Engine coolant temp fluctuation range

[psxpak]

my 71 el camino temp is shooting back and fowarth pretty drastically, I put a 180 thermostat in and it was shooting up and doen from 180 to 210...like... 210>180>210>180 basicaly as the thermostat opened and closed. i swapped it to a 160 and now its 190>160>190>160. i've never seen a temp gauge go up and down so much all my other rigs just sit at the thermostat temp unless im driving them under a load or on a hot day, this thing is doing this cruzing and idle. when i took the thermostat out it just sat at 125 or so, I took the radiator out and flushed it every wich way today wich didn't make a difference. i noticed the lower radiator hose spring was basicaly only part there in the hose so i replaced the hose, I'm thinking of swapping the water pump next. i'm wondering if maybe theres like spring wrapped around the impeller?? anyone ever had an issue like this?

also, i'm safe posting this here right? i can post a pick of my title it sais chevy pickup lol. I do have a 72c/20 and just sold a 72 k/20 on 37 irocs too

[Steeveedee]

Don't post your title, it doesn't help with the problem. Are you sure that the system was completely full of water when the temp had big swings? If the sender isn't immersed it water, it won't read correctly. Since the temp stayed rock steady when there was no thermostat, it makes me think that the system had air in it when there was a thermostat. It can take some time for the system to purge the air out.

[72c20customcamper]

Steve is most likely spot on with it being airbound . I always drill a small or several in the thermostat. This let's the system purge and it really has no effect on its operation except in winter it'll run a little cold

[psxpak]

the coolant was up to the thermostat when i installed it and i also burped it when i flushed the radiator by pulling a plug off of the manifold. (no heater) im definately open to drilling a hole or 2 in the tstat ill give that a shot. i did lete it burp air out of the radiator a few times too in all the process with the cap off.

[leftybass209]

What is the age and condition of your engine and cooling system components?
When did the issue first start showing symptoms?
Did you change the thermostat to fix the problem or routine maintenance?

I agree that drilling a couple holes in the thermostat might fix your problem, and is a great place to start, but i've also never ran across a cooling system for a sbc that took very much time or effort to bleed thoroughly. Especially if you performed the steps you say you've taken, correctly.

That would lead me to believe you're about to stumble upon a moment, or it's another component of the cooling system.

[Caddylackn]

Get one of these when you refill the coolant. They are definitely worth the money https://www.amazon.com/EPAuto-Radiat.../dp/B01I40ZQWE

The funnel connects where the radiator cap fits. You then overfill the radiator above the level of the radiator and start the truck and let it come up to operating temperature and the thermostat opens. The added elevation of the coolant above the radiator puts some fluid pressure on the entire system and allows for a high point to allow the bubbles to rise and get out. This helps purge air bubbles and you can see the air bleed out when running. Don't forget to turn on the heat in the cab to purge the air out of the heater core. I squeeze the bottom radiator hose a few times to get the bubbles started.

This is also the best way to test for a failed head gasket that doesn't leak externally, as in the funnel you will see the combustion pressure cause bubbles in the coolant when running.

When done, you put the plug in the funnel, unscrew from the radiator, and pour the excess back into the jug. Then fill the coolant overflow jug to the proper level for HOT.

[psxpak]

ya honestly ive never seen an issue like this. ive swapped about 7 chevy engines (or rather 7 times sometimes 2 engines back and fowarth) and other than pulling a heater hose to burp ive never had to do anything else besides leave the cap off until the t stat opens. the rig doesnt have a heater. its a wore out old 350 tgat i dont know much about except that the bottom hose is missing alot of the coil spring inside of it. i did notice when the thermostat was out the coolant didnt circulate very fast. it kind of drizzled across 2 small streams. im gonna swap tge pump out next i really think it might be an ussue

[Sheepdip]

How old is the water pump? Sounds more like a cavitation problem to me.

[724jacks]

Where is the temp sending unit? A friend of mine had one installed in the water neck where the temperature vacuum switch would go in a later 70’s sbc. Long story short the temp on his mechanical gauge will fluctuate, like yours is doing. When the thermostat opens temp goes up about 20* then goes back down to 180*. Otherwise probably air in the system
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[psxpak]

sending unit is in the head, i picked up a water pump today and will put it in when hopefully tomorrow

[toolboxchev]

Ok my friend lets see if this is any help.

Had the same problems a few years ago and it seemed I was chasing demons. New parts and same problem

First, is the new water pump with a cast impeller or stamped steel, the cast ones are not that great, AT ALL. I replaced a bad cast unit with a new unit and things did not get much better.

Next lets start with this:

https://www.evapo-rust.com/thermocure/

Or your gunna have to find one of the old acid type cleaners if you have a brass and copper radiator. We will get into more of that later.

Most all of the radiator flush kits/products wont get everything done, I know, I have been there, not once, but over 4 times in the last 15 years.

Did you pull the block drains when you did your last flush?

What pound rating is your radiator cap? Last time out for me I purchased a 16lb cap from Napa and that is part of the key.

Your timing and carb setting are going to play into this so keep us informed, I will be sure to get back as soon as you write back.

Rust scale buildup in water jackets is also a part of this, a small buildup of what most think is a perfectly clean block will affect the cooling systems ability to do its job.

Last part for now, try to get one of these:
https://www.harborfreight.com/121-in...ter-63985.html

You will be able to see live what the actual temp is on the thermostat housing, radiator, on each head, and even the individual header tubes, or manifold.

I was informed by some on this site that the Stant Thermostat for our 350 trucks had a failure rate of 1 in 10 at one point. Those things can float around a bit, took 4 to get my truck to finally settle. If you change from a 160 to a 180 you will find your vehicle will run very different. Its based on todays ethanol fuels. Alcohol likes more engine heat depending on the build to burn correctly, and most of the time more advance in timing to get the fuel burning more thoroughly.

[GASoline71]

Totally off topic question here to the OP... By chance, what color is your '71 El Camino? I sold a citrus green metallic with a black vinyl top '71 El Camino SS back in the late 90's and it ended up in Coos Bay area.

Gary

[psxpak]

It's black. I got it in Brookings Oregon from a guy that bought it in nevada. it was still registered in Arizona. he said he bought the rolling chassis and put the 4 speed and 350 from a 60s camaro in it that he had sitting around.
I put the new water pump on it and in the process of getting the new lower radiator hose off (prying too hard) caused a leak where the tube comes out of the radiator so i had to pull the radiator and re solder it. put it back in and got it all back together and there it sits until tomorrow after work. the old water pump did have some small pieces of the old lower heater hose spring inside of it but didn't seem to me like enough to cause it to not flow sufficient water. now i'm wondering if there might be chunks of that spring in the tubes in the radiator. It reminded me that at one point I drained the radiator by pulling the lower hose and even tho it was full to the top only about 1 gallon of coolant came out like half of the radiator was still full. i'm thinking if it is still doing the same thing tomorrow with the new pump I might pull the radiator out and fill it with some diluted muriatic acid for a couple minutes then flush it with baking soda and water. I have a co worker that always tells me acid is not the answer for everything because im always soaking stuff in and spraying stuff with it. but he's 20 and its easier than wire wheeling or sanding!

[psxpak]

Originally Posted by toolboxchev

Ok my friend lets see if this is any help.

Had the same problems a few years ago and it seemed I was chasing demons. New parts and same problem

First, is the new water pump with a cast impeller or stamped steel, the cast ones are not that great, AT ALL. I replaced a bad cast unit with a new unit and things did not get much better.

Next lets start with this:

https://www.evapo-rust.com/thermocure/

Or your gunna have to find one of the old acid type cleaners if you have a brass and copper radiator. We will get into more of that later.

Most all of the radiator flush kits/products wont get everything done, I know, I have been there, not once, but over 4 times in the last 15 years.

Did you pull the block drains when you did your last flush?

What pound rating is your radiator cap? Last time out for me I purchased a 16lb cap from Napa and that is part of the key.

Your timing and carb setting are going to play into this so keep us informed, I will be sure to get back as soon as you write back.

Rust scale buildup in water jackets is also a part of this, a small buildup of what most think is a perfectly clean block will affect the cooling systems ability to do its job.

Last part for now, try to get one of these:
https://www.harborfreight.com/121-in...ter-63985.html

You will be able to see live what the actual temp is on the thermostat housing, radiator, on each head, and even the individual header tubes, or manifold.

I was informed by some on this site that the Stant Thermostat for our 350 trucks had a failure rate of 1 in 10 at one point. Those things can float around a bit, took 4 to get my truck to finally settle. If you change from a 160 to a 180 you will find your vehicle will run very different. Its based on todays ethanol fuels. Alcohol likes more engine heat depending on the build to burn correctly, and most of the time more advance in timing to get the fuel burning more thoroughly.

It was a cast impeller on the pump, i didnt open the new one just stuck it on there yesterday, 16lb radiator cap. new edelbrock 1406 and new distrubutor bumped up to ping then backed off a bit. we actually JUST got a harbour freight about 6 minutes from my house last tuesday. used to be an hour and 45 minutes to the closest one so i picked up that IR thermometer on the way home yesterday.

[psxpak]

New water pump definitely made a difference in the temp range that it is wandering. still about 30 degrees but now its 140-170 back and forth which at least is right around the 160 t-stat thats in it. I notice that the water doesnt seem like its moving across the top of the radiator as much as im used to seeing, in my other cars ive always seen a pretty good flow when the tstat is open but in this i can see it like flowing up from the bottom ever so slightly. I put about a quarter gallon of acid in the system and ran it about a half hour then flushed the block and radiator like crazy and to my surprise not much of anything came out. one thing im wondering about is the after market gauge is pretty old school, the thing moves fast as hell when the stat opens. are newer temp gauges like a little more stable and slow moving?

[psxpak]

muriatic acid cleaned the system up good, ran a box of baking soda through it and flushed it thoroughly and it is running right around 160.