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Old 06-20-2016, 03:39 PM   #1
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Temperature warning light and buzzer

I've got a 87 Thomas/Chevy bus w Detroit diesel and an Allison automatic tranny. Recently experiencing a temperature warning light issue. It had been intermittent (when over bumps and things) now it's been constantly on. Actual temperature gauge works and the temperature reads fine as far as we can tell. I believe it's just a simple connection issue or a bad sensor, but id love some input from thr community here.

Thanks in advance for your help
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Old 06-20-2016, 03:44 PM   #2
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Location: Richmond Virginia
Posts: 534
Year: 1984
Engine: 366 Big block Chevy! :) w/ Stick shift

Are the Warning light and buzzer together? Always a buzz when the light appears?
I ask because i know the park brake has a buzzer, so not to drive when it is applied.

Good luck!
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Old 06-20-2016, 04:27 PM   #3
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Location: North carolina
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Year: 1986
Coachwork: Thomas
Chassis: Ford
Engine: Detroit 8.2
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There is not always a buzzer to go with every warning light and there is not a warning light to go with every buzzer.
Krizpy the wiring diagrams I have only cover the Thomas body wiring which will help in the bus but don't cover the platform/engine/tranny wiring.
Find and trace your thermostat wiring connections and replace/inspect connections as you go or just disconnect until you can if you know your temp. Guage is correct?
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Old 06-20-2016, 04:48 PM   #4
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It's both light and buzzer coming on and it's not the brake

It had been a quick short bleep every now and then over bumps and things. Then more consistently. Now its a regular on at start and will shut off temporarily when going over bumps, lol... so we kinda figure it's just faulty wiring somewhere.

The guage seems to work, as it registers as the engine warms up and further when we actually get moving.. and maintains a consistent temp when driven. So, we figure it works. (I figure if the guage was goofed up that the warning would trigger as the temperature rose, not constantly as it is now.)


Recently made a trip from Tampa to Orlando successfully, but not without major issues on the way back.

Previous owner had linked 2 hoses together that ran from the tranny to the radiator. Damned thing blew st the joint almost as soon as we hit the interstate heading back.

We managed to get that all back together and get her home, but what a ckusterfkc.

Hoping that's not causing the warning as it had been intermittently sounding before the Orlando trip, but who knows. I dont have a guage for transmission temp, so... ? :/
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Old 06-20-2016, 05:24 PM   #5
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Year: 1946
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Chassis: 1- 1/2 ton
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A tranny temp gauge is really a necessity. High temps can destroy the fluid in just a few heartbeats. Then the tranny goes south.
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Old 06-20-2016, 05:26 PM   #6
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Location: Winlcok, WA
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Most temperature buzzers and lights work by going to ground when a specified temperature has been reached.

It is possible that the wire from the sender has been rubbed raw somewhere that allows it to go to ground somewhere yes causing your light and buzzer to go off.

Low oil lights and buzzers work the opposite way--no pressure the sender goes to ground. Once a specified pressure is reached the sender cuts out the ground and the light and buzzer go off.

The only way to know for sure what is going on is two fold.

First, every bus convertor needs to invest in an infrared thermometer. They are really handy when it comes time to accurately gauge temperatures. When a gauge says one thing and a light and buzzer say something different it is hard sometimes to know which one is lying unless you have a tool that can determine which one is lying.

Second, if in truth you are not overheating you are going to have to find the sender and the wire going from the sender to the light/buzzer. Either the sender is bad or the wire is grounding out somewhere. To find out for sure you are going to have to find all of the wire and the sender.

If the light and buzzer are OEM factory equipment finding the correct sender may be a problem. It might be easier to install an aftermarket unit if it is an OEM factory part.

If it an aftermarket light and buzzer like what Stewart-Warner used for many years it shouldn't be a problem finding a new correct sender.
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