Normski

My rheostat on my 88 v-6, 4 Runner is getting warm to touch at the alum. mounting block where it meets the plastic on the "dash" just below the plastic knob. This happened a couple years back and I removed and cleaned it and it seemed to do the job till now. I cleaned again and not fixed. Does the rheostat go bad? looks like there is not much to break on them or maybe another issue?

91Toyota

what is a rheostat???

kornhuskerwizard

you mean the knob that adjusts your interior dash lights intensity?? get a different one and see what happens, a rheostat is a adjustable switch that changes resistance on a circuit, kind of like a dimmer on your ceiling fan light at home...

Normski

Ok, I have done a little diagnosing and nothing. I bought a different rheostat at the junkyard put it in, cleaned and checked the ground on the driver side for the rheostat, cleaned the batt. terminals and ground wires at the block and fender, checked and cleaned fuses, unplugged my stereo (aftermarket but shouln't matter), took to 2 different auto stores for alt. batt. checking and both said ok, and still the rheostat gets hot at abt. 40min. to 1 hr lights on. My rear defog does not work but the light on the dash for it comes on (related or not??).

Question is could someone guide me in a direction to look at next. What could be doing this or is this normal? I now just switch the dash lights off till rheo cools down some and go about that way for now.

1988 v-6 3.0 man. trans. SR5 pwr windows/ac No mods just Walmart fog lights, sony stereo not plugged in for now.

limon32

Can you get at the wiring to it easily? If so i'd run it for a while maybe 30 min. but before the rheostat gets real hot check for heating in the wiring. Copper is a great heat transfer material, if your wiring is failing it may be heating and consequently heating the rheostat. Just a thought...

drew303

Just curious how you actually discovered it was hot at all? I havent touched that thing in probably years LOL

I'm wondering if something isnt tied into that ground (that is what the rheostat is wired to.. everything [that is suppost to be] is grounded to it, it interupts the ground) ... And whatever said item is wired to it is trying to pull amperage..which would cause the heating up.

The low volt/amp lights (that is ALL that it's suppost to be grounding) shouldnt cause it to heat up.

You didnt ground your stereo to the wrong ground in the dash by chance? ... its a thought.

Normski

Wish I never checked it either. I will try to see if the wires start to heat up first. I do know that some of the heat is from my heater itself the duct work is close to the rheostat and in the winter it is on, but that just makes things warm not hot.

The stereo is unplugged because of just that if it was by some chance wired wrong, I did not want it tied into the rheo, read that info on here that is why I disconnected it for now. If it was wrong ground shouldn't it "fix" itself if disconnected nothing to ground wrong if it isn't there.

Normski

Today I did get a couple of minutes to ,feel for temp of wires. At about 1/2 hour park lights on, the rheostat got warm but it didn't feel as if the wires were as warm as the aluminum housing. The wires do have insulating wrapping around them but didn't feel as hot. There was a little more heat at the base were it plugs in to the rheostat however yota design really has the couplers protected so I could not really touch the contacts just the plastic around it.

If just the rheostat gets hot is that a bad rheo?? I have a dmm should I be able to see if it is ok?? Rear defog doesn't work could it be pulling current anyway even if the switch for it is not on?? Is the rear defog (rear winow) in the rheostat loop??

What other grounds should I check? radio unplugged, no need to check that cleaned and checked rheo ground on dr side fuse panel side??

myyota

Its normal for the rheostat to get warm, because its basicly an adjustable resistor.

Normski

That does make sense to some degree no pun intended, but after 45min. to an hour I can't even touch it for more than a couple of seconds. It gets really hot. Is that "normal"?

iamsuperbleeder

well resisters do get pretty darn hot... I remember when I installed the in-line resisters when putting LED's in my turn signals; the instructions clearly said "Caution! Resister gets hot! Keep away from plastics and flamable materials", or something to that extent


Is it still functioning properly? Do the dash lights dim like they are suppose to? I have a suspision that it might be normal, but considering the rheostat is basically inside the dash, I would have a hard time touching mine to tell if it's hot

Normski

The unit works ok dash lights dim and all just hot. The older trucks "88" have a alum washer on the outside of the dash that holds the rheo in place so the heat is transfered to it, and the rheostat is only a finger away to reach under. I was going to see if my friends 00 taco gets hot but it is buried in deep also.

limon32

When you say that it works, do the dash lights get bright when you turn it up? Excessive heating is caused by greater than designed resistance which means that its breaking down internally. If the dash lights still get brigh, i'd say its "normal" but likely to fail soon. If they don't get bright i'd replace it.

The wires NOT heating up is a good thing, i was wondering if you had some corroded wires and the heat was transfering out to the stat but I don't think thats the case. Don't worry about your radio or grounds, there not the problem, nor is your rear defrost.

thefreqofnature

I have an 88 V-6 4Runner and the dimmer never gets hot and I do use it from time to time. I'd say somethings wrong. Sorry I can be more helpfull.

InternetRoadkill

The amount of heat at the rheostat is going to vary depending on the amount of dimming taking place. You may want to locate the electronic dimmer which was used in later years.

Normski

To start thanks for the replies.
The stat works "normal" meaning yes dash lights get bright and dim with the twist of the knob, however the heat intensity stays hot regardless of if on dim setting or all the way bright. I also thought that if turned lower the stat should have a little less heat, and it should however??

Do you think the stat is breaking down inside?? I could buy a new one at this point little spendy but has to be done, plus now it drives me crazy knowing it is overheating.

Do you know where the wires go once they leave the rheostat?, maybe I should check the other end first before the purchase of a new stat.
Do wires naturally break down and draw more current over time? Should I put a new wires in?

Anyway I will be putting in a new master clutch cylinder (whole different project but I still love my yota) so I will be under there.

I will keep posting on my progress maybe usefull to others.

milehigheric

master clutch cylinder is in the engine compartment not under the dash lol?

Pull the stat, disconnect it from the circuit and do a resistance test with a DMM for both fully dim and fully not dimmed (?). Toyota should have a resistance range for the stat if not maybe you can persuade someone that has a 'normal' stat to do a cross check for you.

The only cause I can think of is incorrect bulbs in the dash or Illum circuit, causing excess current to flow...either way the circuit is fused so your not risking loom damage in any form. Personally I wouldn't worry about the problem...stats by nature should get hot. The excess energy is radiated as heat to allow dimming to be possible. If you start blowing fuses or get a whiff of that burning wire smell then I would look into it further.

And no...wires do not have an INCREASE in current capacity (or flow) as they age. If anything current capability will decrease...Play around with the formula V=IR. As resistance increases (as it does with age, albeit a small amount) current flow actually decreases... These sort of issues usually occurs in splices where corrosion takes hold and can lead to all sorts of funny little problems.

Another little test you can do is current draw for both hardwired (stat not installed and circuit connected to the lights) and with the stat connected. Get your baseline reading for an unobstructed (bulb draw only circuit) and compare it to a reading made when the rheostat is installed but in its fully lit position. If there is a large difference in current draw then the stat may be failing internally.

Normski

Thanks that gives me alot to play around with, also nice to know not gonna really do any damage.

PhenomYota

milehigheric - Yes, V=IR and with age the resistance does increase in wiring, and it is true that this will lead to less current flow, but it higher resistance leads to a larger amount of voltage drop across that particular area. Larger voltage drop across that specific area would cause more heat. Like an electric heater. Even with that being said, I highly doubt the problem is bad wiring.

If you pull your rheostat out you will find a lot more than an adjustable resistor inside the switch housing, even though that is "essentially" what it does. There is an entire circuit inside the switch housing that includes resistors, transistors, and capacitors. There could be a problem with one of the other components on that circuitboard than just the switch. Mine has recently gone "bad" and left me with no dash lights. I have currently bypassed my switch altogether and am trying to find the correct switch replacemtn. Hope this helps!