Oil temp gauge issue

David Anderson · August 09, 2019, 11:02:05 AM

While I have my oil drained it would be a good time to address an issue I've had for a long time. My VDO oil temp gauge reads high. The gauge will show 240 and the IR gun shows about 210 at the oil pan where the sender is screwed into the pan. Another issue is when I turn on the bus lights for night driving the temp gauge will go up about 10~13 degrees now showing close to 260. It's always read high. The sender was supposed to match the gauge when installed many years ago. I wonder if a ground wire on the oil pan to the frame would help.
Any ideas??
David

richard5933 · August 09, 2019, 11:47:49 AM

Can you get a two-wire sending unit to match the gauge? One wire goes to the gauge, the other goes to a ground source. Those are used for installation in places where the block isn't grounded or where there is some other insulating situation going on.

There are a few two-wire sending units listed on the VDO site - the one you want is called a 'floating ground'.

If the ground is the issue, this should take care of it.

luvrbus · August 09, 2019, 12:21:21 PM

David on the junction box where the gauges are ( left upper side) they have resistance loops for the gauges on a Eagle add a couple of more loops

David Anderson · August 09, 2019, 02:28:35 PM

Quote from: luvrbus on August 09, 2019, 12:21:21 PM
David on the junction box where the gauges are ( left upper side) they have resistance loops for the gauges on a Eagle add a couple of more loops

I don't remember seeing any on my metro bus. I added this gauge after conversion. Power is from circuit 78 (accessory and run), sender wire is front to back, (sender to gauge), ground is black to the common grounds for all gauges. Sender ground is the oil pan threads. I suspect a grounding problem.

luvrbus · August 09, 2019, 03:20:55 PM

I forgot you were dealing with the Houston Metro Eagle but a resistance loop will work on any electrical gauge.I spent a lot of time making my Eagle gauges on the dash read with a manual gauge loop and unloop for a week before I got it right lol Norris taught me that trick

Iceni John · August 09, 2019, 04:29:41 PM

Make sure there's no PTFE tape or thick pipe dope where the sender threads into the oilpan. It has to make good electrical contact there, so just a very thin smear of goo is enough.

I have two Speedhut single-wire temperature senders in things that don't have good electrical grounds, so for both I use 1/8" FPT brass reducer bushings, one with a 6-32 thread tapped into it for a ring terminal for the ground wire, and the other has a male tongue connector soldered onto the bushing. Both give good grounds for the senders, and hopefully accurate readings for the gauges.

John

richard5933 · August 09, 2019, 05:42:35 PM

What about a grounding strap between one of the oil pan bolts and the block?

buswarrior · August 09, 2019, 06:27:49 PM

Quote from: richard5933 on August 09, 2019, 05:42:35 PM
What about a grounding strap between one of the oil pan bolts and the block?

Going that far, i'd go to a good chassis ground to be sure of it. If the block ground is getting sketchy, no change in results.

2 birds, one stone.

The problem is definitely grounds and/or induced currents. Headlight fluctuations is a give away.

Happy coaching!
Buswarrior

luvrbus · August 09, 2019, 08:26:27 PM

Eagles have a good grounding system it should have a ground cable from the frame stud to the engine from the factory just like on the starter

David Anderson · August 10, 2019, 11:27:48 AM

I ordered a new VDO 300 degree sender from Summit Racing, $27 with shipping. The old one had hairline cracks in the insulation. I ohmed out the drain pan to the frame and it went to zero, so the ground should be good. I will report back after I install the new sender and attempt a test drive.

David

David Anderson · August 13, 2019, 04:45:39 PM

Installed the sensor and took a drive. It stays around 200 until I turn the lights on then jumps to 230

I'll have to pull the dash and check some wires I guess.

richard5933 · August 13, 2019, 06:22:52 PM

Check to see if the gauge shares a ground with your light switch or the lights themselves. I've had a few that I needed to separate on different circuits to get them to play well together. Can't explain why, but my battery remote switches were acting screwy until I ran separate ground wires to each.

luvrbus · August 13, 2019, 06:40:48 PM

Run it through a relay David does it do it without the engine running and the lights on ?

David Anderson · August 13, 2019, 08:45:49 PM

Quote from: luvrbus on August 13, 2019, 06:40:48 PM
Run it through a relay David does it do it without the engine running and the lights on ?

Don't know, I've never checked it that way. I won't use the coach again for another week, so I may try a dedicated ground first. I do know that when I turn on my headlights, and or parking lights, my voltmeter on the dash drops 1 volt. It always has done that since I have owned the coach. However, none of my other gauges change with lights on or off. Only the oil temp.

luvrbus · August 13, 2019, 09:08:20 PM

VDO has a 800 number for tech support maybe save work by calling