Oil Temp Gauge

[1981]

My Oil Temp Gauge does not work. How do I get this to work? Are there common problems associated with this gauge I should start looking at first?


Thanks,
1981

[ksems]

it may be your oil pressure sender located at the back ( drivers side ) of the intake manifold....pretty easy to replace and I think it is only about $20-$25....not too bad.

good luck

Kevin

[LannyL81]

I can tell you that the oil temp gauge has a sender in the block and the gauge itself; that is all there is to it. I would think that if you grounded the lead going to the sender (with the key in the ON position) the gauge needle will either peg left or to the right. Now if you used something like a 100 ohm resistor, on the sender lead, the gauge should show somewhere in between.

I do not know the resistance range of the sender; it may be stated in the 81 Service Maual, would have to look. If you get no response out of the gauge at all, then either the wire is broke between the sender and the gauge or the gauge iteself is toast.

I know you can get new senders from GM still; I can get you the part number if needed.

Good luck,
LannyL81

[geekinavette]

The oil pressure sending unit's resistance goes up as pressure goes up, therefore if you ground the gauge lead at the sending unit the reading should go to zero.

Bill

[1981]

Thanks, I will be trying all of this out tomorrow. I really hate taking the middle console apart though, it is a pain to put back together. But such is the joy of driving this road magnet.

Thanks again,
1981

[1981]

Update to this problem, I finally got my assembly manual and started picking at this problem. Come to find out my "Oil Temp Gauge" does not work because the oil temp sending unit is connected to the wrong gauge, the "Engine Temp Guage"! So the problem is not whether or not my "Oil Temp Gauge" works, which when I hook it up correctly I hope it works. It looks like my "Engine Temp sending unit" is not wired up or does not work.

I need to take my dash apart, Arrrgh, (that is going to be a long day) and straighten this mess out. And to think I have been watching my Engine Temp Gauge as if it were my oil temp gauge, knowing it was the oil temp I was monitoring and not realizing it was on the wrong gauge. Geesh, even I didn't understand that sentence.

I have looked through the assembly manual but can not find where the engine temp sensor is located. Any clues as to where to start looking would help out a lot.


geekinavette wrote:
The oil pressure sending unit's resistance goes up as pressure goes up, therefore if you ground the gauge lead at the sending unit the reading should go to zero.

Bill


I did this and the needle pegged to the left, not to zero.

1981

[geekinavette]

Isn't zero to the left on the gauge :confused Or are you saying that the needle went PAST zero to the left? If that's the case then that's probably normal.

I had a similar problem when I bought my '84...they had the O2 sensor and temp gauge sending unit wires reversed. OOPS!

I'm not exactly sure on an '81, but the temp gauge sender is usually in one of the cylinder heads (probably driver's side). Hopefully someone with an '81 will verify if this is right or not.

Bill

[1981]

Ahh, your right, in my hast I said it went to the left when I meant right.

As a correction, the needle pegged out to the right past 80.

Thanks for catching that.

1981

[geekinavette]

Hmmmm......that seems bass-ackwards ('course maybe it's me that's bass-ackwards!). Does the needle go to zero when you remove it from ground or the sending unit (just let it "hang")?

Bill

[1981]

Just disconnected the connector from the "Oil-Pressure Sending Unit" and the needle immediately pegged to the right past 80 when I turned the aux power on, and stayed pegged as I started the engine.

>>but the temp gauge sender is usually in one of the cylinder heads (probably driver's side).

Would this mean it will be much harder than messing with one of these other sending units? Man, I wanted to troubleshoot this tonight and get it over with. Can anyone confirm the location of the "Temp Gauge Sender"? And what it would take to get to it and troubleshoot it.

Thanks,
1981

[geekinavette]

Wait a minute, I'm getting confused here. When you remove the oil pressure sending unit connector the gauge should peg, that's what I would expect. Now when you ground the sending unit wire that goes to the gauge, the needle should go to zero. If the gauge is pegged whether the wire is grounded or disconnected then either the gauge is bad, the circuit is open between the sending unit and gauge, or you have the wrong wire.

The temp sending unit should be easy to get to. look on the side of the driver's side cylinder head between the exhaust ports for cylinders #1 and #3. It will have a single-wire connector, usually a spade-type (again I'm not sure exactly for an '81, but this is typical). If you don't see it on the driver's side head then check the passenger's side between #6 and #8.

Bill

[1981]

It sounds like I have totally confused not only myself but you also. I am going to start over with the troubleshooting:

The oil temp sending unit is working through the Engine Temp gauge.
I am sure your earlier statements on how to troubleshoot the oil pressure sending unit are correct, I will redo this part again tonight since I really have confused it badly.
The oil pressure gauge works fine. Reads around 40 and works upto 80 during driving since I have a rebuilt engine with a high pressure oil pump.
The Engine Temp sending unit does not work. The gauge like above works since the oil temp sending unit is wired to it. But I have no Engine Temp where the oil temp is. This little fact has litterally confused me badly while troubleshooting this. Sorry for really mucking up your statement.

So where I am at now is I need to start figuring out if the Engine Temp sending unit works. Where would I locate the Engine Temp Sending Unit?

Thanks for fixing my confusion,
1981

[geekinavette]

Ahhhh, now I get it.

So just look for the temp gauge sending unit as described above, on the side of one of the cylinder heads between exhaust ports.

Bill

[Yoda]

1981 I scanned the page from the 1981 Assembly manual that shows the Oil and Water Temp sending units.. hope it comes through ok for you ;)

BudD
:bu :w

[1981]

Thanks a lot for the scan,

Just got back from my first corvette show! A local corvette club show for Lafayette, LA. There must have been about 100 cars in the parking lot. Mine was one of them :gap . Was a lot of fun and I met several people from the area. I guy even showed me exactly where the temp sending unit was! I really can not express how great it was to be around so many corvette related people. I am sure you know exactly what I am talking about. It was great. I will be troubleshooting more in the morning and will let you know what I find out.

Where can I get a replacement if this is the problem?

1981

[Yoda]

1981,
Sounds like you had a great day ;) There are many more to come :D

If you need a new unit, your local Chevrolet Dealer Parts probably have one, or any major parts house e.g. NAPA, Autozone etc..

Happy motoring :w

BudD
:bu :w

[1981]

OK here is the news,
Got under the car today to look for the oil-temp sending unit. There is not one. Although I did find the connector for it, and put a 100 ohm resistor to ground on it. It gave me a reading of about half in temp on the gauge! Great, so that means I am half way there, the gauge works so the sending unit must be the problem. But, there is no sending unit between the last two exhaust ports on the drivers side, but there is an Engine-Temp sending unit between the front exhaust ports on the driver's side. This sending unit works great. Can this sending unit be used either or for Engine Temp and Oil Temp? or Does the location of it really matter?


How can I not have an Oil-Temp Sending Unit? Does this mean my engine is not a L81? The assembly manual drawings do not even note the location of the engine temp sending unit. Which as I found is located on the driver's side front of engine. Boy, this worries me now.

Can someone comment on what they think is going on here with my engine?
Any ideas on where to go next?


1981

[geekinavette]

This is my fault...I misunderstood and thought you were looking for the cooling temp sending unit.

Look around where the oil filter attaches to the block, the oil temp sender could be in that area (it is on an '84). If the connector is in that area and you find a plug in the block near the oil filter, then I guess just buy a sending unit and install it there.

My apologies for the misunderstanding.

Bill

[1981]

I looked near the oil filter where I found the connector and can not find the sending unit anywhere. I have also looked for a plug, but can not find that either. I took the spark plug heat shield off to get a better look around this area, but nothing. I'll keep looking.

1981

[1981]

There is a small plug right above the oil filter. About 1 inch above where the filter screws into the block. The plug is in a place for the connector to reach perfectly. It does look smaller than the engine temp sending unit hole though.

what do you think? My engine was rebuilt and the plug has never been taken out since it was painted blue. If this is the plug do I have to drain the oil before I can take this plug out?

1981

[geekinavette]

Yep, that's it!

I dunno how much oil will come out when you take the plug out, I doubt that you'd need to drain the pan first. Just have the sending unit ready to stick in there as soon as you get the plug out.

Bill

[1981]

Thats great! I'm off to the store. The fan sending unit on the opposite side of the engine needs a new connector so I will be changing this also. It is brittle, all I did was look at it and it broke.

Thanks, I'll let you know how it all turns out.

1981

[Yoda]

1981:
How can I not have an Oil-Temp Sending Unit? Does this mean my engine is not a L81?

In 1981 the oil temp. gage was optional, and standard with the Electronic Radio. The radio had a clock so the analog quartz clock was replaced with the Oil Temp Gage ;)

[DDLS1]

Only a small of oil will come out if you remove the plug. About the same amount as when you remove the oil filter.

[1981]

Any ideas on how to loosen this plug? It uses a (forgot the size allen wrench). It was installed before the engine was painted after rebuild. I can not get it to budge. Righty Tighty Lefty Loosey.

Man, this oil temp has really worked me over good, and still hitting me with problems!

1981

[geekinavette]

I would probably get me a hex adapter and a long-handle ratchet or handle. Those pipe threads can be pretty tough to break loose sometimes. Just make SURE you have a good bite on it before you put a lot of "oomph" behind it....don't wanna strip that hex hole out!

Good luck!

Bill

[1981]

After all my effort I have found I do not have the proper tools to get this Hex plug out. I have the Oil-Temp Sender and will pass by the local mech shop and have them remove the plug and install the sender. Thats pretty pitiful, but I figure they can do it in about 5 minutes with the proper breaker bar.

I can not tell you what it has meant to me to have all of you support me through this Oil-Temp problem. After the shop installs it, my Vette will be that much user friendly again. Thanks,
I will update you after I get it installed.

1981

[geekinavette]

Well it's better to be safe than sorry, that's for sure! Let us know how it goes.

Bill

[1981]

Monday I had a local mechanic shop break the plug loose and install the Oil-Temp Sending Unit. But the Unit was too big for the hole. Come to find out it looks more like the Engine-Temp Sending Unit than the Oil-Temp. Well, this took me on a journey to find the correct part. AutoZone, PepBoys, O'Riellys, Performance Shops (won't even bother with these shops again, looks like they are only selling to the "Fast and Furious" crowd. Told me they could not even cross reference the part for me, let alone order it)

So I ended up calling my local Chevrolet dealer, who has told me when I called last week for a compression check, "we do not work on older corvettes." Well, they don't even work on their newer ones either, everyone I talked to at the Corvette show this weekend told me they bought their car there, but would never take it there for repairs. Is this normal, or is this dealership pretty poor when it comes to mech work? I have a friend that told me he does not take his 2002 truck there either. Well to make a long story long, I showed up at their parts department since the guy on the phone could not understand what I was talking about. We both looked through their parts computer and found this part:

Oil temp sending unit
25036292 w/ stereo, C.B.

I know the Oil-Temp Gauge was an option when the radio supplied the time (the clock was replaced with the Oil Guage).

But every parts store I visited could not bring this part up. "Oil-Temp gauge! What do you need to know the oil-temp for?" Well, because my car has one and I need to install the correct sending unit. I have the money, you sell me the part.

So here is my new problem, the part comes in Wednesday at the dealership, (I am very wary that this will be the correct part) has anyone ever replaced or has anyone ever seen this actual part? My engine was rebuilt and a plug put into its place. I have to rationalize there was a reason for this. Does this sending unit inhibit the flow of oil near the oil filter?

This part looks like it is hard to come by, should I buy the only two they can locate? So that when this one breaks I can replace it in years to come?

As reference, the Engine-Temp Sending Unit has a 1" size thread, the Oil-Temp Sending Unit looks like it is 1/2".

Thanks for the knowledge,
1981

[DDLS1]

1981,

I'm pretty confident that this is the one, but I'll take a look at mine later on and post for you. Take a look at this one http://www.ecklers.com/product.asp?pf%5Fid=20117&dept%5Fid=1309

[DDLS1]

1981

I looked at my oil temp sender awhile ago and it is a fair amount smaller than the water temp sender in the head. So it sounds like you have the right one coming.

[1981]

That looks great, and may be the one also. Every oil-temp sensor I have been able to hold in my hands at the parts stores have threads going all the way from the temperature probe to the nut. Their thread sizes are about 1". But this one at Eckler's sits out about an inch which looks as if it would fit perfectly right over the oil filter. I wish I knew what size the threads were on the Eckler's one. From what I have learned so far, the plug from my oil-temp sensor hole has threads which are about 1/2". So the oil-temp sensor needs to have 1/2" threads.

The price for the oil-temp sensor from Chevrolet is $31.00 +tax I am sure. It should be in tommorrow, which would be nice. Since the plug has been broken free already I can put this in myself. Send me a pic if you can get it, if not, when I install the one I get I will then take it out and take a pic of it. This will give anyone else who has trouble finding one a reference to look at. And hopefully a correct part number through Chevrolet.

You all have been lots of help and a lot of fun with this problem,
Thanks,
1981

[1981]

Received the new Oil-Temp Sensor from my local Chevrolet parts department and it is the correct part. I took some pictures of it out of the box and installed. I will be posting them as soon as I get done with some of my "honey do's". It works great, the gauge finally works! I will also write up a how to replace this part for if anyone has this or another Oil-Temp Sensor problem in the future. Pretty basic all the way around, but I would have loved to know a couple of things before hand.

Thanks to everyone who helped out.

1981

[geekinavette]

:beer

Bill

[Dave L.]

1981- That is a sharp looking car you have there!! After reading this post I am glad you got your guage problem solved.

Dave

[1981]

Thanks, I am currently in the process of taking good under carage pictures since the car was off- frame restored and powder coated, everything under the body is brand new. Exhaust, front/rear suspension, SS brakes with new lines, steering, a lot of new engine bay components, bearings/bushings/seals/struts/arms/everything. Engine rebuilt, trans rebuilt. I do drive this car as much as I can, ("Honey we need some bread" and I am out the door). I enjoy this car too much. So I try to keep the under carage components clean. I believe the exhaust and rear suspension are the most prominent feature of this style corvette from the rear. The paint and the interior do need work, but all in all the interior only needs new carpet which I want simply because I hate old carpet (20 years of filth and grime). The paint will come along in about 2-3 years. And I need glass T-tops! The fiber T-tops are nice, but glass is much more like this style car. My budget for projects has dwindled down to hardly nothing, but my next project will be to incorporate the bigger speedo.

By the way, I really know nothing about the type of tires on my car right now, except my type tire is no longer made. I have Goodyear Eagle GT +4 tires. Each tire is practically brand new. I would hate to be burning up 4 really good tires I can not buy anywhere else. So I stopped by Goodyear the other day and found some GT II tires. Are these the only high performance type tires out there right now for the C3?


I am still working on documenting the Oil-Temp sensor.

1981

[GerryLP]

I noticed that my Hi Performance short block has the threaded port for the oil temp sending unit, but it is "blocked" by something. It looks like part of the block casting. I cannot notice any slots or wrench flats in it. However, the hole is threaded.

I compared the hole with my stock L81 short block, and the hole is in the same location as my stock block. The hole in the stock block access the oil filter connection. I guess it senses the oil temperature after filtering??? Does anyone know??? :confused

[geekinavette]

No idea Gerry, sorry.

Bill

[1981]

I will be posting pictures of the installation of my oil-temp sensor soon. It installed into a small 1/2" hole right above the oil filter. My engine was rebuilt approx. 2 years ago and the hole was plugged rather than re-installing the oil-temp sensor. Go figure, because all I did was re-install one and everything works. I did have to replace the brittle connector, but that was not a problem either.

1981

[DDLS1]

GerryLp,

Given the sensor location on the filter housing I would say the temp is read pre-filter. Even so, pre-filter or after filter the temperature should be very close to the same.

[GerryLP]

1981,

Did you post the sensor replacement procedure? If not, then don't worry about it. I know that it is pretty simple, but I am still wondering if I need to drill-out the internal passage for the oil sensor or does it need just to make contact with the block casting metal. :confused ...then Let me explain...:

I have a Z28 2-bolt main casting block number (which I have checked, but I can't recall the number at this time). I plan to ask my engine builder if it was modified as a 4-bolt mains, but it probably won't matter since my research has shown me that 500 Hp (plus operation below 6,000 rpm) and under is fine for a 2-bolt main. Anyway, the port for the oil sensor is open (the threaded part), but there seems to be a casting plug of some kind inside the hole past the threads. Does the sensor just touches the casting part of the block or is it supposed to be in direct contact with the oil itself. (I should probably be on the other side of this sign ;stupid, but I never removed it from the factory L81 block, and since the new engine build, I can't tell if my engine builder removed something from the original block :confused....:L I guess I cannot explain this issue very well....:help

[yellow81]

if you don't have the sensor, will the wire be there anyways? I haven't checked yet, but my gauge is not working either. So I don't know yet if I have a sensor or if it is plugged. I believe I have a factory radio with digital read-out, but my glove box has the 8 track slots. Am I just babbling?

[DDLS1]

yellow81,

Look down on the left side of your engine block at the spot where your oil filter screws on. The oil temp sending unit(if you have one) is in the casting just above the oil filter itself. Now on your digital radio......is there a chrome area that says corvette? If there is, push on it to see if it is the 8 track door. The Chevrolet 8 track players had a door that the tape went into that was so oblivious that many people did not realize they had an 8 track player. If you have an oil temp gauge and a factory digital radio, then you have or should have a wire.

[yellow81]

DDL-81, I did find the sensor and the wire hooked up to it. My sensor, I'm thinking must be bad. My radio is a cassette player, nothing saying Corvette. Could it not be a factory install? I have the same radio in my '88 Chevy dump truck. Thank you.