88 FJ62 - Coolant temp cycling (1 Viewer)

[billiam]

Up until the last week the coolant temp has been rock solid at the first line. Now it will cycle up into the red and then come back down, the cycle taking no more than about a minute or two. Doesn't seem to be consistent with engine load but have only noticed it at freeway speeds. Is my thermostat going bad or ??

 

[YooperCruiser]

Yeah that sounds like the thermostat

 

[Godwin]

Up until the last week the coolant temp has been rock solid at the first line. Now it will cycle up into the red and then come back down, the cycle taking no more than about a minute or two. Doesn't seem to be consistent with engine load but have only noticed it at freeway speeds. Is my thermostat going bad or ??

Thermostat and cooling system may be ok. Next time you notice the temp gauge spiking take a look at the fuel gauge, if it is also rising (and drops in concert with the temp gauge) then this is a minor electrical issue within the gauge cluster. Well known fluke of the 60 series.

 

[Prairie Swamp]

I wonder if @Spook50 has had time to work on his improved voltage regulator for the gages?

 

[OSS]

The problem is the temperature gauge

 

[Michael Hanson]

Hi, As stated temp. Gauge. Seems to be right after the fuel is filled up. Mike

 

[billiam]

I haven't noticed the fuel gauge moving around at the same time but not sure I was paying attention to it - spiking water temp had my attention. The times I've noticed this it does seem to be the first few trips after filling up. I'll keep an eye on it and try to dig into the thermostat as soon as i can.

 

[Spook50]

Up until the last week the coolant temp has been rock solid at the first line. Now it will cycle up into the red and then come back down, the cycle taking no more than about a minute or two. Doesn't seem to be consistent with engine load but have only noticed it at freeway speeds. Is my thermostat going bad or ??

What does your fuel gauge do when this happens? If it stays the same, there's a problem with the temp gauge itself. If it fluctuates as well, the problem is the regulator, which my project will fix once it eventually comes to fruition.

@Prairie Swamp very little progress this year unfortunately. Can't believe I started it 7 damn years ago and still haven't finalized it. The latest version didn't allow enough current to the gauges to raise the needles at all, so I had to find diodes that would allow more forward current to see if that'll correct the issue. I also saw the need to build a more legitimate test bed that would allow for more extensive testing so that I can actually bench test each regulator for quality control instead of having to install each one in my own truck and constantly taking the dash apart.

 

[billiam]

Got some freeway time in yesterday and saw both the fuel and temp gauge rise and fall together. The FAQ says it's a dirty ground and cleaning that will resolve the issue. @Spook50 - you mention that the problem is the regulator - does cleaning the ground fix this or does the regulator need to be replaced?

 

[Spook50]

Got some freeway time in yesterday and saw both the fuel and temp gauge rise and fall together. The FAQ says it's a dirty ground and cleaning that will resolve the issue. @Spook50 - you mention that the problem is the regulator - does cleaning the ground fix this or does the regulator need to be replaced?

99% of the time the issue comes from the contacts on the regulator, which is built into the fuel gauge. It's a mechanical regulator so operates by a pair of contacts opening and closing. Over time those contacts get buildup from arcing and start sticking together or not making contact when they're closed. The solid state regulator I'm working on bypasses the mechanical and eliminates the sticking and fluctuation of the needles. Later into the game I modified the design so it would be compatible with 24V trucks as well (which involved just finding the right combination of components to handle greater than 12V on the input). That's the point I'm trying to finalize now.