RE: 83 F-100, 300 6 cyl., 3 speed, no air.

A couple days ago I took my pickup on a 100 mile trip. Interstate driving on a hot highway. On the 100 mile trip back home the Temp gauge started showing hot. At one point it showed 9/10's of the way to "H." With the needle almost completely on "H," I decided I'd better stop. Which I did. Opened the hood, no steam, nothing boiling over. Water in the overflow container looked normal. Engine didn't seem to be giving off overly hot heat.

Drove on home and the needle seemed to stay about middle of the gauge. Since then, on local driving the needle stays about 1/4...which seems about normal.

Is this thing really overheating, I wonder? Don't want to bother with installing custom gauges right now. Wondering if I can get an oven thermometer, or something, and take a temp reading of the water next time this happens? And
what would be considered "Too Hot" of a temp reading?

 

Well chances are it was not overheating to a bad point. Those dummy gage's give you a big range to play in. According to them it is not bad till you get to the slash mark clear up at the H. Now the one thing to watch even on dummy gage's is for something out of the ordinary. Like if the gage runs about halfway then all of a sudden it starts running at 3/4. Anything that doesn't stay like it has been is something to look at.

You can use a thermometer and stick it in the radiator (careful) right below where the top radiator hose comes in. Or take the temp at the thermostat housing. Either way it should give you a pretty close reading.

 

I found several interesting types of engine thermometers online:
http://www.racetemp.com/
http://www.marshallinstruments.com/catalog/cat4.cfm

Seems this would be a lot easier than installing a custom gauge and more versatile in determining if any temp gauge reading is valid or not. Like, what the heck is the degrees difference between 1/4 and 3/4 on my dummy gauge.

Also, I wonder if anyone has any idea at what temp things would become critical? If the Boiling Point of water is around 212 degrees, would any reservoir overflow container water reading near that be the critical stage?

 

A mechanical temp gage would definitely be better, the dummy gages don't do a whole lot and I don't know what the temp difference would be on the dummy gage.Critical point of the cooling to me would be around 220-225 probably. The coolant in your system is pressurized so it will not boil at 212. Depends on what pressure your system is running as to where the boil or blow off point will be. I usually install mechanical gages on my vehicles just to have an accurate reading of what is going on, the dummy gages are just one step above the dummy lights.

 

When you were running what appeared to be hot, were you climbing a big hill or going extra faster than normal, pushing it hard into a head wind etc?


You might have a small minor leak in a head gasket which can allow hot exhaust gas to leak into your coolant. If not a bad leak, it will only do it when pushing it hard. I had an old inline 6 british car that did this even after replacing the gasket and having the head machined. ( Just poor engineering on bolt placement)

Keep an eye on it the next time you push it and see if it does it again. No big deal right now but it will likely eventually get worse if that is what it is.

If you don't want tyo mess with replacing the gauge, yes, those stick on temp gauges are popular for monitoring various temps on certain components and might serve your needs. You can also watch Ebay and get a hand held temp gauge pretty cheap. I have one that I can touch to any surface and get the exact temp in a matter of seconds and a second one that is a laser where all I have to do it point it at an object and it reads it out. Not as accurate but it gets the job done once you get used to what "normal" is. I swear by Fluke brand but there is a cheaper brand called raytech or ravek or something like that. Like I said, don't pay retail, use Ebay or watch your local discount paper (penny saver, thrifty nickel etc). Usually, eventually someone will be dumping tools cheap. Every day someone decides they are going to be a mechanic and everyday one of them goes out of business and sells thier equipment cheap.

Good Luck,

Lee

 

Thanks fordborn. That will give me some idea when I get one of those engine thermometers.

Yes, pushing it around 70-80 MPH on a hot Interstate Highway. First time I've had this truck on a trip like that. But I have noticed my temp gauge running a noticable bit high at times for no apparent reason...just normal local driving. First I want to confirm if it is really running hot or not. On all my vehicles before, if they ran as hot as the temp gauge said, they blew off steam. Hope it's not the head gasket, but if the motor is truely running hot, I'll keep that in mind.
-Thanks!

 

On my '83 F350 with the 460 engine and the recommended 195 deg. F. thermostat the temperature gauge needle sits squarely in the middle of the "Normal" bar. And the oil pressure gauge reads right in the middle of its "Normal" bar with an actual oil pressure of 50 psi (on a good mechanical gauge). These are not "dummy" gauges, they actually tell you if you have a problem. They are made to have long response time so as not to worry you with short term fluctuations but overall are pretty accurate. Later model trucks like my '99 Ranger do have "dummy" oil pressure gauges that read mid scale if you have ~7psi or more and 0 if less than that, i.e., a "mechanical idiot light".

 

I have to agree but I guess each person's truck is different so maybe some others do have problems with them not being accurate.

Mine seems pretty good as I could see the difference in my gauge when I switched from a 195 degree to a 180 degree thermostat. It used to read high middle and now it is slightly below middle after the change.

Good Luck,

Lee

 

That is totally correct, the newer model "Dummy Gages" are even worse the the older ones. They did that to keep people from panicking on little movements. But as stated earlier they are still just a step above the "Dummy Lights" and can not be depended on to give an accurate reading. For one thing they only have a normal range (which is quite large) instead of actual readings. Therefore they are a good way to see if your engine is still operating as is normal for that engine, but not necessarily tell you what it is actually doing. Thats why I say that if you notice a difference from where your gage has usually been setting then you should check it out and see if you have a problem. Again they are the most basic of gages and not to be trusted for good accuracy but yet can be used to notice something out of place. They are easy to read and see a problem for just about anybody hence the are called "dummy gages". If true readings and accuracy is what you want then go with mechanical gages and do away with the stock dummy gages.

 

my 83 with a 300 six will do this running hard on the highway, check to see if your rad hoses are collapsing. May need to get hoses or get hoses with springs in them to keep them open.

you may also have a partially plugged radiator

 

I already removed my radiator and flushed it out good. Even reverse flushed it until it ran clear. It has the small radiator though. Replaced thermostat 3 times.
Don't think hoses are collapsing, but will check them for stiffness and springs.

 

Did the oil pressure and fuel gauges fluctuate at the same time the temperature gauge did? If so, you may have a instrument voltage regulator going bad or an intermittent ground for it. Also, could be the temperature sending unit.

 

I have noticed that the Oil Pressure gauge and the Temperature gauge often fluctuate together but not the fuel gauge. If Temp gets a little high the oil pressure often does too. Sometimes the Oil Pressure drops to mid-point for awhile and the Temp also drops a little.

Where/what is an Instrument voltage regulator?
Any certain place the gauges are grounded?

I already replaced the oil and temp sending units. Picked up a $5 meat thermometer at Wally World today. Next time it heats up I'll have a look and see if it is for real. Didn't show hot today and the thermometer gave about 180 degrees.

 

It is a little tiny rectangular box looking thing on the circuit card on the back of the gauge cluster and is about 3/8" by 1" or so. It literally Snaps onto the circuit board like a 9 volt battery and has a screw mount on the upper edge.

The ground is done through the connector and then splits off to various places via a confusing array of pigtails and slices to various spots on the dash mounts, steering column, chassis etc.

Good Luck,

Lee

 

My '83 had me sweating today. It's 75 and raining. I had the air on to keep the windshield clear. It was running on medium high speed.

I'm cruising down the highway doing about 65. I notice the temp gauge climbing slowly right on up to H!!! I pull over and check things. Nothing out of the ordinary under the hood. Climb back in the truck, and the gauge is normal. between R and M.

I found this afternoon that if I run the fan on the A/C even on the VENT setting, my temp gauge will climb. I'll be looking for a bad ground tomorrow. I think it could be the ground that runs between the cab and the block. I'll let you know if this is the problem.