On the road w/temp gauge

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May 31, 2003
Started out on the trip to mexico today - towing a boat. The temp guage either reads normal or just below red zone. I feel in the dark not knowing actual temperatures. I'm thinking of stopping and buying a temp guage.

Is there any easy place to install the sender on the engine?

If not easy, where would be least difficult and what would I need?

Any brand recommendations?

Currently east of San Diego on I8 heading to Arizona. This temp issue will become more critical getting into hotter air temps and mexico desert.

If I get a gauge with numbers, what is max safe operating temp?

Any idea what temp range I'm in between midway and just below red.?

Thanks much, guys. I'll check in a little later...

Ed (w/ wife and 9 year old son)

BTW, the Verizon Wireless air card in  the laptop is great. On at speeds exceeding DSL anywhere Verizon digital signal is available

Bill, thanks for the link. Read it just now while fueling. You wrote good info in that thread.

My AC is cutting out when the guage moves just slightly above center. Hope that isn't 220, because it goes to, as you said, about 1/16 of an inch below red.

Still wondering... what is max safe operating temp?


Ed...when you say "normal" or just below the red zone, has your 80 always ran there? I have a '94 (no difference in the motor) and it runs at horizon or a little bit below (sweep gauge). I know our gauges are different but there seems to be more leeway on my temp gauge. I have a friend who has a '94 and his runs in the same spot. I know you are on the road and this will not be important now but you can buy an aux. gauge pod from Jegs that fits the A-pillar. Just my .02 worth. Good luck!!!
I'm not sure I understand the question. Ideally, it is better to stay under boiling which is 212 F. I suppose you could say that is ideal but I think unrealistic since there are many conditions, altitude, towing, etc. that could lead to higher temps. It is not good for an engine to run hot consistently but is OK for temps to occasionally go up. To stay under the temperarure at which the engine would boil over is approx. 230 F. As you read in the thread Toyota has a built in Engine Coolant Temperature Cutoff Switch that comes in at at 226 F and shuts down the AC. If you are experiencing this AC shutdown you have problems as you are definately running too hot. (probably plugged rad) Are you boiling over? Loosing fluid? If your AC is shutting down and you are not boiling over you either have a defective Engine Coolant Temperature Cutoff Switch or you are sitting on the boil over fence.
FWIW, if you do boil over, and I should watch what I say, wait till engine cools, remove rad cap with a rag very carefully, have water/anti freeze ready, START engine, add water/antifreeze slowly, carefully watching for some blowback. Keep adding till full. If you add water to an engine that is not running you can crack the block/head. Hope this has been of some help.
"Normal" and "just below the red" - 2 different readings. Sorry, in my haste I didn't make that very clear.

Normal is horizon - right in the middle of the guage. If it's not there, it goes right to "just below the red". Nothing in between. It's one or the other.

Have you installed a numerical gauge? If so, where did you put the sender? My next project will definitel be an aux gauge. To put a temp alarm sender on a sailboat engine, I fabbed a T fitting out of 3 separate fittings. Cut, welded, and drilled. But it worked. As I recall, that was about a 4 day project.

Bill, sorry to you also for not being more clear. My concern is that all that my gauge tells me is that I am somewhere between C and H. When I am running near the red zone it would be nice to know what temp the engine is actually at.

The second part of the question refers to if I had an aux guage and knew the actual reading, what then would be the max safe temp I could run at. Your answer that refers to temporary and sustained temps makes sense.

I must have a defective A/C shut off because it's shut off point varies greatly. Sometimes it shuts down even when the guage is reading level horizon - its normal reading.

Haven't boiled over. Had a Toyota dealer cooling system flush in December; belts replaced and hoses inspected last Friday.
Your info has been, as usual, very helpful.



I'd have to agree 100% with what Bill has said. My gauge runs at just a hair below half-way and never exceeds that. One time it did go to the point you refer to as 1/16 below red, and it was due to a bad water pump (not very noticable since it was a slow leak, but it did eventually run the coolant level down). I would consider this to be an overheating situation since my temp gauge never actually went into the red, even though the coolant level was seriously low. FWIW, I don't think these gauges are reliable to tell you anything other than that the engine is running normally--it may never go into the red for all I know.

It's my belief that the heating cycle(s) caused by those episodes of hitting near the red zone are the cause of my head warping and my blowing a head gasket a little while back (about nine months after the water pump went). I'll add that putting a S/C on may have exacerbated the gasket problem, but I still think the warpage was the direct result of the overheating--the S/C just helped the weakened gasket blow out due to the increased pressures.

If your temps are going above normal, even while towing, I'd quickly start looking for the cure--perhaps a rad cleanout/rodding as suggested if that's where the problem is. Running hot will only do damage to the engine.

Good luck.

Sorry I was not clear about one thing. It is normal for the AC to cycle on and off. It is when the AC shuts down and blows VERY WARM AIR that the Engine Coolant Temperature Cutoff Switch has been activated at 226 F. I know it is tough on the road but if you look at page two of the link I posted you will see the gauge I used. To repeat it is a Greddy Metric temp gauge that I mounted on the DS US A pillar. I also included an aux large red light (seen in the picture) and a piezo buzzer. The alarm set point I use is 226 F. Wiring the alarms is a no brainer as Greddy provides an extra wire for aux. alarms. The sender is mounted in the engine block drain hole (not the best place) as I was afraid to remove the stock sender in case the ECU needed it. I could not find an unused hole in the head to use. Watch for an update on this from C-Dan in the future. If you are running 1/16 from red I will just guess and say that is about 218 F. I can't repost the picture of the gauge as I am having trouble with the site.
As Tom said overheats can cause head gasket failures.
Just out of curiousity have any of you that are having overheating problems tried Redline Watter Wetter? I have used this product in the past on cars that ran marginally hot and found it to work well. In the case of my old street/track car, it would tend to ping on warm days with super, the watter wetter would lower the temperature just enought to keep it from pinging. Redline claims up to a 30 degree drop in coolant temperature, I have seen more like 5-15 degrees, not a lot but it could be the difference between overheating and not.


Another option to installing a seperate temp gauge, since you apparently have a laptop and your truck is a 96, would be one of the computer based OBD2 monitors. It will give you a specific temp reading in degrees. I assume that it is reasonably accurate, since the computer uses the info for emission control and other functions.

I have one from OBD-2.com (no affiliation, just a satisfied customer) that works well. My gauge always sets at the midpoint as well, and according to the software, that is right around 187-194 deg F. Prices start at about $140 for a single interface. I paid $180 for mine, which has all three interfaces and works on all OBD2 compliant vehicles.

Bob Garrett
95 FZJ80
Shawnee, KS
I have experienced this same problem this past sunday,while towing my boat to a lake in a neighboring state....
Cruising on the interstate at 70 mph was no real problem,gauge at the middle like all none towing running,but some of the grades caused the tranny to kick down into 2nd(causing rpm over 4000+ and thats when the temp gauge would move slightly up above the "normal" horizontal....
the longer i was in 2nd gear the higher the temp would rise(never went into red though)always left me about a 1/4-1/8 before the red....

When we got to the lake there was a short hill that required 2nd gear and at low speed(<25 mph)the temp climbed towards the red but still never into the red..this lower vehicle speed put the temp gauge needle to within 1/16th of the red though..........

The temp always returned to "normal" horizontal position when the grade was completed or when the tranny shifted to 3rd and was no longer above 3000 rpm...

I always tow with the overdrive "off" and keep it there as it seems the engine would labor in 4th gear...is this correct?

Afterwards everything seems fine,truck runs/shifts great but i too do not like subjecting my truck to this abuse so, i am looking for a cheap tow vehicle!!!

Bob...The search for an OBD2 monitor is on!!! Thanks for the suggestion.

Doug...That's exactly what's happening, exacerbated by 45 miles of continous mountain driving between San Diego and Arizona. I've adjusted my driving style, speed, gear selection to whatever it takes to keep that little needle below the red zone. On the flats, it's 60 mph with a/c on and normal needle position.

As all have said, running hot is bad potatoes. The frustrating thing has been not knowing the actual temp the truck gets to just below the red.

Tom...I will definitely heed the warning of your experience as much as possible on this trip.

BTW, checked the coolant level after the truck sat all night and it's normal. Haven't boiled out any of the red stuff.

Any of you Arizona guys know where I might find the computer based ABD2 monitor in Phoenix or Tuscon?

Thanks all,


I thing the water wetter would be one way to forestall the inevitable cooling system repair that's needed, or to increase the operating range a little, but for all except very unusual setups (maybe Bill's? :D), I think trucks that are running anything but normal temps are flirting with danger.

The only reason a temp gauge should exceed the normal range (seems by most to be just below or right about the half-way point) is when the cooling capacity of the system has been exceeded, the thermostat is wide open, and you're just trying to balance the heat input vs the heat output. That's not a good place to be IMHO, and if I was seeing that, I'd be inclined to keep the speed/gearing at a point that I was in the middle of the temp gauge.

I realize I'm probably more paranoid about this than most others, but an ounce of prevention is worth about $4K in repairs :eek:

Alright! The forum comes through again. Bought an OBDII scanner. I never would have thought of that.

Since we got a late start this morning and I didn't want to rush through the directions, and since its flatland driving for now - I'll hook it up later.

One more question that will help save some time....Where is the OBDII connector in a '96?

:(Re: On the road w/temp gauge

Software based is a very cool idea. I looked at the site and the price of the software for a hand held is ~$500 :( That seems a bit rich?

Cheers, Hugh
In the dash fuse panel. Pull off the door and there you have it........ :D
I run Water Wetter. FWIW Water Wetter only affects the water portion of the water/anti-freeze mix. Here in the North we run at least a 50/50 mix so do not get the full benefit of the Water Wetter. In a warmer climate where the proportion of mix is less they would see a greater benefit.

Here is Bill's Greddy temp guage:


>> I realize I'm probably more paranoid about this than most others, <<

Most, but not everyone! You guys are giving me the creeps. I won't sleep tonight for sure. %#@& :D

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Check out www.obd-2.com. Under $200 for one that works on all OBDII vehicles. Less than $150 for Toyota only.

Bob Garrett
95 FZJ80
Shawnee, KS
Hooked up the OBDII scanner (thanks for pointing out the
connector, CDan).

The temp gauge needle stays at the horizon position while the readout shows from 208 to 221. Needle never moves during that range of temps. Then a very barely discernable movement up at 222. After 222 the needle jumps to the before-described position of about 1/16 inch below the red zone and stays there from 223 to 230! At 231 it jumps that 1/16' and just barely touches the red. Didn't push it beyond that.

No wonder that needle was driving me wacky...

It's nice to have hard data. Thanks, guys. On grades, I'm staying at 226 max. Toyota engineers call 232 or so the red zone, so maybe 226 during climbing will be OK. Only problem is, I got passed by a guy on a bicycle on the Interstate - Just kidding.

The scanner showed the intake air temp at 146 degrees. Rather warm under the bonnett, wouldn't you say?

Another readout showed the load factor, which could be interesting if there was some frame of reference.

I've been thinking how cool it would be to have an OBDII scanner readout where the clock is now in the dash.

Thanks again and Adios...into Mexico tomorrow.


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