ray green

iTrader: (14)

OK, this was too weird not to share with you guys. And yes Doc, I did a search.

On my way home tonight I discovered my headlights are making my car overheat, which has been happening about once a month for the last year. It was especially bad last November, when I was commuting in the cold predawn mornings, you wouldn't think a car would get hot then. And it has cropped once in awhile since, more or less randomly I thought, including tonight.

So I was totally stuck in Atlanta rush hour traffic, which is why I go home early most days. Of course I put the lights on because everyone else is, and of course for the first time this month the temp gauge goes up.

****, another drive home with a hot engine (55 miles in my case). But then, I've been doing this every once and awhile for the last year (40,000 miles), so I knew the temp gauge would run hot until I got home, then be fine in the morning.

But anyway, I'm stuck in traffic without much to do and I start looking around at the gauges, which are lit up because the head lights are on, even though it isn't dark (one of the really nice things about the 84-85 GSLs, those lights on the dash and the console).

So I notice the amp gauge is reading low, which I wouldn't unless I was bored, and being into gauges at the moment, I turned the headlights off.

Well the amp gauge goes back to normal, that's nice. But then I notice the temp gauge returning from it's hangout in the danger zone, back down where it belongs.

Whoaa, not a bad fix.

Sure enough, every time I put on the lights, the temp gauge goes up and when I turn them off the temp gauge goes down. I just happened to have the camera in the car so I snapped these pictures with the lights on and off over a few miles (recorded on the odometer and dash clock). Here's a few cycles:

Lights on:



Lights off:



Lights on:



Lights off:




So, my question, fellow rotor heads, is what the **** is going on?

Ray

Rogue_Wulff

Temp gauge must be feeling the heat of dash lights....
Seriously, I have this same type of thing occur in my '83, only not quite as drastic. The gauge reads just a tad warmer with the lights on, and drops almost instantly when I turn off the lights.
I figure it has something to do with the extra load on the electrical system causing erratic gauge readings.

mazdaverx713b

iTrader: (91)

Ray, i had this same problem with an 81 GSL that i had and could not figure out the problem. what was happening was that when the lights were on the temp gauge would peg. with the lights switched off, the temp gauge read normal. the engine never overheated with the lights on or off as the gauge had indicated. must have been something with the wiring. never figured it out and sold the car some years ago. i'd be interested if you find anything out!

FirebirdSlayer666

iTrader: (3)

Not enough ground on the negative battery cable. Had the same problem when I replaced my cables and didn't run a second ground. Hook up some 8 guage wire from the end to the strut tower and see how that works

Rogue_Wulff

That sounds very plausable. My ground cable (original) is a little nasty looking where it bolts to the strut tower, on the way to the engine. Been meaning to clean it up, but it hasn't caused me any grief.......yet.

Rx-7Doctor

iTrader: (13)

Grounds are the single most important part of the wiring system. More grounds added are not really needed if the original ground wires are in good condition and there is no corrosion where the grounds attach.

Man_in_black49464

iTrader: (1)

It is a ground issue RAY.
The wires that have the lights run to them are in the same bundle that the temp sensor is on, they ground at the same point under the hood, make sure all your wires that mount to the body are solid it wouldnt hurt to take them off and use a little sand paper on them to make them connect better!

trochoid

iTrader: (6)

Since the gauges measure by resistance, not having good grounds would be the logical answer. Particularly if the reading change is instantaneous.

mazdaverx713b

iTrader: (91)

would you think that a good place to start would be the ground on the left strut tower, then moving on to the ground at the bellhousing?

ray green

iTrader: (14)

I like the weak ground idea, the "overheating" is related to load. The tansition is slow, taking about 30 seconds to fully readjust, and I get about half as much deflection if I turn on just the running lights without the headlights. Even the radio has a small effect and this morning I discovered I can dial up four different temperatures with my heater fan.

I'll go over the battery ground (which has never been that good) this weekend and check for other bad connections, maybe at the sender unit and report back.

Ray

bliffle

Let us know how it turns out. Sometimes a guy solves his problem and doesn't report back here so we all wonder what the solution was.

ajhehr

may also swap out your coolant or at least check it for some electrolysis.
Ive had it through off the resistance in the temp sensors before.

ray green

iTrader: (14)

What kills me is that over the last year I have scrutinzed every aspect of the cooling system trying to figure out why my temp gauge would wander around, including fresh coolant, rad caps, thermostats, efan's, once every three or four weeks.

In retrospect I should have been smart enough to look for electrical problems, but it happens so infrequently (I don't do a lot of night driving) and at the weirdest times (like early predawn winter mornings - lights and heater fan - or when it's raining - windshield wipers or probably, in retrospect, when I just had too many accessories on at once. Maybe even the ambient humidity was affecting the ground connection, making it even more unpredictable.

Because the slow temp change an correlation with highway speeds, I just assumed the gauge was right and it was somekind of weird cooling issue. But it's all adding up now, I'm betting dimes to dollars on that cheap-assed Autozone aftermarket battery clamp to the ground wire, or maybe one of the other grounds as mentioned above.

Hopefully I'll find it this weekend, I'll let you know.

Thanks all for the helpful feedback.

Ray

Rogue_Wulff

Yes. Start with the connection at the strut. Lights, wipers, heater/ac blower, radio, and everything else that is grounded to the body, relies on that connection.
The starter and engine systems rely on the bellhousing connection.

Funny thing is, I know all this stuff, and never put the funky acting gauges and weak ground issue together. Like I said, it hadn't caused me any grief, yet.
I didn't even make the connection, after having to solve the issue on another car. My buddies 79 would shut off the fuel pump, when the lights were turned on........

trochoid

iTrader: (6)

There is an engine ground wire from the block to the firewall that I have found missing on many 7s. The firewall ground wire brings the rest of the electrical system grounds back to the engine. Also keep in mind the alt grounds through it's body>engine>neg battery cable.

mazdaverx713b

iTrader: (91)

where is the location of the ground on the firewall?

ray green

iTrader: (14)

OK, I think I've finally got it figured out. And you folks who were betting on a ground issue (me included) were on the right track, but not exactly.

First I pulled the temp sensor from one of my other cars, cleaned it up and replaced the one in the car giving me trouble. The one I replaced was a little beat up, it had obviously been removed a time or two, but this replacement didn't have any effect on the lights on/lights off situation with the temp gauge.

So then I cleaned up the battery cable tie downs, hot lead first because it was looking a little funky (though I've seen much worse).

Anyway, that fixed the problem, so I guess it wasn't a ground afterall:

Headlights on:



Headlights off:



I also noticed the voltmeter was reading a little higher, up around 14 volts like it should, instead of just above 12.

Here's a picture of the crappy battery cable tie downs that came with the car, now that I know they are causing problems I'll replace them both:



So it appears the long saga of the wondering temp gauge is over. I hope.

Thanks to all who got me looking for something electrical instead of the cooling problem I thought I had.

Ray

Kentetsu

I was going to ask if your alternator belt was tight. When you turn on the lights, you put more load on the alt. If the belt is loose, then you might start slipping on the water pump (do you have the rat's nest removed?)....

ray green

iTrader: (14)

I've got the rat's nest in there and everything is working except the air pump doesn't go to the cats, which aren't there. In fact, I had taken the air pump out at one point and put in a block off plate, but this caused the car to idle rough and I was worried about alternator slippage with just one belt. So I put the pump back on, the car idles smoothly again, but the temp guage would still creep into the hot zone from time to time.

But you've got a good point Ken, that would fit the symptoms. In fact, the temp guage was behaving perfectly on the 55 mile commute in this morning, which I did in the dark with the headlights, radio and fan on. I was sure the problem was solved. That was until I reached my exit ramp and noticed it was drifting up again, not as bad as before but still real annoying. It could be those battery tie downs need to be replaced (cleaning wasn't enough) so I'll see if Autozone has anything better this evening.

Still, maybe I'm chasing another false alarm, so I'm liking your idea.

Maybe it's slipping a little only when the car is hot, slowing the water pump (this is one reason I'm working on installing a second temp guage, to tell whether the temp rise is real or just in the guage). But the belt is practically new, in great shape and tight. There's been no evidence of slipping (shiny belt, belt noises) and of course I've been keeping an eye on it all along. Still, maybe it's just happening when the car is hot (like when I got off the exit ramp this morning and unlike in the test in the photos above) just enough to cause some heat up without actually overheating. I'll check out the belt again tonight and I have some other good belts, so I'll switch to a different one.

Kind of a nuisance, but at least the car is running great. This one kind of reminds me of my MG.

Thanks for the suggestion!

Ray

ray green

iTrader: (14)

Just to put this one to bed, it looks like it was the the battery terminals. I found this rather pricey gold plated positive terminal ($15 autozone) with two connectors (actually four), which you really need with our cable set up, and it works works much better. They sell a gold terminal for the ground to, but they were out of stock so I got an inexpensive brass one ($2.99) for now:



It's only been one day, but the temp gauge behaved itself all the way in and back, in stop and go traffic and at prolonged highway speeds, lights on and off, without drifting.

Yes!

Ray

trochoid

iTrader: (6)

Very fancy there Ray, it's good to see that you treat your car to the best quality parts. As a side not, I've found many pos battery cables that once they start to corrode at the battery terminal ends, the corrossion has grown underneath the plastic sheathing, hidden from view. Simply replacing the connector will not solve the problem if this is the case. Then it's best to cut the cable back to where the corrossion is gone.

dj55b

iTrader: (2)

Just for further reference ... i had a similar problem last year and it was tracked down to a bad alternator. It drove me crazy, because it would show that my temp is all the way up and I would stop every 5 minutes afraid that something would go out on me. So a 20 minute drive took almost an hour

ray green

iTrader: (14)

Well sure enough yesterday the temp gauge was fine but this morning, during the predawn drive into Atlanta, it's back to it's old ways. Same symptoms, once I'm out on the highway and up to speed, the temp gauge drifts up to just below the first warning market and just hangs out there, all the way into Atlanta (a one hour drive at 70-80 mph).

While the problem always seems to be related to the headlights (for example, when I turned them off briefly on the way in this morning, down comes the gauge) it seems to also be related to those early morning drives in to work. Yesterday I did the same trip but in mid morning, same speeds and everything but with even more stop and go traffic around Atlanta, and the guage didn't budge, so I thought I had it fixed. But the combination of headlights on and predawn mornings does it every time. Very weird.

So I guess it's not the terminals afterall. And yes dj, as it turns out I did swap out the alternator a few weeks ago with a used one I had just cleaned up, but the problem was there before and after the swap, so I don't think this is it, but I'll do a diagnostic on the newly installed alternator anyway. At this rate I should have every part in the car replaced by the time I figure out what this is.

Also thanks Trochoid, the cables certainly should be suspect, but actually they are in very good shape with no signs of corrosion and now, given that my shiny new and expensive replacement cable ends aren't doing any better, I'm guessing the el cheepo autozone ones I replaced weren't to blame either.

I'd sure like to know what the actual engine temperature is during these episodes so I'll put my second temp guage and sensor in this weekend:





But in any event it looks like I'm back to looking for grounds, misbehaving belts and some of the other things mentioned by the RX-7 gurus in this post. I'll go back to the first recommendation and run through them again.

At least I have lots of things to try, thanks for the suggestions folks.

Ray

dj55b

iTrader: (2)

This may be worth a shot too ... check how good your battery is too ... maybe its not holding a charge, but i would assume that while driving the alternator should provide all the power anyways.

Kentetsu

For a quick test for grounding issues, just run a wire from the negative terminal to any point on the engine...

I still think your belts are slipping though...