Radiator Cap Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Corey'sgotachev · 12-31-2016, 09:53 AM

I have a noob question. I've noticed the coolant level seems to be 2" low all the time. Last time I filled it up, I started truck (350) and waited. The overflow tube had coolant coming out of it but only until the motor is actually warmed up. The coolant stopped coming out then and temp seems fine driving around town.

I want to drive truck to work once in awhile 50 miles one way. Don't want to run it low on coolant.

What cap should I get so that coolant doesn't leak out? Don't think recovery tank was stock. Any recommendations?

Thanks!!! Happy New Year!

**Ironhorse** · 12-31-2016, 10:29 AM

Sounds like it is doing as it should. These old trucks never came from the factory with a coolant overflow / recovery tank. Back in the day, common to fill the radiator to about the 2'' low mark, should be a "coolant level" mark on the radiator tank if radiator is original truck radiator. As the engine warmed to operating temp the coolant expands and excess over the 2'' level was just dumped to the ground via the overflow hose. Some time in the mid to late '70s the Gubment decided that was no longer acceptable with the EPA coming into play and forced auto mfg's to come up with the overflow catch.

It is quite common today to see these trucks with an added coolant recovery tank. I put one on my '71 4x4, easy mod to do. Just be sure you replace the current radiator cap with one that is for a " closed " coolant system. No need to change the thermostat but would be a good time to do so. Then you know all is well.

my56chevytruck · 12-31-2016, 10:36 AM

Quote:

Originally Posted by Corey'sgotachev

I have a noob question. I've noticed the coolant level seems to be 2" low all the time. Last time I filled it up, I started truck (350) and waited. The overflow tube had coolant coming out of it but only until the motor is actually warmed up. The coolant stopped coming out then and temp seems fine driving around town.

I want to drive truck to work once in awhile 50 miles one way. Don't want to run it low on coolant.

What cap should I get so that coolant doesn't leak out? Don't think recovery tank was stock. Any recommendations?

Thanks!!! Happy New Year!

I'm fairly certain this is supposed to be happening but I have a few questions. What cap are you running, is the radiator in the stock location, are your radiator grills above the level of coolant, is this a stock radiator and is there coolant running into your recovery tank and staying there?
Morrie

Corey'sgotachev · 12-31-2016, 03:26 PM

I bought new radiator cap from Napa this morning, a 13lb (?) psi(?). The one I threw away was a 16lb. It was dark and I didn't have a flashlight to look inside. Judging by the amount of coolant I put in, I am guessing level was likely near the fins?
It is hot right now-I will look when it cools down but here's what I witnessed.

Secured cap on full radiator. Started truck (it sounds so wonderful!

) and waited for it to warm up. Before temp gauge started moving, coolant started coming out of overflow hose. It continued coming out until the temp gauge reached 190. At 190, thermostat opened, temp started going down. At that point, the overflow stopped.

If that's the way it's supposed to be, cool! The engine is a crate Goodwrench 350. I'm not sure if radiator is original, but I doubt it as this truck is a 70. How do I tell OE radiator from a replacement? Will a replacement have a "fill to here" mark on it?

Thanks for your help!

geezer#99 · 12-31-2016, 04:25 PM

You don't need a 'fill to here' mark to find out what level your rad runs at.
I usually start about 1 inch down and let it warm up and puke out until it quits. Then let it cool down and check the level again and add about 1/4 inch. It'll puke out a little more and that will likely be the level it likes.
Check it once in awhile just to be sure it's still good. It sometimes takes a few heat cycles to bubble all the air out.
If it ever gets extremely hot it might puke a bit more but just keep an eye on it and fill as necessary.

12-31-2016, 09:53 AM	#1
Corey'sgotachev Registered User Join Date: Apr 2016 Location: Puyallup WA Posts: 48	Radiator Cap Question I have a noob question. I've noticed the coolant level seems to be 2" low all the time. Last time I filled it up, I started truck (350) and waited. The overflow tube had coolant coming out of it but only until the motor is actually warmed up. The coolant stopped coming out then and temp seems fine driving around town. I want to drive truck to work once in awhile 50 miles one way. Don't want to run it low on coolant. What cap should I get so that coolant doesn't leak out? Don't think recovery tank was stock. Any recommendations? Thanks!!! Happy New Year!

12-31-2016, 10:29 AM	#2
Ironhorse Senior Member Join Date: Jul 2001 Location: Wellington, Ks Posts: 10,294	Re: Radiator Cap Question Sounds like it is doing as it should. These old trucks never came from the factory with a coolant overflow / recovery tank. Back in the day, common to fill the radiator to about the 2'' low mark, should be a "coolant level" mark on the radiator tank if radiator is original truck radiator. As the engine warmed to operating temp the coolant expands and excess over the 2'' level was just dumped to the ground via the overflow hose. Some time in the mid to late '70s the Gubment decided that was no longer acceptable with the EPA coming into play and forced auto mfg's to come up with the overflow catch. It is quite common today to see these trucks with an added coolant recovery tank. I put one on my '71 4x4, easy mod to do. Just be sure you replace the current radiator cap with one that is for a " closed " coolant system. No need to change the thermostat but would be a good time to do so. Then you know all is well. __________________ 1971 Chevy 1/2T 4x4 LWB 350 V-8 Was sm465-now 350TH/np205 Tilt, Tach, Towhooks Original Truck AM/FM Wellington, Ks

12-31-2016, 03:26 PM	#4
Corey'sgotachev Registered User Join Date: Apr 2016 Location: Puyallup WA Posts: 48	Re: Radiator Cap Question I bought new radiator cap from Napa this morning, a 13lb (?) psi(?). The one I threw away was a 16lb. It was dark and I didn't have a flashlight to look inside. Judging by the amount of coolant I put in, I am guessing level was likely near the fins? It is hot right now-I will look when it cools down but here's what I witnessed. Secured cap on full radiator. Started truck (it sounds so wonderful! ) and waited for it to warm up. Before temp gauge started moving, coolant started coming out of overflow hose. It continued coming out until the temp gauge reached 190. At 190, thermostat opened, temp started going down. At that point, the overflow stopped. If that's the way it's supposed to be, cool! The engine is a crate Goodwrench 350. I'm not sure if radiator is original, but I doubt it as this truck is a 70. How do I tell OE radiator from a replacement? Will a replacement have a "fill to here" mark on it? Thanks for your help!

12-31-2016, 04:25 PM	#5
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,736	Re: Radiator Cap Question You don't need a 'fill to here' mark to find out what level your rad runs at. I usually start about 1 inch down and let it warm up and puke out until it quits. Then let it cool down and check the level again and add about 1/4 inch. It'll puke out a little more and that will likely be the level it likes. Check it once in awhile just to be sure it's still good. It sometimes takes a few heat cycles to bubble all the air out. If it ever gets extremely hot it might puke a bit more but just keep an eye on it and fill as necessary.



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