ray green

iTrader: (14)

We'll I'm hoping you guys are a lot smarter than me and can figure out why my headlights make my stock temp gauge wander up into the overtemp zone when I put an electrical load on by turning on the head lights, heater fan or radio. The symptoms were described in this earlier post that got too long to be useful:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/my-headlights-make-my-car-overheat-633150/

What I now know:

1. The car isn't really overheating, since my newly installed mechanical temp gauge stays steady at 180 degrees when the stock electrical gauge starts to wander.

2. The response on the temp gauge is slow, it takes a minute or two to fully readjust to it's new hot temp. Then if you turn off the headlights, it slowly comes back down closer to normal.

3. There is a 1 volt drop across the battery (read with a volt meter) that also shows up on the stock voltmeter, they both go from 13 volts down to around 12 volts when a load (ie the headlights) is introduced. I don't see this voltage drop on my other GSLs, so it seems to be specifically related to the problem.

4. It's not the battery connections or the ground connections running from the battery to the starter bolt - I've totally redone these with no effect.

5. It doesn't seem to be the alternator, I've swapped in three different units, all of which worked fine before. Also the belt to the alternator is showing no signs of slipping and has be changed and tightened several times, all with no effect.

6. Possibly related to this problem is that the car has been running lean, with the plugs showing white after a week or two. This is actually a good thing because it has cut down on my exhaust emissions (ie, the yellow-brown stain that accumulates over the exhaust pipe) and the car still runs great out on the highway, where I do most of my driving and the gas mileage hasn't been effected. Still I'd like to figure this one out too and if they are related that would be great.

My last resort is to rip out the gauge cluster and replace it, but first, am I missing something? Like a voltage regulator or something like that? I never was that good at electricity.

Thanks!
Ray

DriveFast7

iTrader: (1)

1 volt drop isn't bad considering the headlights and parking lites are all being lit up. How about running an 8 gauge cable from + battery terminal to + output on alternator. That's really helped me in the past. I also replaced the stock + output from alternator to fuse box, mine was crispy. Also helped. As did adding grounds for bat, engine and replacing the ground from muffler to body.

Doubt low voltage would burn more gas.

I unplugged the stocker water temp gauge on my REPU, just use an autometer one. More reliable and actually gives a temp number.

Myki-Rx7

My GSL is currently reading overheating 100% of the time... Warm up is fine, but once it's running it goes past the H- got a temp sending unit waiting at mazdas and more for me. Are you sure it's actually running that hot? Mine started reading about there at first, and as it died more it read hotter and hotter, but when I inspected the radiator water and hosing (top and bottom) it kept nice and cool, hot water then cool water- as it should...

Just my two cents, the unit costs about 50 bucks, and I think you can install it relatively easily. Good luck bub.

KansasCityREPU

iTrader: (9)

Could it be a faulty temp sensor?

ray green

iTrader: (14)

I should have mentioned, I've swapped in a different temp sensor unit from a car that had no problems, that didn't fix it either. Both the original and replacement sensors looked to be in good shape, no indication they were worn or bad.

Also, to be more precise, the voltage drop is more like 1.5 volts, from around 13.5 volts to 12.0 volts, read both on the stock dash volt meter and with a pocket volt meter. I've compared this to the readings on another GSL I have and I get the same 13.5 volts without a load, but only a very slight voltage drop when I fully load the electrical system by turning everything on. So I think this voltage drop has something to do with it.

You can see pictures of the actual stock temp gauge readings with and without the headlights on the post that I linked above, it is very consistent and hasn't changed since I first noticed this happening back in early December. And as I mentioned, when this is happening my aftermarket mechanical gauge reads a steady 180 degrees, so I don't think there is any actual temp increase.

Also, while this doesn't necessarily rule anything out, all my wiring is in very good shape, nothing badly warn and no history of electrical problems, burn outs or replacements. In fact everything on the car works very well, including the electric antennae, rear wiper and washer, windows, everything. Except the temp gauge wanders up to the two thirds mark when I put any significant load on the battery/alternator.

The help is much appreciated, I sure would like to put this one to rest.

Rx-7Doctor

iTrader: (13)

Ray, I am working on diagnosing your problem. However it is going to be trial and error with a few things. I need you to do me a favor and swap out the fuseable links for the headlamps and power. All 3 of them from your non mal-functioning vehicle to the mal-functioning one. I'll explain later when I get feedback from you after you swap them and see if there is any change in the mal-functioning vehicle.

Also check and make sure that the small power wire to the fusable link box is tight. Meaning that the securing screw is not loose. Also make sure that wire is not corroded or frayed anywhere.

Thanks.

trochoid

iTrader: (6)

The sender works on resistance. Increasing the load increases the resistance as shown by the voltage drop. Finding where the extra resistance is may be difficult. Doc has a good place to start. Out of curiosity, if you use the high beams, does the temp gauge read even higher?

ray green

iTrader: (14)

Thanks Guys, I'll try these tests later today and get back to you, the answer to this has got to be interesting, whatever it is.

twinkletoes

iTrader: (17)

Hope you get this worked out Ray, Its been a weird one. Well, I kinda have the same thing as far as volt dropage. I'm usually at 14 volts on the guage and when I turn on cornerlights, then the headlight, I lose some voltage, then so forth with radio and ac. Never gets below 13 though. But, its noticeable, but not like yours. Goodluck.

mikey D

My car used to do that. It was the worst thing as I thought it was ACTUALLY overheating.

do your lights dim also depending on high or low rpm?


First thing to do is add a ground from the Battery to the Chassis.
Grounding to the starter bolt isnt the best place.
Put one to the chassis and one to the engine.

there are other grounds in the stock harness you should clean up also.

then your problem will go away.

ray green

iTrader: (14)

OK, I've been working on the RX-7 most of the afternoon. I cleaned up and replaced the fusible links (except the one in the steering column). Also I cleaned up the connector box and redid the lead. The links and connections were dirty but not corroded. Here's a photo after they were cleaned up:



Unfortunately these changes didn't make any difference, the temp gauge still creeps up at 4000 rpm with an electrical load on. Also the voltmeter is still reading down around 12 V instead of 13.5, where it belongs.

While I was at it, I redid all the electrical connections to the battery, coils, ignitors and distributor, but of course this didn't make any difference in the temp gauge problem either.

But I discovered something that I think might be the cause, the chassis ground between the battery and starter. Again dirty, but no corrosion. Maybe this is the problem. The chassis ground is hard to get to on my car because of AC and PS, so I decided this would be a good day to get rid of that stuff, along with the cruise control, since I haven't been using these accessories.

It was getting dark by the time I had all that plumbing, wiring and hardware pulled out and a return tube manufactured for the steering box, so I didn't have time to remount the chassis ground. So I'll do it tomorrow, I hope that's it but if not I'll be looking for the next ground to redo, I suppose. At least the engine bay is going to look a lot cleaner and I'll be about 50 lbs. lighter.

Directfreak

iTrader: (2)

Run an extra ground wire from your battery to the engine itself, and to the frame.
Without good grounds, the + voltage wont be able to go through.

ray green

iTrader: (14)

Thanks Directfreak, I will do that if cleaning up the regular ones doesn't work after I've cleaned them up.

Directfreak

iTrader: (2)

Wiring is a strange thing.. The current ground wires may look and feel perfect,
but still not have the bandwith needed of a new wire. Try adding a ground as
I previously stated, if cleaning the current ones does not work.

GavinJuice

to check if you have a good ground wire, read the voltage from one end of the wire to the other. If the wire is good and not corroded, you should read OV or very low. If you got a bum wire or connection your going to read those few volts your missing when you apply your load.

read this http://www.aaroncake.net/RX-7/grounding.htm it's for second gens, but the same concept applies and he does an awesome job explaining.

ray green

iTrader: (14)

OK, it turned out to be the chassis ground. Thanks to all you guys who suggested this in the first place. Once I got all the stuff out of the way I cleaned it up, put everything back together and the temp gauge pegs steady at 1/4 on the gauge, lower than it's been since I bought the car more than a year ago. And the volt gauge barely flickers when I load it up with all the electical in the car, just like it ought to be. Life is good.

I could say that I wish I'd tried the chassis ground before the other two grounds and all the other stuff I ended up doing. But with the AC and PS in the way, the chassis ground was hard to get to. And it didn't look like it was in bad shape. I guess it had just enough corrosion to cause these weird symptoms over the last year.

But in the end, it turned out to be a good deal. I've completely redone my engine compartment, gotten rid of a bunch of clutter I wasn't using and even have an aftermarket mechanical gauge so I always know what temp it really is.

I'll post some pics tomorrow when there's some sun, it looks great under the hood.

Ray

trochoid

iTrader: (6)

Congrats Ray, I'm glad you have finally resolved this issue. These are the ones that make working on our cars fun, in a frustrating sort of way. Most members don't know it, but there are 2 grounds that often get overlooked/removed. There should be one between the firewall and engine/tranny and another braided ground strap from the muffler to the chassis.

trochoid

iTrader: (6)

congrats on finally resolving this issue Ray. These type of problems are what make working on 7s fun, in a frustrating sort of way, lol. Most members don't know that there are ground straps from the firewall to the engine/tranny and another braided one from the muffler to the chassis. I always suspected it was a ground issue because the temp gauge works on resistance. Without good grounds, the entire electrical system can suffer from increased resistance.

What surprises me is that the other resistance based gauges didn't show errors too.

ray green

iTrader: (14)

I'll post the pictures of the responsible ground tomorrow so that all will know. That's one mean little ground in there, caused me a lot of concern and aggrevation.

What do you mean, "the other resistance based gauges"? The fuel gauge has been more or less normal, but with the price of gas approaching $3.00 a gallon, I swear it's been acting a little squirrily.

The tach and speedo seem to be doing their normal thing howerver, reading too high for the speed limit.

Rx-7Doctor

iTrader: (13)

Wiring is one of the most overlooked causes of diagnostic problems. That's why I started you on the path of the fuseable links and power supply to them based on the info I gathered from the wiring diagram.
The oil pressure was not affected because it is a totally different type of sender unit and the fuel tank sender is not tied to that temp gauge circuit and gets its ground differently.
What is common in diagnostics involving running problems with Fuel injection engines is what is refered to as a wiggle test. Meaning that you go thru the suspected problem components and wiggle and test the wiring in that area. I have found these type of problems when diagnosing problems with the SE.

As far as the mentioning of adding grounds. I am not a big advocate of this. I believe that it is a bypass of an existing problem. A problem that can be solved by repairing or replacing the existing grounds.
Remember that the wiring and ground connections on our vehicles are very old and corrosion is common. It's a matter of fixing this corrosion to restore the electrical system back to it's former self.
More is not always better. Replacing the existing grounds with ones of larger diameter is not a bad idea but adding them is IMHO not necessary.

trochoid

iTrader: (6)

Resistance based gauges. The sending unit for fuel level is based on resistance, (ohms), as it has a fine wire wound around a bar and a tab on the end of the float arm moves across this winding, shortening or lengthening the amount of wire the current must pass though to complete the circuit. As the resistance, (ohms), increases/decreases, the signal sent to the gauge changes. The Oil pressure sender works on resistance, but it's changed by a diaphragm. Not sure what method of resistance the temp gauge works off of.

The oil, water temp and fuel gauges themselves work off of the same wire wrapped bar and pickup tab. If you have a spare/junk fuel sending unit and dash gauges, take them apart for a visual reference.

ray green

iTrader: (14)

This is great, I'm not only getting my engine bay all cleaned up and my gauges fixed, I'm learning about how the work too! Thanks Doc and Trochoid.

Here's a picture of the offending ground, after I got it cleaned up:



I also have a movie of the gauges working perfectly, it's fantastic, a must see. Can anybody tell me how to post movies?

trochoid

iTrader: (6)

Post your movie on You tube and provide the link to them.

ray green

iTrader: (14)

It's hard to keep up with technology these days, I'll give it a try on Monday (away for the weekend, going to Mississippi, they don't have internet there).

Thanks!

Directfreak

iTrader: (2)

Exactly - but you are referring to a 20+ year old car, that you are trying to keep stock.

In today's world, with all the new electronics, fog lights, stereos, turbos, and other things that we add to the car (which the stock ground wires arent designed to handle) - then a few good extra grounds will definately help.