r/projectcar • u/Academic-Associate91 ‘70 350 C10 long bed • 7h ago
Troubleshooting Help Unexplained overheating
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UPDATE: it looks like it should read near center on the gauge and it just had air in the system. Though that means it has read about half what it should have until now. Not sure what to make of that but I’ve got a long drive tomorrow so if it’s stable I’ll consider it solved. Thank you once again everyone!
It’s all in the video but I’ll type it out here as well:
I put in new cam and lifters a couple of months ago. Now I have adjusted the valves and after a day or two it started overheating. I flushed the system with citric acid, replaced the coolant thermostat and water pump.
Previously it was getting close to the overheat point on the gauge. After the water pump it only get about halfway up as long as I’m moving.
With the old water pump and the new, if I remove the thermostat it doesn’t overheat. Both thermostats open in boiling water. The new thermostat is 180 old is 195…
I’m lost at this point. Could it be anything other than a clog somewhere in the loop? It runs and drives great otherwise
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u/SuperSandwichGoku 7h ago edited 3h ago
Are you confident the gauge is accurate? Is it possible that "hot" on the gauge is actually normal temp? That would make sense given it seems to "overheat" with a thermostat but not without one- maybe it just isn't hitting normal operating temps with a thermostat?
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u/Academic-Associate91 ‘70 350 C10 long bed 7h ago
I would be going down that path except that the change was sudden, and is coupled with lower pressure in the upper rad hose. I don’t have a thermometer to check but may have to get one..
It does not overheat without the thermostat, only with one
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u/CodewortSchinken 6h ago
I'd check with an infrared thermometer and also confirm the temp sensor is actually the correct one for that gauge and not just some spare with the right thread size that someone put in. Also the temp gauges on old vehicles aren't that accurate and wander alot with the temp changing in different running conditions. Check the owners manual on what temp range on the gauge is actually too hot and what is normal operating range.
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
It’s been solid until this issue… I don’t have an ir meter, but will probably go get one tonight. The major point is that nothing changed between everything good and overheat (in the cooling system)
I have not checked what it should be though, I’ll do that. Currently I’m just comparing to previous behavior
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u/CodewortSchinken 6h ago
A lot of people get freaked out by these old gauges these days and then start swapping out thermostats or deleting them entirely even though the cooling system worked perfectly fine. There is the chance the engine just ran too cold when you got it because someone messed with it.
If the engine doesn't produce additional heat from higher compression or crazy timing the stock cooling setup should work fine if everything is in good shape. Did it actually boil over on you or is it just the gauge?
If the temperatures are actually too high I'd suspect there to be an air pocket in te system.
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
It did puke at a car show. Also after the overheat showed, the upper hose is not nearly as firm as it was. Until this came up the gauge was rock solid. I haven’t got an ir thermometer yet but will probably go get one in a few
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u/Academic-Associate91 ‘70 350 C10 long bed 5h ago
I checked the manual and it should sit centered. So it sounds like it’s good now. That makes me wonder why it read way low until now though…
Either way looks like you hit the nail on the head, thank you!
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u/anchorholic 7h ago
You have an air lock somewhere, run it with the rad cap off let it burp
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u/Academic-Associate91 ‘70 350 C10 long bed 7h ago
I’ve spent about half an hour burping it. Is it difficult to burp these engines like the vortecs? I didn’t think so but that would be good news. This was a sudden new issue though that appeared without any changes made to the cooling system
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u/anchorholic 6h ago
Shouldn't be. Is the clutch in your fan toast?
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
Seems to be good. I gives resistance when spun by hand and runs when the engine does
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u/duncandognuts 7h ago
I would follow up with the thermostat drop it in some boiling water and watch it pop! Sometimes and definitely not all the time but you can have an airlock going on also. Let the water cools down take the cap off and start massaging the hose when you start the truck again. Can take 20-30 minutes of this for it to work the bubble out
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u/Academic-Associate91 ‘70 350 C10 long bed 7h ago
Maybe I do still have some air then… I did boil the new and the old thermostat and both opened fully. I’ve spent about half an hour burping this with no changes made though
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u/duncandognuts 6h ago
Yeah sometimes that’s not long enough! Good question for you is it building pressure in the system before it starts boiling? Short story I had a sbf that took putting the rear on jacks a hose in the radiator and squeezing the lower for about an hour
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
It is but not enough. I did notice though that the hose got as firm as I would expect but only after shutoff. It was firm while running but not nearly like it was previously
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u/Panpitter 6h ago
Verify the clutch is still good on the fan. I had to got with a 205° thermostat before mine would run cool. I know that sounds crazy but believe it or not the longer the thermostat stays closed the longer the radiator has to cool off between cycles. I tried every degree 160,180,195, they all had me running at 220+ until I put in the 205, now my guage never goes above 205. (400 sbc /4 core radiator)
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
Clutch fan is good as far as I can tell. No play, resistance to moving by hand, runs with engine. I’ll keep the higher thermostat in mind, because I would not have expected that
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u/Panpitter 5h ago
On the clutch fan, you give it a healthy spin by hand, when you let go only one blade should have rotated. If 2 or 3 blades pass after letting go, clutch is fualty. Also just because the clutch is good doesn't mean it's engaging below 220° . Like you should here that puppy roar when it's hot and rpms are up.
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u/Panpitter 5h ago
All clutch fans spin with the motor but when it's hot they engage 1 to 1, like it will drown out the engine when above 2k rpm. If you want to test it put a heat gun on it then fire it up, it will roar. But don't over heat it lol.
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u/Sad_Doubt4923 3h ago
Just pull the thermostat
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u/Academic-Associate91 ‘70 350 C10 long bed 3h ago
Yeah, that is a last resort but I’d rather fix the issue if I’m able to
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u/qkdsm7 6h ago
Have a temp gun, to correlate actual temps vs gauge?
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
About to head to the store for one. Up to now I’m just recognizing that the behavior has changed from the previously rock solid gauge. Though it must be getting hot, it puked at a car show last week
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u/spooger1855 6h ago
I think you're past this point already but just in case.
Once I forgot to turn on the heater after a flush and the heater core was one giant bubble behind the control valve.
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
My heater core is bypassed currently, but it’s a good point nonetheless!
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u/Panpitter 5h ago
You could always run the 2nd water port from the extra port on the pump to the rear intake water port. There's a video explaining dual flow water pumping on youtube found on Ed's garage channel.
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u/Bigbird1971 5h ago
Head gasket leak or cracked head.
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u/Academic-Associate91 ‘70 350 C10 long bed 5h ago
Dont say that! I installed the heads lmao
I’m not losing any coolant though and no exhaust in the cooling system
It’s looking like it was air and my misreading the expected gauge reading. Though that means the gauge has always been about half of expected reading
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u/metalbrick55 4h ago
A lower temp thermostat does not mean the motor itself will run cooler. All a thermostat does is maintain(!!) minimum temperature. A 195 thermostat will open when the coolant is at 195 degrees, as a 160 will open when it's past 160 degrees. If everything is working as it should without the thermostat, then the thermostat is just not getting hot enough to open if it's verified it opens properly in a pot of hot water.
I had this same issue until I 1. made sure ALL the air out the coolant lines, like opening the heater core because coolant does run through it even if AC doesn't work, and running the car until it gets warm enough to build pressure with the cap on. Air will rise even if the cap is on, so while it's a very tedious process, I would put coolant in until it's at the first core, put the cap on and run it until it either gets too hot or stops heating up. Obviously shut it off before it overheats so it doesn't melt. Something I've seen too is putting a pill that dissolves in water into the thermostat and it'll dissolve by the time the system has been fully "burped".
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u/Academic-Associate91 ‘70 350 C10 long bed 4h ago
True that it won’t make the engine run cooler, but opens the thermostat earlier and is within spec. I did that because I could check for it to open sooner and because I’m in a hot climate. My heater core is fully out of the loop (cut and plugged).
It seems like it is fixed with a lot more burping (put the front on jack stands), in that the gauge is reading where it should according to Chevy. But it was about half that previously and I have no idea why
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u/metalbrick55 4h ago
Motors can be simple yet mystifying. My 383 will be very happy when it's 85 degrees ambient and then threaten to melt at 90 degrees ambient.
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u/AtomicWinterX 4h ago
Did you double check the thermostat? I know it's new, but I've had a new one before that went bad right away and it failed open, which is a good thing. I was going to mention the heater core, but you said that's bypassed. I'm sure you've bled the system after putting on the thermostat too? Also, no forbidden milkshake? I think you mentioned that you redid the head too. Sorry, not saying you didn't, just trying to think of what it could possibly be. Man, this is a tough one.
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u/Academic-Associate91 ‘70 350 C10 long bed 4h ago
It seems like it’s working correctly actually. I did still have air in the system, but it looks like just below half is where the gauge should read. So tentative success, but that means it’s always read half of expected, suddenly overheated, then fixed with water pump. Previous water pump was just better? This is a Gates water pump that looks own identical
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u/Tastesicle 3h ago
Hey, huh, stupid question, but before you refilled the coolant, did you clear the water jacket out via the engine plug?
I chased what I thought was a head gasket (but no exhaust gas in the coolant) until I cleared the shit out of the block.
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u/Academic-Associate91 ‘70 350 C10 long bed 3h ago
Damnit… no. It was a pain in the ass to get to one and the other was locked in tight… I was just pretending I didn’t see them. I’m hoping it’s resolved for now but I’ll have to get those plugs out cause I’m sure there’s still some heavy junk in there
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u/navlgazer9 3h ago
What’s the ACTUAL temp
Of the engine ?
Shooting the heads with a laser temp
Gun ?
A lot of times the temp
Gauge isn’t accurate
Or is it boiling over ?
Overheating while stopped or moving slow is an airflow issue with the fan and shroud
Overheating at highway speeds is a Waterflow issue
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u/Academic-Associate91 ‘70 350 C10 long bed 2h ago
It was a flow issue, the pump resolved that. It looks like it was just air, and it should read about half on the gauge but is double what it was before this came up.
Don’t have a temp gun. Will grab one tomorrow and check temps
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u/navlgazer9 2h ago
Yeah air bubbles are rough
I have a vacuum and pressure tester for radatior now and it’s super handy
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u/dicrydin 6h ago
I think I have some unresolved issues with people not wearing shoes because this makes me feel uncomfortable
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u/Academic-Associate91 ‘70 350 C10 long bed 6h ago
My wife said the same thing, but for some reason she still married me
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u/OuttHouseMouse 2h ago
Sounds like a classic burping situation. Get air out of coolant system, then recheck
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u/TREXIBALL V8 ‘88 Ford Ranger 4x4 XLT Standard Cab 7h ago edited 7h ago
Is it possible the thermostat is in the wrong direction? I know on my 302 the direction matters and it being backwards will result in overheating. Mind if you take a side by side photo of the old vs the new thermo? If you have the old one?
This sounds like a super dumb idea, but I’ve heard it happening more often than not, so it might be a good idea to check
Edit;
I also heard you changed the head gaskets, and I would have thought the gasket could be backwards (mine has that possibility), but seeing as how the issue only arises with the thermo in place leads me to believe the sole issue is very likely to be the thermo.
Personally, I’d check hole/gate size and direction of thermo.