Temp Gauge problem MU 2.6 4ze1

[VaJJs]

Hey i wasnt sure if i should put this in electrical or engine. anyway ive finished uni for the year and have time to work on my MU
ive had it for almost a year and the temp gauge has never really worked i had a look at it at the start of the year but was stumped so im hoping i can get it solved this time with the great members of club isuzu.

Problem: the problem is the temperature gauge always shows cold, when you start the car it comes up that fraction to show its got power but after driving for hours it will never raise more than a mm, it barely registers on the gauge

What ive tried: i replaced the sender (located under the intake, got to it through the wheel well) i guess its a possibility that the brand new one was a dud???
i have also tried the grounding the guage wire and seeing if the gauge pegged and it did, so does that mean the gauge is good?

the MU runs great (other than using a fair bit of fuel $15-20 per hundred kms) and cooling system seems to heat and pressurize, so all i can think is either maybe the sender is bad, the gauge is bad, the coolant isnt flowing past the sender or the temperature just isnt getting high enough.
so if anyone could post some testing instructions or point me to the right place ill try it all even retry the tests ive done, ive done alot of reading and cant quite figure it out. thanks.

[geeves]

is the termostat ok?

[VaJJs]

that came up sometime before and i eliminated that as a possibility cant rmember why, ill pull it out and test it tomorrow, will feel like a bit of a fool if it is that. thanks.

[VaJJs]

ok so i checked the thermostat today and it did seem like it was dodgey, it had holes drilled around the flat area so anyway changed it put in the new one and still no change, gauge stays at the bottom throughout a 400km trip, car is definitely getting heated but i dont know if it is high enough to register on the gauge? any other suggestions or procedures to try?

[pig75]

My 2.6 sits @ 1/4 on the gauge.
Was the thermostat a 82deg?
When the vehicle has been sitting over night and you start it up can you see water moving around the radiator by looking where the cap goes on? If so the thermostat is not working.
Was the sender for a 1990 2.6 rodeo?
Did you bleed the thermostat after you replaced it?
Can you touch the radiator after a 5-10 km drive? if you can i would try covering the front of the radiator with cardboard and going for a drive and put the heater on to see if the gauge comes up. And keep seeing if you can touch the radiator

[VaJJs]

yeah id be happy if it sat on a 1/4 but yeah it doesnt quite make it even to the start of the bottom of the line on the gauge.
the thermostat had an air bleed hole thing which went to the top of the housing and car was on an incline up, topped up the radiator an after the drive yesterday the radiator was quite hot, hard to keep your hand on it for a few seconds.
today started it and watched the water in the cap and it wasnt moving, pulled out the sending unit again cleaned any gunk off it put it back also put a new connector on the gauge wire and tested it again with groundin and gauge pegged, took it for a drive around town and gauge still didnt rise. ill replace the sending unit again on the off chance i got a dud or they gave me the wrong part and let you know the result.



UPDATE: changed the sender unit and still no change, car is definitely getting up to heat, also tried with a bit of cardboard infront the radiator and it made it hot quickly. have just found the heater does not work, air comes out normal temp when set to hot, heater appears to be hooked up but i maybe be looking at the aircon. will the heater stop the temp reading?
oh also yes the thermostat is set at 82 degrees and yeah the sender was for a 2.6 4ze1 rodeo, none of the places even had the isuzu mu listed for temp sender

[slightlydodgy]

Almost sounds like the water isnt circulating past the sender unit (?) maybe theres a blockage somewhere