Coolant Temp Gauge Problem

08 Tacoma 205,000miles

Recently started having a “problem” with my coolant temp gauge. I start my truck and let it warm to about quarter way up the gauge then start driving. When I give it gas the needle will start falling to “cold” and when I let off the gas it will start to raise again. Seems like the needle is a little higher than normal when driving too until I let off the gas again. Heat and A/C both work great. Any help would be appreciated. Thanks.

 

I don't know what the problem is but I would take a look at the alternators output (volts while running) at various engine RPM's. Good luck.

 

Anyone?

 

I'd start looking to see if it's the gauge (unlikely, IMO) or something else in the cooling system. Perhaps a stuck or failed t-stat?

Ya gotta confirm the gauge data is right or wrong before drawing any conclusions.

 

Have you done any work to the coolant system recently? The issue could be an air pocket in the engine.Park uphill and warm up the engine with the radiator cap off and see if you can burp the air out.

The sensor in the engine is not designed to read air temperature so when the air pocket is on the sensor the reading drops.

 

I’d use an OBD2 scanner with live data to compare the actual engine coolant temps to what the gauge is displaying, best to have a passenger to monitor this if you’re going to be the one driving.

I’m dealing with a fuel gauge issue that I’ve diagnosed extensively and I believe I have a bad instrument cluster, 206,000 on my truck.

A brand new cluster from Toyota is about $360 for my 2005, but there are also instrument cluster repair shops that will fix your cluster if you send it to them. A google search will give you a whole list of options if your temps prove to be stable and you determine that the cluster is at fault.

 

Nothing has been done to coolant system since I bought the truck 24k miles ago.

 

My fuel gauge is all over the place too. Never actually know when the tank is empty so I just fill up every 200 miles. That has been the only gauge problem I've had. I think im onto it being the T stat though because yesterday I found if I dont run the heat or air when warming my truck up it gets to operating temp much faster.

 

@Scalleywag was the fuel gauge itself the issue or was it the sending unit?

 

I’ve gone through two replacement sending units and traced all the wiring from the pump connector to the dash. My current sending unit is a brand new OEM Denso that was bought direct from Toyota. No change to the indication error.

I cleaned every ground I could find thinking maybe I had a corrosion issue.

The only two items that are left are the cluster and the Body ECU. I really think it’s the cluster as everything else works perfectly, including every other gauge on the truck.

I can afford a new cluster but I’d be sick to spend $360 and that not fix it. The Body-ECU is over $700; so like most on the forums, for now I’m using the odometer and scangauge II.

I’d love to find someone nearby (Triad area NC)with a 4x4 V6 6spd and a working fuel gauge that would let me swap the clusters and see if the problem follows the truck or the cluster.

I think there are a lot of folks on here with janky fuel gauges, as many people as report running out of fuel at 1/8-1/4 of a tank I think the root issue is relatively common.

 

can you elaborate a little more on what exactly your fuel gauge is doing?

 

When I bought the truck the fuel gauge was slammed at the bottom with the gas light on. Guy said it always sits there. Well first fill up and it showed it was full. Then after 100 miles it went to quarter tank and so on. Every time I started the truck within the first few weeks of ownership the needle was in a new spot. Nowadays 50 miles after refuel it starts to drop but I can still never get an accurate reading.

 

I'ma thinking.... Is it possible to use a battery and potentiometer to test the input to the gauge itself sitting on a table or a bench.

@Jimmyh might you have drawings for the cluster and the gauge (s) inputs?

 

Not certain about the temp gauge but Toyota lists a test procedure for the fuel gauge that is a simple key on with and without a jumper to test the gauge function. Naturally my truck passed that needle swing text but the gauge still isn’t right.

 

To your knowledge has any wiring been modified on your truck?

 

As far as I know everything is original and wiring hasnt been messed with. Still surprises me that this is my first truck with over 200k miles and also my first truck that doesnt have a constant glowing CEL

 

It should do this anyway. That is normal.

 

Did you check the coolant system for air?

 

https://www.youtube.com/watch?v=G2NGAHjPbNU

 

Okay changed the thermostat, theres no air in the system. Still have the same problem. Still takes a while to warm up and temp gauge still drops when accelerating and when parked (sometimes).