My temp gauge stopped working and I don't know what is going on. I replaced the radiator, thermostat and temp sensor. When the engine is on and idling the upper radiator hose is tough to pinch because it is full of pressure and then when I rev up the engine the hose loses pressure (probably because the thermostat is opening).

The upper radiator hose is NOT hot but the heater core hoses are hot and so is the small hose going from the water pump to the thermostat housing.

So my question is, is there a fuse for the temp sensor? Can the sensor in the dash actually go out? How can I tell if the water pump is working properly?

Thanks!

 

Ok a follow up (by the way no responses?? man oh man whats goin on?) I took the truck for a test drive this evening. After about 10 minutes of driving I noticed the truck throttle becoming more and more sluggish almost to a point of stalling at a light. I pulled into a gas station and stalled out. I tried to start it again and got a VERY sluggish turn over too slow to actually start. So knowing I have a temp problem I opened the hood (no leaks in the radiator or anything) but the overflow was bubbling. The upper radiator hose was hot and under amazing pressure. I couldn't even put a dimple in it by pinching it. I used a VERY thick towel and readied myself for a small explosion and twisted off the radiator cap (wich was cold by the way) and as I expected an utter explosion of radiator fluid and water. After 30 seconds the water stopped coming out and the pressure was released from the upper radiator hose.

I refilled the radiator with cool (not cold) water and doused the engine block a little (not too much for fear of cracking it). The truck started fine after that. I assuming the heat is expanding the metal somehow causing the engine to work harder. And once it cools off again it can run again. I KNOW I KNOW this is a SERIOUS problem so I have grounded the truck.

Can this problem be as simple as a radiator cap? Why don't I have a temp reading? I was reading if the temp gauge isn't working then you shouldn't drive the truck because the computer doesn't know how hot it is...is this true? HELP HELP! and thanks!

 

first off, hook a mechanical guage to your system, stock gauges are worthless. drive it with a carful eye on the gauge and if it hits 220 or so (or 230, not shure) pull over and let it cool. First off i am not shure that the engine uses the temp sensor besides on warmup to understand the engines cold. but still just to be safe i would get a T fitting and hook both sending units to the intake. but as for the heating, i dont know, my broncs 351 holds the upper radiator hose under highpress anyways( icant skeeze mine eather) if your truck is over heating really fast, i would replace the thermastat. but thats my best guess

 

Thanks for the reply. The thermostat is BRAND new I bought one that will fail in the open position IF it fails. But it is brand new. And when the engine is cool and I start it the pressur in the upper hose is tight and when I throttle the engine it drops a little as if the therm opens and coolant is flowing.

 

Definetly go with a mechanical gauge! can't beat them.
See what the temp reads while driving, my 302 never goes beyond 210 unless I am ideling with the AC on in the summer then it sits at 225 or so. Does the whole radiator feel hot or cool, run your hand down it to find out, Maybe a partally blocked radiator??(just guessing) My upper hose on my 302 does not get hard until it has warmed up completly(195-210). Did you or somone else put the thermostat in?? Again I am just guessing here but maybe it is in backwards??? What year and size engine is it?? If it is close to mine I can look in up in the Haynes manual and see if they have anything listed in their troubleshooing section. It would appear that coolant is flowing through the thremostat all the time in order for pressure in the upper hose(I could be wrong) lets assume it does. When you rev up the pressure goes down, do water pumps have any sorta of bypass valve in them, say the water CAN'T flow(assuming COMPLETELY blocked) so the pump will bypass it???? I am thinking maybe when you rev up and the water won't flow so it bypasses it...(hence the drop in pressure in your hose). Well I am thinking outloud here, I really don't know enough about it so I am just guessing. I would check the radiator when hot and see if the whole thing is hot(no cool spots) Maybe it is clogged somewhere. but yet you have pressure in the hose and when revving up the pressure goes down. I will keep thinking

 

hhhhmmm sory man, my best guess is maybe there is somthing wrong with that thermastat. sry thats my 2 cents.

 

Will the entire radiator be hot when the truck is hot?

 

I belive it should be, after the truck is at normal operating temp, but it might not be if somthing else is wrong somewhere else. Just somthing to look at. Since it is new I would not think it to be clogged already. Maybe you could get a backflush kit and backflush your cooling system.
I agree with jojo,
I was thinking either the thermostat is just plain bad or is in backwards just a guess though.

I reread my first post and boy do I sound stupid That's what I get for thinking outloud

 

Yes...the entire radiator should be hot when warmed up...unless 1 of 2 things have happened...1 - You are seriously low on fluid in which case the lower half will be hot only....or 2 - you have a clogged radiator and the fluid is flowing only through part of it. Good luck! (And check the thermostat again...just to be sure that it isnt in backwards.) You said you got the type that fails in the open position...maybe when you rev the engine, it thinks it failed and opens..that why you are getting loss of pressure in the hose.

 

I would look at the thermostat also due to your statement about the bypass hose being hot but not the upper hose. When you start it up the upper hose should be cold but, as soon as ther opens you should feel the hose heat up.

 

heybrent,
Did you ever get your problem figured out?? I was curious to know what the problem was.
Thanks,
Kevin

 

Haven't figured it out yet. I am thinking I need to replace the radiator. The thermostat is in right and I had to use some of that aluminum radiator stop leak a few times to get the radiator to stop leaking. Pehaps that clogged it up completely. It was a used radiator anyway.

 

I guess it could be a clogged Radiator, did you try to feel it and see if it is warm throughout the whole radiator?? That might help you find a cool spot(blockage). I have never used any of the radiator stop leak products but I have heard nothing but BAD things about them. Hope you get it fixed.