faulty water temp gaug: will not reflect overheating. Any ideas??

dixiemudtoy · 12-21-10, 08:32 PM

Hey guys...

I have a faulty water temp gauge in my '86 pickup. It reads cold when cold, and slowly comes up to normal operating temperature as it should, but it will not reflect overheating.

I have installed an electric fan and pulled the thermostat probe after the truck warmed up (to induce overheating), with a multimeter temp probe in the top radiator hose and clamped it off.

Both sending units (the one on the thermostat housing AND the one closer to the firewall, on the intake manifold I believe) have been replaced with new Toyota units. Also have been thru three or four gauge clusters to try out new gauges.

I figure normal operating temp is around 195 degrees, too hot is anything above 245-250. I let the truck get to 239 degrees, and the temp still showed low side of dead even on the gauge; this is obviously not reflecting accurately.

Is there ANYTHING left I can try or do to correct this issue, or will I just have to suck it up and get a gawdy aftermarket water temp gauge?

Any help would be greatly appreciated.

toy4xfun · 12-22-10, 05:01 AM

i run an auto meter temp and oil pressure gauge, if you are sure it is not the sending unit, then i would go with an aftermarket gauge, they are not just for looks, they are accurate, and will help keep you from doing major damage to your engine.

here is where i put mine...

that steering wheel is gone, i have the stock Toyota wheel back in now, the adapters on those grants are junk.

KLF · 12-22-10, 08:19 AM

Even at their best, the factory gauges are unreliable and very inaccurate. I also suggest something from Autometer, mechanical is better than electrical.

toy4xfun · 12-22-10, 08:25 AM

my oil pressure is mechanical, at the time i bought them the store only had electrical for the water temp gauge. but agreed that mechanical is the way to go.

dixiemudtoy · 12-22-10, 09:20 AM

Quote:

Originally Posted by toy4xfun

my oil pressure is mechanical, at the time i bought them the store only had electrical for the water temp gauge. but agreed that mechanical is the way to go.

Yeah, I've never had a problem with the oil pressure gauge; it has always appeared to be accurate. but those damn water temp gauges just never seem to work...the only thing I can think of is maybe the wire?? or possibly the cluster housing, maybe the paper circuit board is bad? But I have been told those never go bad.

I would really like to avoid going aftermarket...no offense, just not too fond of the look of external gauge duplicates of ones already in the bezel.

If ANYbody knows anything....please let me know...

toy4xfun · 12-22-10, 09:38 AM

did you replace this sending unit....

dixiemudtoy · 12-22-10, 02:12 PM

Quote:

Originally Posted by toy4xfun

did you replace this sending unit....

Thats the one where if you were to look about 6-8 inches behind the therostat housing, it would be sitting buried underneath all the vacuum lines between the plenum and the valve cover...right? if so, then yes I did lol

toy4xfun · 12-22-10, 02:18 PM

that is the one, if you replaced it and your gauge is still not working right, it would point to your gauge, i do not know of anyone that works on factory clusters, you could google it, you might find some one.

another option could be to build a custom gauge cluster using aftermarket gauges.

Chop Shop · 12-23-10, 10:25 AM

are you sure the engine is hot/overheating?

If you have a bad head gasket or a crack somewhere it will pump the cooling system full of pressure before the engine makes any heat and it will seem like its overheating.

Get it to over heat again and use your HANDS to feel the radiator all over and make sure its so hot you cant touch it. If you can lay your hand on it or its still cool then you have a different problem.

You could always put an aftermarket gauge in there temporary to see if it reads different.

dixiemudtoy · 12-24-10, 11:11 PM

Quote:

Originally Posted by Chop Shop

are you sure the engine is hot/overheating?

If you have a bad head gasket or a crack somewhere it will pump the cooling system full of pressure before the engine makes any heat and it will seem like its overheating.

Get it to over heat again and use your HANDS to feel the radiator all over and make sure its so hot you cant touch it. If you can lay your hand on it or its still cool then you have a different problem.

You could always put an aftermarket gauge in there temporary to see if it reads different.

Yes, the last time I tested it with the multimeter, it read almost 240 degrees, and the radiator was indeed too hot to touch. I purchased one last cluster, and if this doesn't solve the issues, then I'm done trying...it will have to go aftermarket I'm afraid.

Dingman · 12-27-10, 06:12 AM

Yes, those pesky temp sensors... I also had to install a mechanical, it works much better. Location suks, but on my trail rig, I'm not too picky.