory does things in the name of saving money, not accuracy.

[cncsparky]

Well aware that the convertor builds heat.  So what is your opinion when fluid is too hot?  Too hot, for how long?  Do you agree that temperatures above 220 deg(commonly accepted) are probably bad for the fluid?

If you see a temperature spike above 240 deg pulling a hill, is the fluid now bad?  Do you change the fluid?  Put a bigger cooler on it?

[engineer bill]

I see from reading this topic that there are several schools of thought about setting up a transmission temperature sender.

So, just thinking about it so don't jump all over me ... If I were going to tap into the transmission hot fluid line to the cooler, where would be a good place to do it? Is there a fitting kit for this? Any thoughts about that?

BTW, my excursion under the winne yesterday confirmed that my transmission is a TMH400. As near as I can tell, it is not easy to swap in the other transmission referred to in my service manual.

[cncsparky]

Bill, you can get sending unit manifolds that tap into the cooler line. 

Like this:
http://www.summitracing.com/parts/dak-sen-04-11/overview/

It is probably one of my primary reasons for not going this route.  The manifold is somewhat expensive, and the compression fittings is another point that could leak.  I also didn't like the idea of cutting into my cooler lines. 

The alternative is to install a bung into the pan (what I did).  I had mine welded and can be used as a drain if wanted.  There are also aftermarket deep pans with the fittings already installed. 

[Rickf1985]

Well aware that the convertor builds heat.  So what is your opinion when fluid is too hot?  Too hot, for how long?  Do you agree that temperatures above 220 deg(commonly accepted) are probably bad for the fluid?

If you see a temperature spike above 240 deg pulling a hill, is the fluid now bad?  Do you change the fluid?  Put a bigger cooler on it?

Sir, You are trying to drag me into an argument and I am not going to let that happen. Google Transmission temperatures and you may find the answers you are looking for.

I am going to back out of this thread, I made a promise to Mark a long time ago that I would not let my expertise start arguments.

Bill, There are cheaper ways to tap the tranny line, ask around.

[cncsparky]

Rick, I am not trying to argue with you.  Sorry if I sounded that way.  When someone tells me the 'best' way to do something, I would like it backed up.  Show me why its the best way.  Too many keyboard experts on the net to take advice at face value.

I've been searching for the last three days on this subject. Have not found anything to back up one way or the other.  Its about split 50/50 between installing the sensor in the cooler line or the pan.  Lots of peeps giving their opinion, but no proof to sway either way.  If one way is truely better than the other, I want to do it that way.  Just not convinced yet. 

[Rickf1985]

My recommendations are based on fact and my 40 years of racing and building experience. I have the documentation to back it up but it is in print from GM, Allison, TCI, Trans-Go and others and is in technical bulletin format and at the moment I have no idea where it is in many volumes of manuals. Then I would have to scan it an post it. At this time I am too busy at work and trying to get ready for a trip at home. You will have to take my word for it or not. Your choice.
I have nothing more to add.

[circleD]

My old school way of thinking is if you read Ricks and CNCs post they're both correct. Where ever you put your sensor due to labor or money issues just remember where the hottest fluid goes and the coolest. And if you put your sensor in the pan just remember that it might be a few degrees hotter in the system.
Also just a FYI I put a tranny sensor in an old truck years ago where I "thought" was a good spot and the sensor hit the inside and I couldn't put it on. Got another junk pan then recalculated my new hole  . I used the old pan to practice welding and shooting  . So check before drilling and check the ground clearance.