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faulty gauge???

scasey28

scasey28

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Guys,

So yesterday I took my k5 our for a drive up in the foothills. The outside temp was about 103. Here’s the problem, driving on city streets the temp gauge stays right in the middle. However when ever I go up hills and give it some gas, the temp gauge starts to climb to almost overheating. So as the temp gauge stated to peg in the red, I pulled over and used an inferred temperature gun and scanned the engine and radiator. The engine ranged around 180-190. The radiator was around 175. The hottest spot was near the oil pan, around 200. By these, the engine is running in normal range. So what do you guys think, bad gauge, faulty wiring??? Any thoughts would be great. Thanks.

-Scott
 
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My guess, and the probably the cheapest, is the sending unit and possibly the wiring to it is shorting out. The gauges rarely go bad like that. Try replacing the sending unit, about 5-10 dollars at your local parts store and go from there.

Josh
 
Josh,
thanks for the advice, I'll try changing the sending unit in a few days. Also when I change the unit is there any special measures that I need to do? Thanks

-Scott
 
Make sure the engine is cold, get yourself some plumbers tape to wrap the sender and the proper sized wrench. It should only take you about 5-10 minutes if that. Good luck.

Josh
 
Yesterday I replaced the temp sending unit and did a road test. Right away the h20 temp gauge makes it way into the red. So today, I went over and talked to my mechanic to get his opinion. He thinks that the fuel that is going into the carb could be getting to hot (fuel line that goes into the block is close to the headers) and should be wrapped with insulation. He also said to install a heat shield between the carb and intake. What do you guys think fuel problem??

-Scott
 
I'm really not seeing the connection between the fuel being hot and the engine guage being faulty. buy a cheap guage and test really simple to place in a temporary location and if you are careful you can prolly take it back when done if results are weird. ;)
 
I thought the same thing, however I figured that the gauge works correctly because it reads normal unit I drive the truck up in the hills Can I just unplug the wires from the stock gauge attach and reattach them on to the new gauge?
 
just disconnect at the sending unit and run a seperate wire to inside the cab, If I remember correctly there is just a hot, ground and sending unit wire. Depending on what year the vehicle in question is you would likely be better off leaving the dash guage and it's template/wiring alone until you zero in on it a little better.
 
Its a 72 blazer. I'll run down to autozone and pick up a cheap temp gauge try and hook it up. I'll let you know how it goes.
 
this thing is driving me crazy. Last night I swapped in a new temp gauge and did another road test. Even with the new gauge it says that it was over heating, yet the temp gun was only reading 190. Could this maybe be a water pump problem? Any help would be great. Thx
 
How old is the thermostat? Do you have the heater core bypassed?

You could have an air bubble trapped in the system (steam), and that is what the sending unit is reading.

I would take off the rad cap, and run it, watching inside the radiator for a large burp. If you see one, problem solved.

Make sure the heat control is on fully, so the entire system is circulating.
 
Also, if you are testing with a new guage, you need to use the sending unit that comes with it. The resistance was different between my stock one and the autometer I got. I tested it in the kitchen. :)
 
Do yourelf a big favor and buy a quality mechanical (Autometer gauge) and then you'll know for sure if you're actually having problems. You can keep the factory gauge in the dash and mount the Autometer gauge under the dash or where ever you want. Electric gauges aren't as accurate as mechanical.
 
What makes you so sure that your temperature gun is accurate? I'd boil some water on the stove and use that to prove that your gun is reasonably accurate.

What about a stuck thermostat? If the engine is hot, but the radiator is measuring "cool" maybe the coolant isn't really going anywhere....or at least not as efficiently as it should. What temperature t-stat are you currently running? Are you sure it's really opening at it's rated temperature? If you still have that pan of water boiling on the stove, you can use it again to check the t-stat for proper operation.

What about the radiator cap? Is it in good working order... if the truck is ACTUALLY overheating, the cap is only going to hold pressure for so long. Eventually it will blow open and let overheated water out. I don't have the ratings memorized, but the more PSI the cap is rated for, the higher above 212F you can run before it blows...

I think there might be something going on with an air pocket in the cooling system too (as was already mentioned). Let the engine run and get hot with the radiator cap off...make sure the t-stat is opening. The coolant level should drop once it does. Once everything is nice and hot you can shut the engine off and restart it (maybe 5 times?) which can sometimes help to "burp-out" air that's trapped in the system

:thinking:
 
What makes you so sure that your temperature gun is accurate? To make sure the temp gun was accurate; I also used a temp prob used for cooking food. Both temp devices were w/in 5 degrees of each other.

What temperature t-stat are you currently running?
I think 160 or 170. I took the rad cap off and let the engine idle for 20 mins. At around 165 the coolant level dropped a bit.

Are you sure it's really opening at it's rated temperature? If you still have that pan of water boiling on the stove, you can use it again to check the t-stat for proper operation. I haven’t removed the t-stat yet. I will probably remove it next and try and try this out.

What about the radiator cap? Is it in good working order..
Its a brand new 16 lb cap.

I think there might be something going on with an air pocket in the cooling system too Yesterday I removed the cap and started it and let it run for 15 mins. I repeated this process five times. The first time I did this, there were some bubbles that started to come up, however once the engine got warm, the bubbles disappeared. The one thing I did notice is when the engine was running, the coolant level would drop about an inch and stay there until I turned off the engine. Then the coolant would rise back up. Is this normal?

After I did all this, I ran the truck back up into the hills and the temp gauge stayed in the middle. The engine block was around 170. Now outside temp were only around 85. Today is supposed to be in the high 90's, so after work today I'll take it out again.
 
Keep in mind that the engine SHOULD operate at whatever temperature matches your thermostat....that is the way it's designed to work.

A 160-170F thermostat sounds a bit low. Most of our engines run more like 185-195 t-stats usually. Remember, if the coolant is moving too quickly through the system (due to a low t-stat rating, or removed t-stat) you don't allow the hot fluid to spend enough time in the radiator to actually cool down.

It sounds a little backwards, but a low-temp thermostat can actually make your engine run hotter.

Sounds like you burped out some air pockets already...I'd keep working that angle too.


:usaflag:
 
ok so after I had a autometer phantom full sweep mechanical gauge installed along with a 45 degree swivel water neck, the engine still heats right back up to 200. Now however it has been threes hours since I turned the engine off and the engine is still hot with a reading of 140. You guys got any ideas why it is taking the engine so long to cool down. Thanks.
 
What's wrong with a temp of 200???

If you were talking 220 - 230 (or more) I'd say you were overheating. 200 - 210 is a pretty common operating temp. Again, I'll ask if you've changed out your thermostat to something in the 185 - 195 range???

You shouldn't be surprised that the engine is 140 after a couple of hours (what temp do you expect it to be?) There's a lot of iron in that block and plenty of hot coolant in there.....it's going to take a long time for all that heat to dissipate.


:usaflag:
 
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