Gauges Rising Simultaneously?

[crowmeyocks]

I have a Bantam short bus (basically a ‘91 E350) that I got at auction a year ago. Worked thru tons of problems but with it warming up this old glitch is starting to worry me. First off forgive my noobness, not only am I a mechanic-by-necessity, I’m a total dope when it comes to electronics. I just don’t get it and they even act weird around me ha. So layman terms would be appreciated here.

So here’s the issue: since I got this rig the factory gauges have been (of course) nonsensical and worrying. Although my temp gauge tended to ride in the middle most times, I noticed it would tell me I’m overheating going up hill sometimes, so I’d pull off and wait for it to drop (no rule there—often at idle is when it climbs into the red and I get mixed results with giving it gas, turning it off, and waiting it out—engine temp light never has come on by the way, only flashes when starting). Anyhow I thought I had a coolant system issue until I noticed that my oil pressure AND gas gauge would also climb whenever the temp gauge did. So against my better judgement I tried to see what would happen if I just waited it out, an lo and behold I never have seen signs of actual overheating and the gauges level out all together after a bit. It runs totally level without a hiccup as far as I can tell no matter what my readings.

Lately the temp gauge has been riding around the M or A on regular highway drives tho, and I’m generally getting the sense that my paranoia is going to fail me some day when I need it most.

So what do all these gauges have in common that would cause them to rise all at once?

Before I go doing a coolant flush and a thermostat job and buying a bunch of sensors aftermarket or stock I’d like to know what the common denominator is here so I can attempt to get at least mildly sensible readings without dropping a mint on an aftermarket set up (which I know is the best solution, but I just really can’t afford to do coolant system work AND a dash overhaul at the moment).

General coolant system and dash sensor troubleshooting links / rules of thumb (especially for thermostat operation) would be much appreciated.

Truly forgive my ignorance, this is my first diesel and I’m just learning as I go. It’s also kind of my life line. If it breaks down I’m dead in the water. Any help is appreciated!

 

[lkrasner]

Following. My 94 short bus does something similar.. Any changes in the electrical system (glow plugs cycling, headlights, turn signals, etc) all make the guages move. My fuel Guage seems OK, but the temp and oil pressure definitely respond to battery voltage somehow. I'm guessing a bad ground and / or some coroaded wires are to blame. Haven't really looked into it yet.

 

[IDIBRONCO]

It could be a ground issue like Ikrasner said. I don't know about Brick nose and OBS style trucks, but some of the older ones had a voltage regulator behind the instrument cluster. When they got older, they would do this. From my personal experience, the engine temp and oil pressure gauges would both read higher or lower together. These factory gauges aren't much better than an idiot light. Their main job is to make you feel safe about your engine. A good set of aftermarket gauges (either electric or mechanical) is the way to go. Now don't get rattled when you install an aftermarket oil pressure gauge and the oil pressure seems REALLY low. IIRC, the minimum spec is 10 PSI at a hot idle. The general rule of thumb is 10 PSI for every 1000 RPMs. 20 PSI at 2000, etc. Here's something else to consider, if your oil pressure and temp gauges rise and fall together, your engine temp will rise with less oil pressure, not more.

 

[YJMike92]

You might check the charging voltage when the problem is happening. If you are overcharging it could cause the gauges to read higher.

 

[snicklas]

I’m with @IDIBRONCO on this one. The IVR (Instrument Voltage Regulator) on the back of the cluster. The gauges through the 86 Model Year F-Series trucks and through the 91 Model Year E-Series vans have the older design concept gauges that are 6 volts gauges. The IVR is a 50% duty cycle switch. It switches on and off, to provide the equivalent of 6 volts to the gauges (the gauges don’t react quickly to the voltage change, which is why the stay where they are when the relay is off and not sending current to the cluster). So when everything is working properly, and the IVR is switching (same idea as the afterglow on the 7.3 style controller, switch on and off to keep the plugs hot without burning them out. Or riding a skateboard, periodic pushing with your foot keeps you moving, power on, off, on, off......) the gauges read where they should. If the IVR sticks on, then the gauges (temperature, oil pressure, fuel, battery) will show higher than they should. This is why it seems like it’s overheating when it’s not. I’ve had this happen on both our 83 F-150 and 85 E-150, and the first couple of times it will freak you out. After it happened again, I noticed all the gauges were high, and I happened to hit a bump and they all settled back to where they should be. The next time it happened, I gently thumped the top of the dash, and they all settled again.

When they changed the body style in 87 on the trucks and 92 with the vans, they went away from the IVR setup, and the gauges didn’t do this anymore.

 

[crowmeyocks]

Thanks for the responses all. The IVR sounds like the likely culprit, I’ll tear into the dash and see if if I can clean it up or replace it son and report back. Will also try to bang on the dash, possibly with my head if all else fails ha.

I took a look at my temp sensor just for kicks and it was definitely wicked hot to the touch after pulling uphill for a couple miles, but the radiator and thermostat seem fine if the hose temps tell me anything.

 

[crowmeyocks]

Just for the books, I found this from another forum:

“One thing that can make your gauges move up and down is a bad ground between the engine block and frame. You instruments are grounded at the dash panel to the body. The sending units are grounded to the engine block. If you have a bad or dirty ground between the block and frame, or between the frame and body, there will be a voltage drop across that bad ground, and this will make your gauges change.”

I should clean up my grounds anyway, I never really have, and the glow plug bypass I just installed seems to be losing about a volt between the hot side of the controller and the opposite post that sends to GPs. I have it grounded to the uh, um, thick metal thing between the the steering column and the fuse box. Again, will report back. Cheers!

 

[lkrasner]

Just for the books, I found this from another forum:

“One thing that can make your gauges move up and down is a bad ground between the engine block and frame. You instruments are grounded at the dash panel to the body. The sending units are grounded to the engine block. If you have a bad or dirty ground between the block and frame, or between the frame and body, there will be a voltage drop across that bad ground, and this will make your gauges change.”

I should clean up my grounds anyway, I never really have, and the glow plug bypass I just installed seems to be losing about a volt between the hot side of the controller and the opposite post that sends to GPs. I have it grounded to the uh, um, thick metal thing between the the steering column and the fuse box. Again, will report back. Cheers!

My grounds, and basically every wire in the thing are a hot mess. in fact, I can think of 2 ground straps I've noticed completely broken. Stupid thing needs way more electrical work than I'm willing to put in. Fought glow plugs for weeks only to find their main power wire was corroded beyond being able to carry any current.