350 is Overheating

[Fulltimechevy89]

Hi. I have a 77 Chevy K10, 350. It started overheating lately. The weather has been pretty cold, so even after five minutes of running it is already passed the middle mark on temp gauge. I replaced the sending unit, new temp gauge, new thermostat, new radiator cap. The hoses are pretty stiff, but it still gets hot. New coolant as well. Any thoughts?

[bd]

Does the gauge continue to climb past half way when you allow the engine to run?  You probably should verify overheating using an infrared, or thermometer immersed in the radiator for an actual temperature measurement.  Shine a bright flashlight through the radiator core from the backside while peering through the fins to see if there are any obstructions to airflow.  Check the water pump belt tension.  What type of cooling fan and is it pulling adequate air through the radiator?  With the engine running, is there a gradual drop in temperature of ~20° F across the face of the radiator between the passenger and driver sides?  Are there any cold spots or abrupt changes in temperature?  If there is persistent white vapor exiting the exhaust pipe, check for a blown head gasket:

• Substitute a radiator pressure tester for the cap when the engine is cold.  Start the engine and watch the pressure gauge.  How quickly does it build to 15+ PSI?  (DO NOT let it build beyond 20 PSI)!
  
  
• Shut the engine off and watch the gauge.  Does it maintain or lose pressure? 
  
  
• Remove all of the spark plugs and have an assistant crank the engine over a couple of revolutions while you watch the engine from in front of the grille.  To avoid dousing and possible eye injury, don't stand to the side of the engine where you might be sprayed with coolant exiting a cylinder.  If any liquid or mist blows out of a cylinder, there is a breach between that cylinder and the cooling system (e.g., head gasket, crack, etc).  In follow up, run a compression check or cylinder leak down test.
  

[Fulltimechevy89]

Yes it does. So it had been running great since January, we've had a few cold days but still was not getting hot. It is a brand new engine from the crate, new water pump and all. the radiator is original but it doesn't seem to have obstructions of any kind. I installed new temp gauge as well with no change.

The truck starts up, gets warm pretty quickly, which before it was taking longer. I did run it hot a few times because I thought the gauge was bad. No leaks at all, i replaced the upper hose with no change.

A friend of mine said there is supposed to be a thermostat in the fan? And since I live in the mountains it has to be one for the high altitudes?

New fan as well, and new belts.

The needle reaches the middle on idle, and past to the passengers side. before it would stop before the halfway mark on the drivers side.

Thank you or the help and ideas! I am running out of them lol

[Fulltimechevy89]

Also antifreeze pours out slowly when cap is off and it reaches normal temp, no bubbles but is this normal?

[bd]

...the radiator is original but it doesn't seem to have obstructions of any kind....

Is this based on a test, your direct observation, or _________?

...The truck starts up, gets warm pretty quickly, which before it was taking longer....

"Warm" is a relative term.  How many measured degrees at midpoint of the gauge?

...A friend of mine said there is supposed to be a thermostat in the fan? And since I live in the mountains it has to be one for the high altitudes?

Because GM cooling systems are pressurized, it's unnecessary to offer thermostatic fan clutches in special calibrations to compensate for altitude.

...[It has a] new fan as well, and new belts....

Inspect the fan blade pitch to make sure it is "pulling air" through the radiator and not trying to "push air" out the front.  There are CW and CCW rotation fan blades that are nearly identical mirror images of one another.  Verify that someone didn't inadvertently sell you the wrong one.  Recheck fan belt tension.

Also antifreeze pours out slowly when cap is off and it reaches normal temp, no bubbles but is this normal?

This is normal as long as the antifreeze continues to expand and the system is not pressurized.

The best place to start is to verify with an actual quantitative measurement, the temperature of the engine, using an accurate thermometer.  In other words, confirm there is a real world problem before investing excess time and additional money in a ghost repair.  Gauges that aren't calibrated in degrees can be arbitrary.  Once you verify actual engine temperature you will have a known base from which to progress and compare results, eliminating guesswork.  During your diagnoses, avoid making assumptions.  Assumptions have a way of biting! 

In addition to earlier suggestions, check the engine timing with a proper light.  Is there any hissing emanating from the exhaust?

[Fulltimechevy89]

Based on what the gauge says, the temp while it's idling, (after it has warmed up) is around 220-230 degrees. Before it was always a needle space below the middle mark (200 degrees) But I am getting a laser thermometer tomorrow and see, I'm thinking the gauge is acting up. Radiator is great shape, could be a small hole somewhere though.

Also the gauge that I got is 195 degree gauge, it that it's limit or is that the middle mark?

Thanks for the info!

[VileZambonie]

You didn't stuff a rag in the bottom of the radiator or anything like that when you swapped the engine did you? Did you put the Tstat in upside down?

[Fulltimechevy89]

Not that I know of. I've now changed out the t-stat twice. Now I'm thinking someone could have put 180 degree or 160 degree gauge and I got the wrong one. I'm picking up an Laser Thermometer today, so that'll tell me if my gauge is faulty or not

[Fulltimechevy89]

Okay...
So I got my infrared thermostat reader and checked it after I drove it around a little. Pointing it at the sending unit I got a reading of 220-225 degrees. Give or a take a degree or two. Is that normal?

I was going to compare that with my friend's 350 5.7 engine he has in is his Camaro.

Other than that, the gauge still reads pretty high, but it could be off.

I got my new sending unit locally, would it matter what brand I got?
Thank you all for the help so far!

[FlatBlack77]

i am assuming the sending unit is on the side of the block and not near the thermostat housing.

I have one of those infrared thermometers and i noticed that i can get "interference" from other heat sources. so if you are holding the thermometer 6 inches away from the sending unit you may get different readings because the exhaust manifolds are right there. i always put the thermometer as close as i can to what im reading.

so with that being said try again using that way. do the sending unit area, thermostat hosing, upper and lower radiator hoses and even the heater core hoses. just to get an average reading with hopefully it isnt as high as you got before.

do you have a clutch fan? or a fixed fan

[bd]

got my new sending unit locally, would it matter what brand I got?
Thank you all for the help so far!

Gauge discrepancies have been reported using superseded sending units (the OEM part is obsolete).  Read through Correct temperature sender and connector.

Along the lines of Flatblack77's suggestion, try aiming the infrared at the T-stat housing once the engine is up to operating temperature and compare that to the reading at the sending unit.

[Fulltimechevy89]

Thanks bd and Flatblack for your help! Yes my sending unit is one the driver's side of the block, by the manifold.
Agreed, it gets really hot around there. I will try it again.

My dash cluster is pretty old too, I was considering just putting in a pair of new gauges (Oil Pressure and Water pressure) since they would be cheaper than buying new/old gauges.

I have a fan clutch, and both are brand new.

Everything else seems to running as normal, but it would help if I got a correct temp read.

Also the sending unit I got was from BWD, I'm not sure if they are any good???

[VileZambonie]

BWD is fine

Yes my sending unit is one the driver's side of the block, by the manifold.

Your sending unit should be in the drivers side cylinder head, not in the cylinder block or intake manifold.

[Fulltimechevy89]

So after many walks to and from the auto places here, extra parts and extra costs. I called the manufacture of my new temp gauge, and they said my gauge needs the correct sending unit for proper communication between the temp gauge and the sending unit.

So I bought a $3.00 sending unit from the same parts store where I got the temp gauge. Put it in and started the engine and waited for it to warm up and then drove it. All worked perfectly, the gauge needle is back where it was before and is working great!

I had to fix a lot of other parts, but most needed fixing anyway. The thought occurred to me when I found out it wasn't really overheating, but the dialogue between the gauge and the sending unit was off. This happened when I checked it with an infrared thermometer.

Thanks to everyone who helped me with out this!!!