LS3 water neck and radiator hose - The 1947 - Present Chevrolet & GMC Truck Message Board Network

6600DURAMAX · 02-22-2023, 05:25 PM

Want to make sure this water neck will fit on the BOTTOM outlet on my LS3

Also - any suggestions for the upper and lower radiator hoses ?

LS short box · 02-22-2023, 05:53 PM

I don't know about the thermostat housing but in regards to the radiator hoses I make a wire pattern and then hit the parts stores. Most will let you look thru them to find what you need.
Just a note. The earlier LS engines had a "fixed" thermostat in the housing. The later LS housings have removeable thermostats.

Joyridin · 02-22-2023, 06:27 PM

That listing shows 1997 - 2020 LS engines, but they changed the thermostat design in 2014 or so. Maybe they made the new ones universal? I had to mill open the diameter where the thermostat sits about .050" on the diameter to get the earlier version to work with the later thermostat.

6600DURAMAX · 02-22-2023, 09:12 PM

Does the thermostat typically go into the lower hose or the upper ?

LS short box · 02-22-2023, 10:17 PM

Always in the lower on LS engines. See pic of my 68 C10 LS swap.
SBC had the stat in the upper hose.

kglowacky · 02-23-2023, 06:13 PM

impressed you got the coil installed without the spindle on.

LS short box · 02-23-2023, 09:54 PM

Good thing about lowering springs that it makes it so much easier to install the spring and then the spindle.

6600DURAMAX · 03-16-2023, 09:48 AM

Back to the top

Thermostat housing is on now just to find the upper and lower hoses

I have searched a few times - seems most suggest the Upper hose to be a Gates 21439 but that has the water neck that comes up and out at like a 40 degree angle, my LS3 has it coming out totally different.

I also couldn't find a clear answer on if the lower hose Gates 21439 had the correct end sizes ?

Neither of the autoparts stores had them in stock or I would have tried

**mongocanfly** · 03-16-2023, 01:37 PM

I've had to splice pieces of hoses on some of the ones I've done..so that could be a option

Joyridin · 03-16-2023, 06:14 PM

I replaced the lower outlet with a straight version. It was on my car, but it works well.

6600DURAMAX · 03-16-2023, 07:09 PM

I think the lower hose will work, ordered a GAtes 20931.... be here next week

**derotoreut** · 03-19-2023, 01:28 PM

Yes that thermostat housing will work. I used the same one on my LS3. I would also use Mr. Gasket Thermostat, PN 6368.

02-22-2023, 05:25 PM	#1
6600DURAMAX Registered User Join Date: Nov 2000 Location: Wheatfield IN, USA Posts: 1,107	LS3 water neck and radiator hose Want to make sure this water neck will fit on the BOTTOM outlet on my LS3 Also - any suggestions for the upper and lower radiator hoses ? Attached Images __________________ 1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years

02-22-2023, 05:53 PM	#2
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 1,918	Re: LS3 water neck and radiator hose I don't know about the thermostat housing but in regards to the radiator hoses I make a wire pattern and then hit the parts stores. Most will let you look thru them to find what you need. Just a note. The earlier LS engines had a "fixed" thermostat in the housing. The later LS housings have removeable thermostats.

02-22-2023, 06:27 PM	#3
Joyridin Registered User Join Date: Sep 2020 Location: Cleveland, Ohio Posts: 478	Re: LS3 water neck and radiator hose That listing shows 1997 - 2020 LS engines, but they changed the thermostat design in 2014 or so. Maybe they made the new ones universal? I had to mill open the diameter where the thermostat sits about .050" on the diameter to get the earlier version to work with the later thermostat.

02-22-2023, 09:12 PM	#4
6600DURAMAX Registered User Join Date: Nov 2000 Location: Wheatfield IN, USA Posts: 1,107	Re: LS3 water neck and radiator hose Does the thermostat typically go into the lower hose or the upper ? __________________ 1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years

02-22-2023, 10:17 PM	#5
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 1,918	Re: LS3 water neck and radiator hose Always in the lower on LS engines. See pic of my 68 C10 LS swap. SBC had the stat in the upper hose. Attached Images

02-23-2023, 06:13 PM	#6
kglowacky Registered User Join Date: Mar 2020 Location: The Woodlands,Tx Posts: 558	Re: LS3 water neck and radiator hose impressed you got the coil installed without the spindle on.

02-23-2023, 09:54 PM	#7
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 1,918	Re: LS3 water neck and radiator hose Good thing about lowering springs that it makes it so much easier to install the spring and then the spindle.

03-16-2023, 09:48 AM	#8
6600DURAMAX Registered User Join Date: Nov 2000 Location: Wheatfield IN, USA Posts: 1,107	Re: LS3 water neck and radiator hose Back to the top Thermostat housing is on now just to find the upper and lower hoses I have searched a few times - seems most suggest the Upper hose to be a Gates 21439 but that has the water neck that comes up and out at like a 40 degree angle, my LS3 has it coming out totally different. I also couldn't find a clear answer on if the lower hose Gates 21439 had the correct end sizes ? Neither of the autoparts stores had them in stock or I would have tried __________________ 1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years

03-16-2023, 01:37 PM	#9
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,579	Re: LS3 water neck and radiator hose I've had to splice pieces of hoses on some of the ones I've done..so that could be a option __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver Last edited by mongocanfly; 03-16-2023 at 07:24 PM.

03-16-2023, 06:14 PM	#10
Joyridin Registered User Join Date: Sep 2020 Location: Cleveland, Ohio Posts: 478	Re: LS3 water neck and radiator hose I replaced the lower outlet with a straight version. It was on my car, but it works well.

03-16-2023, 07:09 PM	#11
6600DURAMAX Registered User Join Date: Nov 2000 Location: Wheatfield IN, USA Posts: 1,107	Re: LS3 water neck and radiator hose I think the lower hose will work, ordered a GAtes 20931.... be here next week __________________ 1972 K5 Build - plans - LS3-6L80e-One Tons..... 1971 CREWMAX Build.....at body shop for couple more years

03-19-2023, 01:28 PM	#12
derotoreut Roto Reuter thats the name... Join Date: Feb 2010 Location: Darien, NY Posts: 1,848	Re: LS3 water neck and radiator hose Yes that thermostat housing will work. I used the same one on my LS3. I would also use Mr. Gasket Thermostat, PN 6368. __________________ ~ Dan My 70 K10 SWB build:http://67-72chevytrucks.com/vboard/s...d.php?t=782232 My 71 SWB build:http://67-72chevytrucks.com/vboard/s...d.php?t=651394 1970 SWB Fleet K10 4X4, 5.3L LM7, 4L60E, Dakota Digital RTX, Vintage Air, Ididit tilt 1971 SWB Fleet C10 - Original SWB Arizona truck, new custom restoration project "Kick out your motor and drive while you're still alive - kick it out!" - Heart 1977



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