Today I was heading over to a town 15 miles away to attend an auction. I noticed right before I got there that my temperature gauge was near H, but not in the red yet. Normally I run right in the middle all the time. So I figure my thermostat must be stuck shut. We pull into a parking spot and I popped the hood and let it sit. The reservoir tank started spilling over. I think this is in part because I replaced a coolant hose last month (lower radiator to water pump) and I probably overfilled the reservoir a bit. Anyway, it was obviously HOT. Every hose in the system was hot, and pressurized (top hose, bottom hose, heater core hoses, throttle body hoses…)

So I sat at this auction and let the truck cool down completely and I tapped on the water neck with a tire iron hoping I'd bump the thermostat into working. We left for home on a 55mph highway and I got about 10 miles when everything was back up to hot. I pulled over before it could go into the red. It wasn't noticeably high in the reservoir this time, but I was too scared to continue on. I called a buddy to come get me and then I went back with my car and my tools. I removed the water neck and pulled the thermostat out. I figured I'd drive home without the thermostat. So I yanked it and then refilled my radiator with coolant (I had a jug in the bed) So I started the truck and I heard the liquid rushing through the heater core, which is great.. (water pump is not making any weird noises or anything, and seems to be working) I'm about 10 miles down the road again and we're back at HOT. This makes no sense to me. So I waited for the truck to cool completely again and I popped off the radiator cap. I squeezed on every coolant hose to make sure I was able to get the coolant to bubble up (I was trying to figure out if I had a plug somewhere in the system.) Squeezing each and every hose produced a result at the filler neck of the radiator.

So I figured I was going to just drive her home. I made it home just as it was getting back to Hot again. So I just let it idle to see if it'd go into the red, and it never did. I have no thermostat in there, so I have no idea how the heck it's heating up so badly. One thing I did notice is that touching the radiator when it's hot and pressurized, the fins are cool to the touch, but the hoses going in the top and bottom are hot and pressurized. I figured since I was able to gurgle out the fill neck by squeezing either, that my radiator was not plugged up though.

I'm looking for help on what to trace. Should I just buy a new temperature sensor? I bought a fail safe thermostat (when it burns up, it fails in an open position) I'm paranoid that I'll destroy my engine, so I'm trying to figure out what could cause this sort of situation? I figured even if the heater core or throttle body were plugged up, that the truck could still cool right?

What would you guys do? I couldn't tell if it was truly getting really hot or not. 120 degrees feels the same to my hand as 212 (ie: burns and hurts)

What kind of tests can I do to tell if it's a failed temp sensor, or if I have a backup somewhere? My coolant is kind of gunky (not horrible, but it needs changed out) Is there a possibility that the radiator is all gunked up and i'm not getting enough coolant through the passages to cool it, yet it is still able to go in the top and bottom??

Is there an electrical test I can do on the temp sensor? Will the temp sensor throw a code to the OBD if it fails? Thanks for any help.

-Luke

 

Luke, do you have a spring in that lower hose? If not then when the engine is running down the road the lower hose can be sucked closed and coolant will not flow leading to overheating. Last few years when I bought a lower hose they don't come with springs in them and I had to take the spring out of the old hose and put it in the new one. Let us know, Bill

 

Almost sounds like the radaitor is plugged up, since you say you hear coolant moving in the heater hoses There are bypass hoses around the thermostat which will allow some flow in block. Also you probably got all the air out of the system if you had it running for a month after the lower hose replacement, but it is real easy to leave a pocket of air in the system any time it is apart. You can try taking the upper and lower hoses off the radiator and back flushing the radiator with a garden hose to see what comes out and how much flow is thru the radiator- the lower hose should be the pump suction side. One other thought - if your old lower hose had a coiled spring in it; was it in the new one? Some hoses had a spring to support the hose while running to prevent collapse under suction. Another way is to take it to a radiator shop for a flow test. Good luck.

 

now that you mention it, there is no spring in the new hose.

however, when I had it idling in my driveway, it was still running hot and that lower hose was open (it was actually pressurized to the point I couldn't squeeze it) Typically once the flood gates open (the thermostat) things cool off immediately. Also, if there was a flow problem in the radiator, you'd think THAT might cause the lower hose to collapse right?

The old hose did indeed have a spring. I might have to dig through my garage trash, but I might have thrown it away (I think I did)

It kind of sucks.. Yesterday it was 74 degrees in Iowa, and today the high is 35, and we've already reached that.. COLD and windy today.. And I need to use my pickup later.. I think the cold should keep her cool enough to get across town and back though.

What I need to do is find one of those infrared thermometers and zap the block by the sensor to see if it's really as hot as it claims to be.

Where can I get a new spring for the hose if I don't find mine?

 

get a manual i forget what the voltage should be at temp sensor when warm the book says also tells you what it should ohm out to. dave

 

Gauge should require sender to send 74 ohms for a cold reading and 9 - 10 ohms for full hot reading.

 

Here's another part to my question:

Is it possible for there to be flow through from the bottom to top of the radiator, but the have the radiator passages plugged up between there? ie: is it possible for the coolant to circulate, but never get cooled if you have gunk in there?

 

It would be hard to have useful flow (Cross flow radiators or vertical flow radiators) with the core plugged - you could have a visible flow parked without enough to cool the engine while driving. The answer is yes to your question. Look at the number of individual tubes that run from one side of the radiator to the other and figure the percent of all -100% against say a 1/4 which would give flow but not proper cooling. Also what you are seeing at the top of the radiator is the output pressure side of the punp which is moving into the tank from the upper hose and is more noticeable. Keep working you'll get it.

 

A buddy suggested that I should just change out the water pump, but mine isn't leaking, and I did hear noise in the heater core when I had the air in the system yesterday.

speaking of which, since I put about a quart of water in yesterday when it was 70 degrees out, i'm paranoid that with the 16 degree overnight temp tonight I could have trouble.. I'm probably going to call in sick tomorrow and buy a water pump, temp sensor and just drain and fill the badboy.

I'm still scratching my head though.. I haven't checked the timing, but would a super lean condition heat up the block beyond what full flow coolant could keep at bay?

This all happened overnight though, so i'm thinking the radiator probably isn't plugged up... Either way, it's definitely time to start wrenching again.

Is there a way to verify the water pump is working correctly? It's not leaking, making any noises, etc...

 

The very first and only thing you should do is put the spring back in the lower radiator hose. Next would be to check the water pump impeller is on solidly, not loose on the shaft and not erroded.

 

luke, where in iowa are you at?

 

I'm up in Ames.

- - -

Yeah, I need to get the spring back in there. I threw away my old hose though, so I'm SOL for the time being. Tonight I drove 15 miles on the highway at 65 mph, and it didn't ever get hot, so I think my hose (at least at the moment) is not sucking shut.

Here's the problem revisited: Tonight when I got home from work I took the truck to the auto parts store to stock up on things I needed, and some replacement parts I might use for this job. I bought a new TPS, water pump, and temp sensor.

Anyway, we got into a bit of confusion at the store. Does my '94 302 have TWO temperature sensors? There is one on a water neck at the intake manifold, but is there another one on the block? Also, if there are two, which one sends the signal to the gauge versus the computer?

It's 50 degrees colder here today than it was yesterday (god bless Iowa) so I figured I'd go drive the truck around until it reached maximum temp on the gauge. This is what I got it up to:


This is just a bit above where it USE to read when I had a thermostat installed when everything was kosher.

I'm starting to wonder if the temp sender isn't overstating the actual temperature, because I was getting next to no heat out of the heater core. I was able to hold onto the upper and lower radiator hoses without screaming "son-of-a-b@#$!" which is what I'd expect since I have no thermostat in there. However, my gauge is telling me I'm at normal operating temperature.

The upper radiator hose and the engine-side heater core hoses were hotter than the other two, to the point it wasn't comfy to hold onto it bare handed, but i COULD. So what I'm getting as is that it almost seems like the sender has gone bad.

I don't know anyone who has an infrared thermometer, otherwise I would just go that route to verify the temp sensor is broken.

Opinions?

 

with out a thermostat it would stay cooler than normal so you wouldnt burn yourself

 

If you have a hobby shop near you, you can buy an infared temp gun. They use them mostly for r/c cars and are remarkably accurate and fairly cheap. The guns will read up to 350+ degrees F. Just a thought.......

 

Yeppers... but my temp gauge on my dash is reading right above normal, so I think something is funky.. I either have a plugup somewhere, or the temp sender is bad.