bjafeman

I've been fooling around with my cooling system recently and am having an overheating problem. In the last 8 or 9 months I've replaced the water pump, thermostat, both radiator hoses, both coolant sensors and even the thermostat housing (overtightened one and broke the ears off).

Recently I changed the rear coolant sensor. After doing that I noticed that the truck started to overheat. As soon as the engine would get up to temp it would keep on climbing up the gauge and then eventually set off the CEL.

Thought it might be a busted thermostat, so I changed that out yesterday. But, after I buttoned everything up, had a few tacos - yesterday was cinco de mayo - refilled the coolant and test drove it, the overheating problem was still there.

As I'm doing my best to say in Spanish I start looking around the truck to see if I can find anything wrong. Some of my oxygen sensor wires had pulled out of the sensor. So, obviously this needs to be replaced.

Can a bad O2 sensor cause the engine to overheat?
Or, do I need to get ready to pull the pump...again?

91351

no on the o2 sensor, try a clutch fan

bjafeman

Any suggestions for testing the fan clutch?

I just spun it with the engine hot (but off). A decent flick made it turn a little less than half a revolution. It definitely didn't seem like it was pushing much air when it was running.

While I'm at it. Any good tests for ruling out a bad water pump as well?

91351

for the fan the i do it let it sit there and run a bit. look at the fan if its spinnin slow. (i stick my hand in it and if it stops its bad)it might hurt a little. you can do it that way prolly not safe but it works. for the water pump it normally leaks when its bad. do the fan thing a couple of times if you have to, to make sure. but thats the only thing you havent replaced

bjafeman

Cool test. Not gonna ask what happens when the clutch isn't bad. Maybe I'll use a magazine instead of my hand...Maybe the neighbor's kid wants to make a dollar? We'll see.

I'm pretty sure the water pump is still working - been on the lookout for the weep hole leak. I paid the extra $$ for OEM and I'm gonna be pissed if I have to replace it again. Agree that the clutch is the most likely culprit since it's the only thing left.

Thanks for the info.

91351

your hand justs bounces off unless you stick it all in on one whack

Just call me Sean

iTrader: (1)

Maybe your radiator is plugged. If the thermostat is open you can look inside the radiator and see the water being pumped. Maybe the head gasket is bad, pull the spark plugs and check for glycol deposits (powdery white) or one or two that are cleaner than the others. You can TEMPORARILY run without the thermostat installed and see if it makes a difference. If the engine is warm and the fan won't spin much with your hand (not running) then it's probably good.

bjafeman

I did the hand/fan test...not that bad actually. If you wear a glove and pay attention to which way the fan blades spin/face, you can do it without losing any fingers. Clutch acted the same no matter how hot the engine was, so I changed it to be safe (and it's the last piece of the cooling system I haven't changed).

I got a new fan clutch put in place and the truck isn't overheating anymore. But, it's still showing that it's real hot on the temperature gauge (pretty much always just before - or on - the "L") even though it's not that hot. Here's why I think the engine isn't as hot as the gauge is reading:

1) After a cold start the gauge shows the temp below the "N". As the engine warms the needle starts moving toward the L at a slow but steady pace. Maybe 3 minutes if it's just sitting still at idle. When it's doing this, the top tube of the radiator is cold. Once the needle gets to the "A" it stabilizes on or just past it. This is when the top tube of the radiator gets hot, I assume it's b/c of the thermostat opening.

2) Once the gauge gets to the L, it stays there. Whether it's a cold cloudy morning cruising a 5 mile downhill or 90* in the afternoon with the AC blasting and climbing back up the same hill, the gauge pretty much sticks to the L. I've repeatedly tested the truck in conditions that easily made it overheat when it had a bad water pump and even though the gauge is reading hot, it's acting normal.

3) All signs indicate the cooling system components are working fine (aside from the sign of them all being less than 7 months old). Radiator hoses get hot after a while, which indicates that coolant is flowing. Looking in to the radiator, you can see the coolant moving around when the thermostat opens. No bubbles in the radiator or coolant loss. Fluid is new, green and tastes fine.

So I'm thinking that the new coolant sensor I installed is giving the wrong reading.

Is there any harm in the sensor reading that the engine is running hotter than it really is?

I know a cold reading will make it run rich, but what about hot?

The reason I'm asking is b/c if the engine management is OK with the gauge showing hot, I'm just going to put a T into the block sensor and run a second temp gauge (with actual numbers) under the dash.

91351

that would work i guess, but im not sure if theres two temperature unit, one for temp gauge, one for computer, not real sure.

bjafeman

Yeah, there are 2. One front and rear. I know they both work together for the dash gauge signal. Not sure about whether or not the same is true for the computer.