350 Running warm

79dentside

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Hey guys, I have a Vortec 350 in my 1991 squarebody suburban that runs a touch on the hot side. It runs about 210 degrees, but at long red lights it tends to get peak out at about 215, never anymore. The radiator looks to be new, the fan clutch works, I am also running a shroud.

My 1979 Sierra’s 350 stays super cool, I never have any issues with it. They appear to both have the same stock type set up.
I would like to see the suburban hot idle around 180, any tips?
 

DoubleDingo

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Sounds like the cooling system needs a good cleaning, and/or the fins need to be cleared of debris. You'd be surprised how much stuff can clog the fins, and how much scale can build-up on the inside of the radiator
 

79dentside

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Interesting. The radiator was painted by a previous owner, should I consider that as a possibility?
Other than that, cooling system is like new. Radiator is very clean.

Would like a 180 degree thermostat help the issue?
 

DoubleDingo

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Vortecs are supposed to run the 180* thermostat. If you're running a 195* that could be your problem. I think a 195* requires an auxiliary fan to keep it at 195*, that is how my jeep is. How long has it been since the system was flushed? Did you flush the system after you bought it? When I bought my '81 that was one of the first things I did after getting it home. Then about a year later I cleaned the radiator internally, and the whole system for about 4 days, then did a flush until nothing but clear water came out, and it doesn't overheat at all. I just bought some cooling system cleaner at lunch because it has been 9 years since I did that, and it is overdue.
 

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I have heard but have not verified, that if your mixture is fat on the antifreeze side it will run a tad hotter than a 50/50 mix. My son's truck had what looked like 100% antifreeze when we serviced his cooling system. It ran cooler when we were done, but we replaced everything all at once, so not sure which change made the temp difference. We had to empty and refill his system 5 times before the bright green antifreeze started to look diluted.
 
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DoubleDingo

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I have heard but have not verified, that if your mixture is fat on the antifreeze side it will run a tad hotter that a 50/50 mix. My son's truck had what looked like 100% antifreeze when we serviced his cooling system. It ran cooler when we were done, but we replaced everything all at once, so not sure which change made the temp difference. We had to empty and refill his system 5 times before the bright green antifreeze started to look diluted.
When I bought Crusty Biscuit, the PO ran 100% coolant because he said water rusted the cooling system. I flushed it and ran 50/50 and installed a 3 row and it ran cool around town, but got warm on the highway, yet never boiled over.
 

WP29P4A

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When I bought Crusty Biscuit, the PO ran 100% coolant because he said water rusted the cooling system. I flushed it and ran 50/50 and installed a 3 row and it ran cool around town, but got warm on the highway, yet never boiled over.
I believe he was 100% correct and 50% wrong. If you run ONLY water, it will rust pretty quick and thick. He must have not understood how the product works. I don't think I have ever seen rusty coolant.

If it runs cooler around town and hotter on the highway, isn't that a symptom of the thermostat not holding the coolant in the radiator long enough to cool it?
 

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I could never figure out why it did that, and now it's munched. When it gets back on the road it won't do any of that.
 

Matt69olds

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Pull the shroud, clean between the radiator and A/C condenser. You will be amazed how much crap gets stuck there.

215 isn’t terribly hot, especially sitting at a red light in traffic. If that’s as hot as it gets with a 195 t-stat I wouldn’t worry

A 180 would probably get you down to around 195. Keep in mind, the t-stats tree temp is when the thermostat begins to open.
 

Bextreme04

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210 is the correct temp at the head with a stock 195 thermostat. Before I got all hot and bothered about it, you might want to get a temp gun and see what the temps actually are, since you could have some pretty significant differences between what the gauge reads and what the temp actually is. If it stays steady and you dont get anything boiling over, I wouldn't be worried about it. 50/50 coolant mix, under 12PSI or more of pressure, wont boil until well over 240 degrees.

If it makes you feel better for it to run cooler, switch to a 180 degree t-stat. It wont hurt anything and will run cooler.
 

fast 99

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If using the factory gauge those are indicators not actual gauges and can show slightly off temps. If it isn't pushing coolant out, knocking or boiling especially after hot soak it is likely fine. Get a cheap heat gun. A hotter thermostat will not cause overheating. It only raises the operating temp. I run 195 stats in almost everything without issues.

Just a FYI, straight water does transfer heat better than 50/50 glycol mix. However, the boiling point will be lower and will need to use rust inhibitor.

Most racing orgs do not allow glycol because it is hard to remove from racetracks.
 

79dentside

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Great info guys! I am going to put a new thermostat in it first. Might have a 195 like you all have stated. Radiator is clear, doesn’t have any obstructions. I’ll then flush it. I think the coolant is pretty new, the previous owner had swapped his other 350 into it the suburban not long ago.

One of the trucks has the actual temp number, one is a general range guage.

1979 GMC Sierra 350, never gets above about 160 degrees.
You must be registered for see images attach

1991 GMC Suburban 350, this is the one that hot idles around 210, sometimes up to about 215
You must be registered for see images attach
 
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geocrasher

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I solved my problems with a high flow 180 degree thermostat, new radiator cap, and a coolant flush.
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Albrigap

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Those gauges are far from accurate.
Remove the sender and screw in a quality bourdon bulb temp gauge.
Stick it ahead of the windshield so you can see it and take it for a drive.
I always run 195 degree thermostats and my temp gauge runs higher than yours.
 

Matt69olds

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I bet it you put a thermometer in the radiator fill neck, you will find the coolant temp around 170. I’m betting if you temporarily install a aftermarket gauge with real numbers, the engine will ge around 190. By the time the coolant goes thru the radiator to the filler neck, it will have cooled off to 170ish.

As someone already mentioned, the gauges aren’t all that accurate. It’s best to look at them often enough to get an idea on what’s normal, and know if the gauge suddenly reads differently than expected, something is wrong.

Every square I have had the temp gauge reads in the area range as what yours does.

Keep in mind, the gauge increments isn’t linear. The gauge lower end of the scale starts at 100, it maxes out at 260. If it was linear, the halfway point would be 180, (260 minus 100=160, half of 160 is 80, 100 plus 80 equals 180) the halfway point is actually 210. I’m guessing GM did that for a couple reasons, number on is to minimize customer concerns. Most people know water boils at 212, as long as the gauge stays below 210 people are happy. The other reason is so the gauge has most of the “happy place” on the left side of normal, with the majority of useful info right in the middle of the gauge.
 
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