Help Please: Coolant Leak - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Zonaman** · 05-14-2005, 02:20 PM

My 350 has a small coolant leak (about 1 tablespoon per 20 miles). It pools in the depression around the intake maniflod bolt (Edelbrock) nearest the heater hose fitting. The heater hose/fitting does not appear to be the source as I cannot detect any coolant by running my finger around the fitting and tightening the screw clamp around the hose didn't help. It's difficult to see the source of the leak because it's small and only seems to occur when the engine is run at higher speeds. I suspect the bolt itself

Or worse- a hairline crack in the manifold itself. Could anyone tell me how to isolate the cause and what the fix might be?

Thank you.

Bill72BB · 05-14-2005, 03:19 PM

I always try to locate a leak like that right after a long drive and I just turn the truck off.
The pressure will build up after it sits for a couple of minute's you should be able to see it seaping.

Good Luck.

cdowns · 05-14-2005, 03:34 PM

i'd take off the thermo housing , clean it up real good using a new gasket and small amt of hitemp silicone,to the surface as well as bolt threads .
DO NOT OVERTIGHTEN THERMO HOUSING!!! 25-30 ft lbs MAX!!!

**Zonaman** · 05-14-2005, 04:15 PM

Quote:

Originally Posted by cdowns

i'd take off the thermo housing , clean it up real good using a new gasket and small amt of hitemp silicone,to the surface as well as bolt threads .
DO NOT OVERTIGHTEN THERMO HOUSING!!! 25-30 ft lbs MAX!!!

Thank you, I should have mentioned I did this right off. But I have no idea what is on the intake manifold bolt threads. I just made sure these were torqued correctly. Some were loose. I tightened in the correct sequence. Are you supposed to use some type of sealer on these?

cdowns · 05-14-2005, 04:51 PM

yes you should use a good thread sealant on the intake bolts to prevent oil and water leaks on the manifold

**Zonaman** · 05-14-2005, 05:41 PM

OK. If I want to extract that bolt, will I need to drain some coolant out of the block to keep it out of that area while sealing up those threads?

Thanks again, I apprecate the advice.

OhioDan · 05-15-2005, 12:37 AM

Do you have one of those "cool" looking chrome thermostat housings? Seals with an o-ring? That's probably where your leak is. Had one on my engine. Would leak after truck was run. Right where you say yours does. Took it off, thinking it might be cracked. Bought another, and I'll be d@mned if it didn't leak also. Dressed up intake surface, and it still leaked. Took it off, got a steel original housing. Put sealant and gasket on. Torqued it down. NO MORE LEAK! Hope this helps?

MOTHERTRUCKERS · 05-15-2005, 09:44 AM

Drain a little coolant pull your front 2 intake bolts apply sealant and retorque your intake, pull your thermastat bolts add sealant and retorque (retorque spelling check)

**Stocker** · 05-15-2005, 10:42 AM

I have heard that FelPro has a "leakproof" thermostat gasket that seems to be effective. Need to see about getting one myself. HTH

**Zonaman** · 05-15-2005, 06:33 PM

Quote:

Originally Posted by Bill72BB

I always try to locate a leak like that right after a long drive and I just turn the truck off.
The pressure will build up after it sits for a couple of minute's you should be able to see it seaping.

Good Luck.

Did like you said. I'll be damned it is leaking from the thermostat. Looks like the bolt on one side. Used teflon tape on them too. Blue threadlock OK on these bolts? 1" bolts long enough?

Thanks.

cowboy33713 · 05-15-2005, 06:57 PM

Howdy:
Had this same problem on my 67 with it's transplanted 350 using a stock Qjet iron intake. One bolt hole for the thermostat housing on this piece was not "blind", going right through into the water jacket. I used Permatex brand NON-HARDENING gasket sealer on the bolt threads, and the problem was no more. used the same on the gasket as well. That stuff is hard to get off of skin, clothes, surrounding surfaces. Be neat about it, but use enough. Make sure everything is clean and DRY before you start. If you use the hardenable stuff by mistake, future disassembly will be more difficult ( but how often do you do this). The use of an iron housing is also a great idea. Just my $.02.
cowboy33713

**Zonaman** · 05-15-2005, 07:21 PM

OhioDan, I'm using a stock thermostat housing- the type that fits a '75 C10.

As far as sealants for the bolts I've got a bunch of Permatex products: the blue threadlock, the water pump & thermostat hosuing rtv orange high temp rtv, & ultra grey rtv. I usually reach for the waterpump & thermostat tube- but have never used it on the bolts.

**53burb** · 05-16-2005, 08:11 PM

If you have one of the chrome housings, can't you use a gasket on them instead of the o-ring??

05-14-2005, 02:20 PM	#1
Zonaman Senior Member Join Date: May 2004 Location: Chandler, AZ Posts: 516	Help Please: Coolant Leak My 350 has a small coolant leak (about 1 tablespoon per 20 miles). It pools in the depression around the intake maniflod bolt (Edelbrock) nearest the heater hose fitting. The heater hose/fitting does not appear to be the source as I cannot detect any coolant by running my finger around the fitting and tightening the screw clamp around the hose didn't help. It's difficult to see the source of the leak because it's small and only seems to occur when the engine is run at higher speeds. I suspect the bolt itself Or worse- a hairline crack in the manifold itself. Could anyone tell me how to isolate the cause and what the fix might be? Thank you. __________________ 69 C-10 LWB, 350, 700r4, 3.73 posi-traction, front disc brakes. Built for the desert- She can take the heat! Vivat Rex Chevus! Last edited by Zonaman; 05-14-2005 at 02:32 PM.

05-14-2005, 03:19 PM	#2
Bill72BB Thats the Hillbilly way Join Date: Jul 2001 Location: Torrance,Ca Posts: 5,980	I always try to locate a leak like that right after a long drive and I just turn the truck off. The pressure will build up after it sits for a couple of minute's you should be able to see it seaping. Good Luck. __________________ BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen ,

05-14-2005, 03:34 PM	#3
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	i'd take off the thermo housing , clean it up real good using a new gasket and small amt of hitemp silicone,to the surface as well as bolt threads . DO NOT OVERTIGHTEN THERMO HOUSING!!! 25-30 ft lbs MAX!!! __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

05-14-2005, 04:51 PM	#5
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	yes you should use a good thread sealant on the intake bolts to prevent oil and water leaks on the manifold __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

05-14-2005, 05:41 PM	#6
Zonaman Senior Member Join Date: May 2004 Location: Chandler, AZ Posts: 516	OK. If I want to extract that bolt, will I need to drain some coolant out of the block to keep it out of that area while sealing up those threads? Thanks again, I apprecate the advice. __________________ 69 C-10 LWB, 350, 700r4, 3.73 posi-traction, front disc brakes. Built for the desert- She can take the heat! Vivat Rex Chevus! Last edited by Zonaman; 05-14-2005 at 06:47 PM.

05-15-2005, 12:37 AM	#7
OhioDan Registered User Join Date: Apr 2002 Location: New Carlisle, Ohio,USA Posts: 1,404	Do you have one of those "cool" looking chrome thermostat housings? Seals with an o-ring? That's probably where your leak is. Had one on my engine. Would leak after truck was run. Right where you say yours does. Took it off, thinking it might be cracked. Bought another, and I'll be d@mned if it didn't leak also. Dressed up intake surface, and it still leaked. Took it off, got a steel original housing. Put sealant and gasket on. Torqued it down. NO MORE LEAK! Hope this helps? __________________ LIFE AIN'T EASY WHEN YER FAT AND GREASY! GMC= Got More Class! 1970 GMC LWB, Fleetside, 350/4spd, Flowmaster "40's", 2002 GMC 16" Rallies, cowl hood,and added a bunch of options that weren't there when I started.

05-15-2005, 09:44 AM	#8
MOTHERTRUCKERS Registered User Join Date: Dec 1999 Location: BRADENTON FLA Posts: 3,269	Drain a little coolant pull your front 2 intake bolts apply sealant and retorque your intake, pull your thermastat bolts add sealant and retorque (retorque spelling check) __________________ Rest in Peace Ed. Thanks for all the good times.

05-15-2005, 10:42 AM	#9
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,562	I have heard that FelPro has a "leakproof" thermostat gasket that seems to be effective. Need to see about getting one myself. HTH __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

05-15-2005, 06:57 PM	#11
cowboy33713 Senior Member Join Date: Apr 2005 Location: metro Phoenix, AZ Posts: 241	Howdy: Had this same problem on my 67 with it's transplanted 350 using a stock Qjet iron intake. One bolt hole for the thermostat housing on this piece was not "blind", going right through into the water jacket. I used Permatex brand NON-HARDENING gasket sealer on the bolt threads, and the problem was no more. used the same on the gasket as well. That stuff is hard to get off of skin, clothes, surrounding surfaces. Be neat about it, but use enough. Make sure everything is clean and DRY before you start. If you use the hardenable stuff by mistake, future disassembly will be more difficult ( but how often do you do this). The use of an iron housing is also a great idea. Just my $.02. cowboy33713 Last edited by cowboy33713; 05-15-2005 at 06:58 PM.

05-15-2005, 07:21 PM	#12
Zonaman Senior Member Join Date: May 2004 Location: Chandler, AZ Posts: 516	OhioDan, I'm using a stock thermostat housing- the type that fits a '75 C10. As far as sealants for the bolts I've got a bunch of Permatex products: the blue threadlock, the water pump & thermostat hosuing rtv orange high temp rtv, & ultra grey rtv. I usually reach for the waterpump & thermostat tube- but have never used it on the bolts. __________________ 69 C-10 LWB, 350, 700r4, 3.73 posi-traction, front disc brakes. Built for the desert- She can take the heat! Vivat Rex Chevus! Last edited by Zonaman; 05-15-2005 at 07:23 PM.

05-16-2005, 08:11 PM	#13
53burb Registered User Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,004	If you have one of the chrome housings, can't you use a gasket on them instead of the o-ring??



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