Dash engine heat gauge

So you need to consider changing the temperature sending unit.

Looks like this http://www.rockauto.com/catalog/moreinfo.php?pk=1393291

I changed both sending units computer 2 wires and engine engine unit 1 wire. Still have problem.

Ok, so it sounds like a sticking thermostat. The engine keeps getting hotter until the thermostat finally opens up and then the rest of the day it works. I used to have that in the motorhome when I just ran it once a week in place. I'd keep staring at the temperature gauge while it got closer to the Hot, then the thermostat would finally open.

Changed thermostat twice. I do not think the engine is over heating,just a bad reading .. but why? How can I check temperture,with out depending on gauge?

I have no idea. I have a laser thermometer that I've only used to shoot the front and back of catalytic converters. I imagine if I had the same problem I could shoot the radiator, heads, freeze plugs.....

Sending unit varies resistance to ground as temp changes. If you know your not overheating then I would assume that the wire is shorting to ground somewhere giving you the max reading. Inspect the wire especially arround the manifold/header area and repair if required.

That sounds like a area to look at.....will give it a try. Thanks