LJ78 Fuel/Temp spike (1 Viewer)

[alecanglum]

Hello everyone!

Like millions of 2LTE owners before me, I have been spending my time chasing a random overheating issue on my LJ78. The temp will spike to nearly the red at random times with no consistency surrounding the driving conditions.

I’ve been assuming the worst, but today I noticed that the fuel gauge also spikes whenever the temp gauge goes. I was able to find a thread in the 60 series section about a similar issue that could be remedied with a voltage regulator, but couldn’t find anything pertaining to the 70 series.

Has anyone dealt with this issue before? Am I just thinking too hopefully?

 

[GTSSportCoupe]

Hello everyone!

Like millions of 2LTE owners before me, I have been spending my time chasing a random overheating issue on my LJ78. The temp will spike to nearly the red at random times with no consistency surrounding the driving conditions.

I’ve been assuming the worst, but today I noticed that the fuel gauge also spikes whenever the temp gauge goes. I was able to find a thread in the 60 series section about a similar issue that could be remedied with a voltage regulator, but couldn’t find anything pertaining to the 70 series.

Has anyone dealt with this issue before? Am I just thinking too hopefully?

If it was just the temp gauge spiking I would suggest there is air in your coolant. That is usually not a good sign, as could mean combustion gasses getting into the coolant. Can be simple like a leak or bad rad cap too tho.

However being a couple of your gauges have issues simultaneously, I'd agree the problem is more likely electrical. How long does this condition last? If you're able, use a voltmeter to check your alternator output. Or better yet, remove the alternator and have it tested/rebuilt as necessary. Also, check all the connections are clean at your alternator - I think if the plug connector is dirty it can cause problems like this. Check vehicle grounds, fuses, etc.

 

[coldtaco]

Check all the grounds you can find. Mine did that too when I got it and one day both gages started behaving themselves. I had been in the dash a few times and other places, probably having removed/installed different grounds during these times

 

[alecanglum]

If it was just the temp gauge spiking I would suggest there is air in your coolant. That is usually not a good sign, as could mean combustion gasses getting into the coolant. Can be simple like a leak or bad rad cap too tho.

However being a couple of your gauges have issues simultaneously, I'd agree the problem is more likely electrical. How long does this condition last? If you're able, use a voltmeter to check your alternator output. Or better yet, remove the alternator and have it tested/rebuilt as necessary. Also, check all the connections are clean at your alternator - I think if the plug connector is dirty it can cause problems like this. Check vehicle grounds, fuses, etc.

Thanks for the quick reply!

I have already been down the cracked head avenue. I tested for exhaust gasses in coolant and it showed negative. I also just replaced the radiator cap, because it seemed coolant was constantly overflowing from the tank. It would never boil, just slowly spill over. I believe this issue was solved by the new cap.

the condition usually last just a few seconds and varies in how high the gauges climb. I will start testing my alternator first. If that fails, I’ll start chasing grounds. Electrical makes my mind go numb, so this should be fun...

 

[alecanglum]

Check all the grounds you can find. Mine did that too when I got it and one day both gages started behaving themselves. I had been in the dash a few times and other places, probably having removed/installed different grounds during these times

Very likely that this is the culprit. All other gauges function normally, so it seems like that it could be a small, localized ground behind the cluster.

 

[Gun Runner 5]

Almost guaranteed to be a grounding issue. I’m fairly sure the temp and fuel gauge share a common power source.

 

[alecanglum]

If it was just the temp gauge spiking I would suggest there is air in your coolant. That is usually not a good sign, as could mean combustion gasses getting into the coolant. Can be simple like a leak or bad rad cap too tho.

However being a couple of your gauges have issues simultaneously, I'd agree the problem is more likely electrical. How long does this condition last? If you're able, use a voltmeter to check your alternator output. Or better yet, remove the alternator and have it tested/rebuilt as necessary. Also, check all the connections are clean at your alternator - I think if the plug connector is dirty it can cause problems like this. Check vehicle grounds, fuses, etc.

Well I had convinced myself that this was all electrical, but I’m currently sitting in a parking lot waiting for the damn thing to cool down.

Coolant is being pushed out the overflow again. Has a brand new radiator cap. Maybe the cap is bad or I got a false negative from the combination gas test.

 

[Pradita]

Hey @alecanglum, did you ever figure out the issue? Ignoring the fuel indicator blips, your problem sounds similar to what we're having with our LJ70 - posted in gory detail about it here: LJ70 Overheating Mystery: What have we missed? - https://forum.ih8mud.com/threads/lj70-overheating-mystery-what-have-we-missed.1258525/post-13959092