Guys,

My Temp/Oil guage has stopped working on my '77 280z. It use to be just the Oil...now the Temp is past the 250 mark...and driving to the show on Saturday during that hot weather had me wondering. Is it simply changing the sensors or is a full replacement needed. Does any other first gen had a similar experience ??

Thanks,
alzee

Al ~
Funny you should ask.

One of the very first and most-frequent complaints on the early 240s was that darned inaccurate Oil Pressure gauge and sender unit combination, which ALWAYS seemed to indicate low oil pressure. Our Member Dan Linquist out in Washington state could probably tell you lots of stories regarding customer complaints, and since he was a line mechanic for the Z cars when they first came out, he could tell you tricks to fix it.

MOST of the time the pressure was OK; I hesitate to say that to anyone in case their pressure isn't OK (which would also be indicated by a rise in engine temp, which you said you got). Many times it was the cheap oil pressure sensor on the passenger side of the engine block which was to blame ~ a quick and inexpensive fix if that's the problem. Just screw in a new one and check the reading. If it's improved, you're golden. If not you can go to the more-expensive (but still not prohibitive) act of replacing the gauge, too.

Your very safest bet is to test the pressure with a screw-in tester, to ensure you know just what pressure you have at various RPM and temps. I'll dig out my service manual and have step-by-step ready in case nobody else comes up with a better answer before I get my hands on it.

What shape is your cooling system in? If the engine really did reach that temp or close to it, your oil would thin out and you would experience an actual drop in pressure, even if the gauge/sending units were good. Older lower radiator hoses can collapse from vacuum/cavitation at speed (hiway driving, for example) and limit the amount of cold water returning to the radiator. As soon as you stop to look things over the hose pops back to its original form, and you can't tell by looking at it that anything is wrong. One of the 'backwoods' checks for that was to crest a hill, depress the clutch and coast downhill at speed with engine at idle. If the temp drops dramatically then rises again when you get back on the gas, the hose is suspect. If you're Superman you could squeeze the lower hose to see if it's soft enough to collapse, **BUT YOU'D BURN ALL YOUR FINGERPRINTZ OFF** They started putting coil springs inside them to prevent that, but I don't know what year. If your radiator has damaged veins or fins or is leaking coolant or if your fan belt is slipping, your engine would get uncomfortably hot too.

Driving my old Z in Hawaii, the Carolinas and cross country, I was often forced to turn on the heater (in summer) and remove the inspection lids from the hood to keep the temp down. Finally I broke in and bought a 4-core copper radiator and my problems went away (after I had replaced the sending unit about 3-4 times).

Check everything over and I'll go look for my manual after dinner. Squeeze the lower hose (cold please), check fluid levels and try the fanbelt.

Frank

Al ~ Didn't mean to abandon you, sorry. Couldn't find the manual but if memory serves, the mechanical oil pressure simply screws into the port normally occupied by the pressure sensor on the passenger side of the block and the most important items you need are a pen & paper. Record the pressure at cold idle, warm idle and warm at-speed. Compare them to the mnfr's specs and decide if the engine is OK or not. Regret the delay, my life is a bit crazy this month and I have trouble finding time to do my own stuff.

Those standard gauges r bloody hopeless. The gauges themselves r usually pretty accurate. All depends on your sender units. I've had Z's showing low oil preassure which was just the oil sender unit on the side of the block.

Oil Preassure gauge.
The best thing you can do to be sure is replace the electric oil pressure unit with a solid line sender unit..INstead of an electric wire going to the unit and gauge it has a thin metal line. These r full of mercury so your gauge operate's instantly according to the revs. You will need a new after market gauge to run this. These gauges r zero delay. so when you rev your engine the gauge will go up instantly. This way you'll know exactly what your oil preassure is doing in the comfort of the front seat.

My opinion is replace the oil/temp gauge with individual gauges. Lose the clock. Its not original but it works.
Its too risky to trust the old factory stuff to be accurate. some cars they last forever on, other cars they just die in the arse.???

Z's can be fussy when it comes to cooling. 1 little leak can stuff the whole system up. I hate trying to figure out heating probs, cos you can change everything and still run hot... Always try to run a 3 core radiator at least.
All Automatic cars should have these. excellent cooling compared to the 2 core.
Get yourself a hand held temp gauge tester and check the accuracy of the gauge.

Those darn oil sending units have always been a problem, but not to worry, I've never had a Z just loose oil pressure. Unless your losing oil, it comes in handy and the first sign of low oil, old thinned out oil, or the rare case of just loosing some oil pressure, is that the valve train will get noisy. Water temp is important, I would concentrate on fixing that first. I think on the older Z's you can just gound the sending unit wire to the block and this should show the gauge is ok. Most likely its the sending unit. One wire units rely on the body ground, so if you take it out and clean it, threads and all, it might work again, and don't use any silicon or teflon tape on it.