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#1 Old 12-23-2009, 04:37 PM
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Temp Gauge Up and Down

93 pickup, 4x4, 22re, 4cyl. 330,000 km's.

when driving on the highway, engine temp will go up for about 30 seconds and drop and be fine until the next time I start it up again.

very weird, any ideas on what this could be.

also, this is in the middle of winter when it's about -20 out.
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#2 Old 12-23-2009, 04:51 PM
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You mean it will shoot up and go back to normal after it has been warmed up to operating temp for a while?
Or while it is warming up after a cold start?
The second would be pretty normal overshoot, more obvious cause it's so cold.

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#3 Old 12-23-2009, 05:25 PM
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warmed up for about 10 minutes, 5-10 minutes on the highway and it will shoot up beyond the red zone. stay there for about 30 secs and return to normal temps.
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#4 Old 12-23-2009, 05:51 PM
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Probably your water temerature sensor is bad. Could even be a loose connection there at the sensor.
It's a simple/cheap fix.
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#5 Old 12-23-2009, 08:41 PM
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does this happen only if the heater is on?
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#6 Old 12-23-2009, 09:18 PM
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warmed up for about 10 minutes, 5-10 minutes on the highway and it will shoot up beyond the red zone. stay there for about 30 secs and return to normal temps.
A bad sensor or connection would not likely cause the same a recurrent problem like that.
Again, that sounds normal, especially in that low a temp. It happens even more so when the heater is ON, which it would be @ -20*. When the coolant goes through the heater core it gets cooled off enough that when it returns the thermostat closes again momentairly. So the temperature goes up and the thermostat opens again, and then it goes back down. If it went up and stayed up you might begin to be concerned.

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#7 Old 12-23-2009, 09:55 PM
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Actually a bad sensor can cause that problem. I had the same exact problem with the gauge going all the way to hot to normal and everything in between. I pulled over thinking I was over heating. I popped the hood, no gurgling sounds and the hoses didn't feel any hotter than normal. I changed the sensor the next day, no problems since. That was 3 , maybe 4 years ago.
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#8 Old 12-23-2009, 10:27 PM
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Yes, but the OP stated it occurred under one specific circumstance. Not everything in between, which could indicate a bad sensor or connection.

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#9 Old 12-24-2009, 01:00 PM
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this sounds a lot to me like an old thermostat is sticking shut.

My truck does this too, it is a 94 but same truck as the original poster.

I am not that concerned (b/c i know to watch my temp gauge) but when i flush my coolant next time I am going to replace the thermostat.

My understanding is that this a very common condition (at least here in our cold climate). The vehicle starts cold and the thermostat is closed, but once the engine coolant hits 190 F (180 F for the v6) the t-stat should open immediately, but sometimes it takes a bit longer due to sticking shut, so the engine coolant gets hotter than normal and the temp gauge head towards the red. Then a minute or two later (in my case) the temp gauge drops b/c the thermostat has finally opened, and from then on no problems.

I would watch your temp gauge and make sure it doesn't hit the red for too long before dropping and you are probably fine. I've only hit the red once but I stopped the truck when i saw it and waited for it to drop before driving again.

I am 90% sure that this is a t-stat problem...could be the temperature sender but doesn't seem to fit the symptoms.

This also happens in my truck during the summer time, i don't think it's unique to cold weather, and it doesn't happen everytime, sometimes the t-stat doesn't stick and sometimes it does.


Flush your coolant if you haven't in 2 or 3 years and replace the thermostat.

i'm almost willing to guarantee that this will fix the problem.
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#10 Old 12-24-2009, 01:22 PM
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and since i just got up to speed on the difference between the temperature SENDER and temperature SENSOR on these trucks (with the 22re at least) i will clarify something.


The temperature gauge is controled by the temp. SENDER. It is located in between the EFI unit and the engine valve cover, and is positioned vertically. It has only 1 electrode and only talks to the temp gauge on the dash.


The engine coolant temperature SENSOR sits in front of the fuel injection unit directly underneath the air intake and is positioned horizontally, (is the one on the R hand side when looking from the front of the vehicle, on the L is the start injector time switch). This sensor has 2 electrodes b/c it must get a signal from the ECU, pass this through its thermistor, and return the signal to the ECU.

http://personal.utulsa.edu/~nathan-b...36electron.pdf

I had this ECT sensor go bad in my truck recently and it made all kinds of hellaciously intermittent timing problems for me that I finally resolved by replacing this sensor.


Anyhow, I don't think either the sensor or sender is causing your problem Patty, but wanted to clarify this terminology.

Last edited by andweav; 12-24-2009 at 01:51 PM.
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#11 Old 02-17-2010, 09:42 AM
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Ugh, thought we had this solved yesterday, and today it happened again.

Replaced t-stat, "bleed" the system with coolant.

Still hits the red for 30 seconds, drops down to normal and remains there until I start the truck up again. Whether it be 2 mins later or an hour.

Someone, please. My mechanic and I can neither pinpoint this down, and he has been a yota man for 20 years.

Please help my baby.
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#12 Old 02-17-2010, 10:27 AM
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Not that it couldn't be a sender, that's not how they usually fail.

Get and infrared temp gun and check the actual temp at the intake manifold just below the t-stat.

Does the temp spike? No, test the temp gauge circuit.

Yes, try a factory t-stat. if that don't work check for CO2 in the coolant (indicates a leaking head gasket).

Don't talk about it, Just do it!

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#13 Old 02-17-2010, 10:32 AM
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it appears it is not circulating the coolant? rad stays cold while head is warm to the touch after startup. we bleed the system and had it vice versa for all of yesterday. now, this morning it is back to the problem. we had the temp gun on the plugs and it was reading just beow 500 degrees, which is very hot compared to the normal ~250ish.
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#14 Old 02-17-2010, 05:44 PM
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any ideas?

water pump maybe? appears to have never been replaced.

would that explain the surge until the motor gets hot enough to circulate the coolant itself, making the t-stat eventually open? then because i turn it off, t-stat closes and has to technically overheat again until it will open and circulate again.

make sense?
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#15 Old 02-18-2010, 04:02 PM
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replaced water pump, still doing it.

really confusing as these aren't typical signs of the head gasket going.

any hlep?
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