Topic: oil pressure and temp gauge

[Daz78]

i have just bought a new oil pressure & temp gauge for my 78 trans am, i have not removed the dash bezel yet but looking in the haynes manual it looks like the whole cluster is all in one when ya remove it. was there two different types or can the temp gauge be replaced on the cluster.  regards

[Anderson0741]

No you can just disconnect them.  I tried to find a picture of one of my cars but couldn't, its just 4 screws around the outside of the gages, then just the temp and oil gage slide out.

[Daz78]

Hi, thanks for that. thats put my mind at ease.

[Anderson0741]

Yep, its not bad at all, there are a couple screws under the dash bezel that you need to unscrew from the bottom too.

[Anderson0741]

Dangit, my bad that's how you remove voltage, and gas gages. I have no idea what I was thinking and I'm done giving advise haha, sorry for mis leading you.

[Daz78]

Hi, Thanks for that hammer,  it looks ok to do, i have removed instrument clusters from cars in the past and on some of them everything is together and nothing can be replaced seperately, ya gotta buy a complete new cluster.  thats what i was worried about,  i can now see that on the trans am the speedo, rev counter or temp gauges can be removed and replaced seperately. and i have just bought a 100mph speedo from the us so i will replace that too. my 78 trans am has been in the UK since it was new and for some unknown reason the speedo is in kilometers (factory Fitted). i will let you know how i get on.   regards daz

[Daz78]

Hi hammer, here is a picture of the Kilometer speedo. sorry its a poor picture,  Note that the KmH is the white on the outside and MPH is the blue on the inside and only goes upto 80MPH. the speedo works perfect so i may stick it on ebay . it may be worth something , i dont know.  Also you can see my water temp gauge, i turned on the ignition one day the needle shot right over and now its stuck pointing down and also the oil pressure needle is stuck on the red even when the car is not running . LOL.  regard daz

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[OrigOwner77]

Daz,

The printed circuit board tape (membrane as Hammer calls it) also tends to break very easily. What I mean is the metal contact strips you see running along it can break and connections become lost or erratic. Do be sure to inspect the circuit board closely (trace the circuits and verify everything looks good) while you have it apart and order a new one if you need to. No sense doing the job twice.

Your gauge issue is interesting.....usually when a contact breaks with the oil psi and temp gauges, the oil gauge pegs at max (80+ psi) and the water temp gauge sits at a zero reading (100 degrees). Yours seems to have done the opposite. 

Do let us know if the gauge fixes it. Good luck! 

[Daz78]

Hi, yes i will look at the printed circuit board, my friend can check for breaks and repair them as he is an electronics wizard.
hopefully it should sort everything out.

i was also wondering if the temp sender on the engine had gone, but i am not too sure where it is.

i seen something on the left side cylinder head just near the first plug lead.  it had one wire going to it, i removed the wire but nothing happened.

i am not too sure if that is the temp sender,  if not then where is it.

daz78

[OrigOwner77]

Hi, yes i will look at the printed circuit board, my friend can check for breaks and repair them as he is an electronics wizard.
hopefully it should sort everything out.

i was also wondering if the temp sender on the engine had gone, but i am not too sure where it is.

i seen something on the left side cylinder head just near the first plug lead.  it had one wire going to it, i removed the wire but nothing happened.

i am not too sure if that is the temp sender,  if not then where is it.

daz78

Yep...sounds like the temp sender. Green(?) wire if I remember. Oil psi wire is either brown or blue, depending on years (I'm pretty sure).

When you disconnect the temp sender wire, the temp gauge will sit at the lowest reading (100 degrees). If your gauge hasn't moved from that point, then it will appear to have no effect when removing the wire. Ground the wire, however, and it should peg the gauge up near 260 or whatever the highest point is. Remove it and it'll drop again.

Oil press gauge test is the same way; just reverse the results. Unplugged = max reading, grounded = 0 reading.

EDIT: And not to point out the obvious, but make sure the key is ON when testing. Made that mistake once.....

[bluebyu64gp]

Speaking of gauges, anybody convert to Auto Meter or such?  I want to go with the Covan (Now Classic Dash) bezel panel with yet to be undetermined gauges from Auto Meter...I apologize to the purists, but the stock gauges and their electrical gremlins drives me nuts.

[Daz78]

Thanks hammer and the other members,  Here in the UK we have another postal strike, so it looks like monday or tuesday now before i get my gauges. i have looked into it and it dont really look like a bad job, i have done worst, i changed the heater core last year. nothing can be more of a horrid job than that.

I have the car for sale at the moment and it is also on this site for sale, under 1978 black trans am

so i hope to fit the gauges before it sells, as i want the car perfect for the buyer.

i cant sell it with a broken temp gauge.

i will let you know how i get on

Daz

[ta78w72]

Purchase a variable resistor 500 ohms.  Then you can disconnect the lead to the sender (oil, temp, or fuel) and connect it to one of the end terminals of the resistor.  Ground the middle terminal (there are three terminals and it doesn't matter which end terminal you use....but you must connect the middle terminal).  With the key on, turn the resistor knob and the gauge needle should move.  It if doesn't you've either have no voltage to the gauge, a broken wire, or a bad gauge.  If the gauge does react, the sender is bad.

On the fuel gauge, there's a connector in the trunk by the lock with a pink wire and a brown wire.  That's where you disconnect and connect the resistor.

Variable resistors cost about $7 at your local electronic store.

I just did this on a fuel gauge with John007.  We determined his fuel gauge was bad.  We pulled it and I bench tested it and verified it was bad.  I had a spare he used until he could buy a replacement.  Took all of 25 minutes to get to the bottom of the problem.  Better than assuming that the sender was bad as we thought before I tested the circuit with the resistor.

[Daz78]

Thanks for that info.  if i do need a new water temp sender or an oil pressure sender. how much are they to buy.

Where is the water temp sender on the engine ?

where is the oil pressure sender on the engine ?

i would look in the haynes manual but it would proberly tell me to take it to a pontiac dealership.

thanks

daz

[ta78w72]

Pontiac 400...temp sender in the head between cylinder 1 and 3.  Oil pressure sender is near the oil filter.
Olds 403....temp sender on the intake manifold front.  Oil pressure sender...line runs over the water pump to the sender which is on the drivers side on the pump.  It floats.