454 running hot

[75gmck25]

Sending units from most parts store are incorrect for early 70’s trucks because GM no longer sells the original sensor. For my ‘75 I found the standard products TS6T has the best resistance match to the original, and also the correct nailhead connector.

I also installed an aftermarket mechanical temp gauge (in the thermostat housing) and put the gauge under the dash. Gives me a good confirmation that the dash gauge (which has no numbers) is accurate enough.

 

[YakkoWarner]

I have to admit the harbor freight (and even the slightly "better" one from Lowes) laser thermometer devices don't tend to be overly accurate either - they are very good at finding things like a non-firing cylinder by comparing the temp of the spark plugs or exhaust tubes to each other, but the indicated number seems to be kind of a guess compared to a more accurate physical thermometer.

 

[cobbisbobobbis]

What do you mean?



What I mean is they are notoriously inaccurate.

All the above suggestions are good however, do you really know if it has a problem? Is it boiling over or pushing coolant out? If not, buy a $20 harbor freight temp gun and do some diagnosis first. Feeling how hot or going by the dash cluster isn't reliable. An alternate method is buying a mechanical temp gauge. One poster mentioned the head temperature was higher than the thermostat. Cylinder head will usually run 10-15 degrees hotter than stat. So where temp sender is located has an effect on the reading.

Okay thank you for explaining, I'll go grab a temp gun from Harbor Freight tomorrow or the day after. It is not doing any of that no, I'll verify if it has an actual problem instead of just guessing. I am going to verify if my water pump is failing/if my heater core is clogged or not as well.

Sending units from most parts store are incorrect for early 70’s trucks because GM no longer sells the original sensor. For my ‘75 I found the standard products TS6T has the best resistance match to the original, and also the correct nailhead connector.

I also installed an aftermarket mechanical temp gauge (in the thermostat housing) and put the gauge under the dash. Gives me a good confirmation that the dash gauge (which has no numbers) is accurate enough.

Okay that's a good suggestion I'll have to look into that as well.

I have to admit the harbor freight (and even the slightly "better" one from Lowes) laser thermometer devices don't tend to be overly accurate either - they are very good at finding things like a non-firing cylinder by comparing the temp of the spark plugs or exhaust tubes to each other, but the indicated number seems to be kind of a guess compared to a more accurate physical thermometer.

Good note, thank you.

 

[fast 99]

If not overheating or has any other issue nothing to repair.

Heater hose temp difference could be a restricted core. Temp split of around 20 degrees suggests a problem.

If you want to check the accuracy of a heat gun boil water, read the temp. Be sure to adjust boiling point for altitude, lowers with altitude increase above seal level.

 

[Bextreme04]

@cobbisbobobbis I can't believe no one has mentioned this yet... WE NEED PICS!!!

Ok, now that we have that out of the way, a picture is worth a thousand words. It sounds like there might be nothing wrong... or there could be some hose routing issues. If it isn't boiling coolant, you likely don't actually have an issue.

 

[bucket]

I have to admit the harbor freight (and even the slightly "better" one from Lowes) laser thermometer devices don't tend to be overly accurate either - they are very good at finding things like a non-firing cylinder by comparing the temp of the spark plugs or exhaust tubes to each other, but the indicated number seems to be kind of a guess compared to a more accurate physical thermometer.

The closer you put them to the object you want to measure the temperature of, the more accurate they are. The laser pointer is useless and very misleading.

 

[Grit dog]

Heater core is plugged. You already verified that. Hoses not hot = coolant not circulating. But you could also run the heater if you have any perception of how hot it should be and isn’t.
Water pumps don’t generally slowly fail. Almost never. They work. Then they work but drip then they work but leak a lot. Then you replace it.
You actually have to do some work on this truck to diagnose. Less time on the internet and less gadgets (temp gun). You can get a mechanical temp gauge cheap $16.99 overnight easy install no guessing.
At this point we don’t know that you know what a 240 deg engine feels like compared to 200deg. And you’ve not diagnosed anything to the point of even knowing if it’s running hot. 1 step at at time.

 

[Catbox]

Amazon has inexpensive digital temp gauges.
I put one in my daughters Camaro to verify actual temps versus the stock gauge that is notorious for being wrong.

 

[Bextreme04]

Heater core is plugged. You already verified that. Hoses not hot = coolant not circulating. But you could also run the heater if you have any perception of how hot it should be and isn’t.

We don't even know if this is correct either.... could be connected wrong or any other number of things. Pics would really help, as would verifying the actual coolant temp.

 

[xm20k]

Have you verified flow through rad ie pull cap run it till stat opens look in the rad and visually see flow from cores. I've seen water pumps drop impellers off visually look new spin not leak not make noise, but the impeller was no longer attached to the shaft just sitting in the housing.

 

[Grit dog]

We don't even know if this is correct either.... could be connected wrong or any other number of things. Pics would really help, as would verifying the actual coolant temp.

I suppose anything is possible. But I assumed at least functional hose routing.
Everytime I’ve had cold heater hoses it was due to no flow IE plugged heater core.
Which will realistically raise his temps a smidge or more if there’s more passages/radiator gummed up too.
But bottom line, until the OP does some actual physical diagnosis rather than just internet speculation we won’t know.

 

[Bextreme04]

I suppose anything is possible. But I assumed at least functional hose routing.
Everytime I’ve had cold heater hoses it was due to no flow IE plugged heater core.
Which will realistically raise his temps a smidge or more if there’s more passages/radiator gummed up too.
But bottom line, until the OP does some actual physical diagnosis rather than just internet speculation we won’t know.

I've seen several(especially on big blocks) where they have hooked the heater house line to the connection on the water pump instead of the intake. Then they run the other line to the radiator where it is supposed to go, and now you have two suction lines connected. Now you have no flow, and also the bypass from the intake to the water pump isn't connected like it needs to be... the result is exactly what we are seeing here. No flow through the heater core and overheating engine due to no coolant bypass flow through the engine.

 

[Ricko1966]

Have you verified flow through rad ie pull cap run it till stat opens look in the rad and visually see flow from cores. I've seen water pumps drop impellers off visually look new spin not leak not make noise, but the impeller was no longer attached to the shaft just sitting in the housing.

I twice have run in to water pumps with impeller no longer attached,but they heated to boil over fast. But not many people in overheating situations think about missing impeller. Common belief is if the water pump doesn't leak its good.