[Sithross]

Hello,

I've recently purchased a 1989 Mazda B2600i, being the second one that I've owned.

The problem I'm having is that the coolant temperature gauge on the dash is not properly displaying temperature. After a few minutes of driving the gauge will move up the the very bottom line (cold) and not move past that.

I've purchased and replaced the coolant temperature sensor.

https://www.autozone.com/engine-management/coolant-temperature-sensor/p/duralast-coolant-temperature-sensor-su405/125898_0_0

But it did not help at all. After some searching I keep seeing another "Coolant temperature sensor/sender -gauge"

https://www.autozone.com/engine-management/coolant-temperature-sensor/p/duralast-temperature-switch-tu115/45261_0_0

But for the life of me cannot find where this sensor/sender is located, in any literature or diagram.

If anyone has any ideas where this second sensor/sender is located or any other advice on getting my temperature gauge to work, it would be greatly appreciated.

 

[Cussboy]

First thing - and no cost - would be to bleed ALL the air out of the cooling system. I have B2200, and tricky on these trucks. Jack up front end or park on severe uphill. Take off radiator cap, turn on heat, start engine, and keep adding 50/50 coolant until no more can be added; can take 20 minutes.

On my B2200, the sender for my gauge is on the cylinder head near the thermostat outlet pipe.

 

[Cussboy]

if you post the question about the location of the sender for the B2600i gauge on Mazda Pickup Trucks - Mazda Forum - Mazda Enthusiast Forums at least one member there has several B2600i and KNOWS exactly where that would be.

 

[tholman1051]

if you post the question about the location of the sender for the B2600i gauge on Mazda Pickup Trucks - Mazda Forum - Mazda Enthusiast Forums at least one member there has several B2600i and KNOWS exactly where that would be.

Did you check to see if thermostat was stuck open. This will cause engine to not fully warm up. Most thermostats are designed to fault in the open position

 

[Axel Breaker Earl]

The first link that you posted is the coolant sender/sensor for the ECU, not the dash temp gauge.

The second link that you posted is similar to the dash temp gauge (located on the side of the thermostat housing) but instead of a flat blade connection terminal, it should have a round pin connection terminal.......circled in red below.

 

[Cussboy]

The second link that you posted is similar to the dash temp gauge (located on the side of the thermostat housing) but instead of a flat blade connection terminal, it should have a round pin connection terminal.......circled in red below.

View attachment 10644

Sithross - Axel Breaker Earl knows a ton about thee trucks; he was the resource I was hoping would answer you.

Earl - the engine photo shows a circled sender that looks very much like the temperature sender in my 1988 B2200

https://www.oreillyauto.com/detail/c/import-direct-ignition/engine-cooling/coolant-temperature-sensor/ecb98b223aec/import-direct-ignition-1-terminal-temperature-sender-with-gauge/odi1/171372/v/a/17640/automotive-truck-1988-mazda-b2200?q=coolant+temperature+sensor%2Fsender%2Fswitch&pos=4

 

[Axel Breaker Earl]

Yes Cussboy, they are very similar......the B2600i sender has slightly larger diameter threads than the B2000/B2200 trucks.......otherwise they are alike.

 

[Sithross]

Thanks for all of the suggestions.

I believe I've narrowed it down to being the gauge/gears of the gauge itself.

I completely replaced the thermostat and did a full coolant change at that time. While I had the water pump open, I pulled both coolant sensors out of it and cleaned them. Then tested both of them in a bowl of hot water with a multimeter to ensure there was voltage change, indicating that they are functioning.

Once everything was put back together, I took it for a test drive. The gauge responded the same way it did before: Starting a bit below the bottom line of the gauge, and was just above the cool line when at operating temps. The only difference being that with the new thermostat it sits higher on the gauge, but that was expected due to it being a 192°F instead of the 180°F thermostat that was removed.

Leading me to believe that the problem is just that my gauge has skipped some teeth and thus is responding properly just in the wrong position on the gauge.

I'm going to go pull the gauge cluster out of my parts truck probably this weekend, as some practice and to have the spare part ready. Just incase it is easier to just swap them instead of trying to get the gauge back in the correct position.


Where the gauge sits when cold

Where the gauge use to sit at operating temp.

These are the two sensors that I checked and cleaned.

 

[Cussboy]

I believe I've narrowed it down to being the gauge/gears of the gauge itself.

Leading me to believe that the problem is just that my gauge has skipped some teeth and thus is responding properly just in the wrong position on the gauge.

I believe that there are no gears or teeth in the gauge part. If memory holds, most of these are coils of wire and the magnetism from the sender current causes them to deflect upward.

 

[Sithross]

I have a parts truck that when it was running (for a very short period of time), the gauges all worked well. I plan to go pull the gauge cluster out of the parts truck, as "practice" before taking apart the truck I'm driving. That way I can inspect the gauge cluster, to see how it functions and what might be the issue. At that point it might just be easier for me to swap thr one that was functioning well from the parts truck into my new truck.

 

[Cussboy]

I have a parts truck that when it was running (for a very short period of time), the gauges all worked well. I plan to go pull the gauge cluster out of the parts truck, as "practice" before taking apart the truck I'm driving.

I've pulled a few gauge clusters at the parts yard. R&R is pretty straightforward, hint is to release the speedometer cable clip in the engine compartment to provide enough slack to disconnect the cable from the cluster.

 

[roadace]

Do you have wrong fuel gauge readings too? The problem seems to be the voltage regulator (mechanical) built into the fuel gauge, supplying regulated voltage to both, the fuel gauge and coolant temp gauge. I had the same issue, displaying low temp despite being at normal (190 deg) operating temp and erratic fuel level gauge. Fixed it by gutting the orig. voltage regulator and replacing it with an $2.00 SMPS voltage regulator (Ebay).

 

[RS2600]

I have a parts truck that when it was running (for a very short period of time), the gauges all worked well. I plan to go pull the gauge cluster out of the parts truck, as "practice" before taking apart the truck I'm driving. That way I can inspect the gauge cluster, to see how it functions and what might be the issue. At that point it might just be easier for me to swap thr one that was functioning well from the parts truck into my new truck.

Hey there, any update on this problem?
Facing the same issue and wondering if you identified any issues in the gauge cluster.
I swapped my thermostat but not the sender yet.

 

[Ctech5440]

I own an 89 B2600i with 133k my temp gauge does the same thing and my fuel gauge will bounce if I hit a bump. It comes with age I guess

 

[RS2600]

I own an 89 B2600i with 133k my temp gauge does the same thing and my fuel gauge will bounce if I hit a bump. It comes with age I guess

Hey Ctech5440, the response of your fuel gauge makes sense. Given that the signal is retrieved by a float in your tank, if there is any play in that system, a bump may set off an erroneous signal which would then manifest as movement on your fuel gauge.
____

As an update per the original issue, re: minimal / no response of temperature gauge.

I found a quick check online to determine whether the fault here lies with the sender gauge or the instrument cluster itself.

Connect the sender unit to the negative terminal of your vehicle battery via a jumper wire. Walk to your cab and;

• if your temperature gauge jumps right up to FULL HOT, this means that the problem lies with the sender unit and not the cluster
• if your temperature gauge doesn't move, you have a faulty gauge/cluster

(This essentially bypasses the sender gauge (which acts as a variable resistor) and delivers current right to your cluster.]

Fortunately when I tried this, my temp gauge shot right up which meant the problem was isolated to my sender unit.

Ordered a new one.
Sender Unit PN for '88 B2600 (and probably other years): Standard Motor Products TS-160

Drained the fluid from my radiator via the drain cock at the bottom. *Once you turn the drain-cock it will flow out and eventually stop. You will need to pull the top radiator cap off to let it vent. I prefer this order so you don't just start bleeding all the fluid.
I only drained enough to get it below the delivery hose at the top of the radiator.
Placed a catch basin below the sender gauge to prevent a mess and save the coolant since it was mostly fresh.
Got a 17 mm wrench on the sender and removed it.
Noticed the lead tab had mostly cracked off which explains the lack of signal / continuity. Not sure what would have caused this type of failure.

Installed and torqued the new unit (I did not use teflon tape to ensure the sender unit was grounded to the block)
Hooked the new unit up.
Poured the salvaged coolant back in (close that drain-cock first!)
Took the truck for a drive and within 5 minutes the cluster was reading nominal temperature.

(yes I snapped a quick pic while I was driving. I was excited that after months of not moving it finally worked.)

Success.

 

[Cussboy]

Success.

Great !!!

Poured the salvaged coolant back in (close that drain-cock first!)
Took the truck for a drive and without 5 minutes the cluster was reading nominal temperature.

Good. Be sure to bleed ALL the air out of your cooling system though !