Hey guys,

Last night I noticed my cars temperature gauge reaching almost to the H. I noticed it has to do with my voltage. I sit at 13.8 v at idle and when i turn on my headlights I'm at 13.2-4 and 13.0 with fog lights on which seems normal. If my voltage reaches about 12.5 from using the Windows , radio , radiator fan turns on, etc the temp gauge will start rising... If I turn off the headlights and it pops back up to 13.4 volts because now the radiator fan is on.... The needle goes back to where it should be reading about halfway. I have an apexi turbo timer I'm getting the voltage readings from and I use a pc680 mini battery. What's going on?

Note: I have noticed that I sometimes I drop voltage randomly to like 12.5 volts for a few seconds intermittently when I turn on an accessory like the headlights and the idle drops for a few a seconds then it pops back up to 13 and slowly rises to 13.4 but it has always done this and never caused an issue before.

Edit: it does it with just the headlights on .... If it's at 13.4 volts with headlights on, once the cooling fan comes on it goes to 13 volts and the gauge rises once the cooling fan comes on.

It seems that regardless of which accessories are on once it falls to 13 volts or less the gauge rises...

 

Have you actually verified if you are overheating? It's one thing if this is just an electrical gremlin, but if you are actually getting too hot you gotta deal with that first.

 

Well I would normally verify that with the gauge that isn't working. How do I see otherwise? I touched the motor and it felt no hotter than before and when I turned the heat on the current draw made the gauge go higher instead of lower as it should.

 

Optimally I would suggest logging the ecu, as it uses a separate sensor from the cluster. You could probably do some observations, like if the fans are cycling on and off then you are probably staying within normal range. If they come on and never shut off though that would be a red flag. I would also advise checking that all chassis grounds are tight and not corroded. Next step would probably to take readings at the sensor itself to see if that has failed or if the issue is further up the pipe.

 

The fan is cycling on and off as it should. I should be checking the coolant temperature sensor correct ? I can plug in and log with ecu flash and post back. What are the optimal temperatures I should be running at ?

 

my 03 evo 8 with 85% bolt ons runs anywhere from 195 degrees to 203 degrees at WOT according to my evoscan logs. car has never had overheating issues. So you could use that as a reference.

 

also, I am no mastermind when it comes to electricity, but from what you are describing, I would check your alternator positive feed and the ground, corrosion or loose connections can definitely alter the output of the alternator. could also be a draw, since you said it only happens when you turn your headlights on, if that's the case, there is high resistance (most likely corrosion) somewhere in the circuit, I would have a reputable shop look at it. please keep us posted.

 

For what it is worth, there's a ground, intake manifold to firewall, that when disconnected or corroded, is said to screw up the temperature reading. The sensor itself is a variable resistor that has higher resistance when cold. So, it seems to me that adding the resistance of a bad ground would cause it to read colder. However, I remember reading the opposite on this forum.

 

Update: It runs at the same temps whether it's at 11v with everything going (blower, headlights, fog lights, cooling fan, window motor, etc) with the gauge on full Hot or if it's at 13.8 v with nothing on and the gauge in the middle. I just logged with evoscan. My readings varied from 195-206 and when the fan would turn on it would go back down to 195 to 198.

It's not isolated to giving false gauge readings with just one thing on like the lights. Regardless of what's on once it falls below 13v it will start to raise to H on the gauge. On Tuesday I will try to remove some things to get more access to the alternator to check connections.

One thing I just remembered from a week or two ago was I accidentally hit the upper part of an Uicp on the battery and it touched something (I want to say it was the radiator?) and zapped. Didn't really think anything of it. Could this have fried something?

 

I daily drive this car so I'd like to get this figured out asap so I know when the car is actually overheating. I guess I will remove my catch can and strut bar to gain access to the alternator to check connections. I did spill a bit of oil on it when I replaced the mivec line and filter but that was months ago. I'm curious if I may have damaged something when I accidentally touched the Uicp to the battery and I think the other end hit the radiator or radiator support or somewhere in that area and a few sparks went off. This was like 2 weeks ago. Where is the temp sensor for the cluster heat gauge located? Other suggestions?

 

this should help:

 

 

Thank you

 

Upon driving to work this morning I payed close attention to all of my readings. Something is going on with the charging system. It started off at 13.8v when I left and it was warmed up. After about 15 minutes it was down to 13.4 v with no accessories on and after about 20 more minutes It was down to 12.9-13v with no accessories on. Once the cooking fab kicked on it would drop to 12.5 or 12.6v. I checked the voltage at the battery after turning the car off and it was at 12.4v... Which is normal. I will have to get the alternator and battery tested and check the wiring. Since the motor only has had like 6000 miles out on it since the rebuild I doubt there is corrosion on the alternator... Maybe somethings loose.

 

Can the belt slip on an alternator without squealing? I also noticed at WOT it drops to a very low voltage like 11.5v or something.