My 98 Accord Vtech engine has been having a temp gage fluctuating problem for over six months. When the car is first started from cold, the temp gage seems to work normally i.e. it starts to register after about three minutes of starting the engine. Temp rises to the normal 50% setting (gage pointer position) and may or may not stay there. As time passes say five to eight minutes, the gage pointer will either drop to zero or go to full hot or bounce between the two, slapping the top of the dash board with a medium tap (old pilot trick) the gage will go back to its normal position and for the most part remain OK for the rest of the drive.
What's been changed..
1) Changed the temp sensor (first with one from Autozone and a second one from Honda parts direct)
2) Changed the thermostat with one from Autozone (cooling fans seem to operate normally)
3) Changed the temp gage with new from Honda parts direct.
Still have the same problem. However, after changed the temp gage but still having the Autozone temp sensor installed, the system operated for about 30 to 45 days very normally with no fluctuation. But after that time it's back to the same fluctuating condition. Changing to the Honda sensor has made no difference.
Questions:
1. Is it possible that the Autozone temp sensor caused the replaced temp gage to fail? (Just seems like a poor grounding problem either internal to the gage or external in the wireing)
2. Is there any external wire ground for either the sensor or the gage? Note; the sensor wire, (one strand) was cleaned and checked when sensor was replaced all seemed OK.
3. Would air in the system cause this type of action? Note; no work was done on the engine before this condition first occurred and there is no leakage of water fluid nor is the engine actually running hot. Cabin A/C and heating operations are normal.

Sorry for being long winded but wanted to get as much details into this so a solid response can be had..

Thanks.

 

Wow...so that is interesting. Have you tried grounding the wire to your sending unit and checking for how the guage behaves? If I have it correct, if you ground the signal wire on the sender, the guage should read full hot. Watch for any fluctuations of the guage with the wire grounded. Another thing to check is coolant level. Make sure you are full up.

 

NO...do not leave the wire grounded/gauge pegged for more than a few seconds - Damage to the gauge will be done.

To me, sounds like a bad wire to the sending unit.....grounds and the gauge goes full hot, no connection gauge goes cold. You've replaced the "ends" of the circuit, time to look at the connection between the "ends".

 

Thanks Jollyhonda. I have tested the gage by externally grounding the wire off the temp sender. The gage goes hot when grounded to the engine block and cold when ground is removed. Thanks also to poorman212, too for the comment about leaving the gage grounded to long. I had read up on how to test the gage grounding before I tested it the first time. Also, I have with the use of a volt meter rung the wire from the send unit to the wire plug at the instrument cluster and it seems to be OK i.e. have continuity (static condition) but might be shorting with the engine running an the car moving. Fluids within the radiator are topped up.
Again, thank you both for your comments.

 

Well the problem is solved or better said, I know the "where and what" is causing the fluctuation. Its either a bad socket, or a bad crimp on the gage wire harness, or the motherboard has a crack.. With the ignition switch on and the instrument panel trim removed, I can wiggle the plug wire (with a long screwdriver) that plugs into the motherboard (right side) and cause the temp gage to fluctuate. Located the actual wire within the plug and it appears to be tight within its pin socket and the male pin within the plug receptacle (on the motherboard) appears OK. Problem now is do I really want to take the motherboard out and look for a crack?? By the way, Honda no longer sells the motherboard. I'm thinking to try and find a total instrument panel from a junkyard and try that. Problem there is the odometer reading will have to be reset by Honda and they will probably charge more for that then if I just bought a totally new instrument panel direct from them and had them install it. Oh well, life goes on in the fast lane..

 

Well it's fixed and all is well. I found a company that sells instrument clusters and for a few dollars will set the odometer to match the current car's original values, and seal the odometer with certified seals... I replaced my complete cluster and have been operational problem free since the end of May 2017. The company if anyone needs it is;

Tanin Auto Electronix Speedometer Repair, Odometer Correction ...

https://www.taninautoelectronix.com/

Tanin Auto Electronix is your source for automotive instrument cluster repair, instrument customization, LED design, odometer correction, and DIY automotive

They are located at; 7012 Hwy 31, Ste 100 Racine, WI 53402 and provided me with great Customer service and very prompt action.