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Old 12-25-2005, 11:32 PM
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5.7 Chevy consuming coolant

1999 Suburban 5.7 liter losing coolant at increasing rate. 85,000 miles. Bought with 20K miles in 2000 and have never been able to keep coolant in reservoir -- and have had to add coolant now and again since first purchased. Now having to frequently add coolant and, today observed yellow "froth" in oil filler tube. Valvetrain making lots of noise for 5 minutes (at idle) when engine is cold. Now am attributing this to coolant in engine. (Today ran Amsoil Engine Flush thru engine and changed oil and filter. Intend to at least tighten intake manifold bolts before operating vehicle again and intend to use Amsoil at every oil change from now on to, hopefully, prevent lifter problem.)

Is it likely that tightening the intake manifold bolts will solve coolant consumption problem or will replacing the gasket or undertaking a different fix be necessary? Any suggestions will be appreciated. I've heard that this problem is too common with this engine.

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Old 12-25-2005, 11:42 PM
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It could be the intake manifold gasket. it wouldnt hurt to try and tighten it down. just not too tight because the heads are aluminum. it could also be a cracked head, cracked block, or just simply a head gasket.
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Old 12-25-2005, 11:55 PM
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It sounds like either a head or intake gasket.
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Old 12-26-2005, 06:42 AM
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5.7 losing coolant

I have seen a lot of these leak coolant to the outside, just a very few leaking to the inside. It would be interesting to get a pressure tester on the radiator & watch the rate of pressure loss in a certain time period. Then, tighten your intake bolts & see if there is a difference. If there truly is coolant leaking internally, you could also drain the oil & let it sit tobe sure it is drained good, then again pressure test the cooling system with the drain plug out- surely if there is an internal leak, it will have drops of coolant coming out of the drain plug hole. If you see that the pressure is dropping on the tester, keep pumping it up. These tests may take time, but it is a kind of scientific way to pre test before opening up the motor.
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Old 12-26-2005, 07:27 AM
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look for white smoke from the exhaust pipe....That would indicate a bad head gasket.....Like you said its getting worse, so you should start seeing smoke if there is any. I had a Chevy van that did that, exept when it would warm up, it would go away, like the heat would expand it and seal it.......so I didn't worry about it.

How quickly is it losing coolant?
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Old 12-26-2005, 07:48 AM
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Those intake gaskets are notorious for deteriorating from some kind of reaction to the dexcool and leaking.

http://www.consumeraffairs.com/autom...m_dexcool.html

I dont know why they decided to change to some new coolant ethylene glycol based has been working just fine for 50+ years. Somehow I suspect its the EPA trying to make us safer.


Coolant in oil is a very bad thing. Small amount of moisture the oil can absorb but that sludge like stuff doesnt pump too good youre flirting with disaster of wiping out the bearings. Dont wait for it to get worse.

Felpro makes a heavy duty intake gasket for the Vortec that is stainless steel reinforced. They still make a cheaper one too so you probably have to ask for it.
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Old 12-26-2005, 08:31 AM
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99% chance it is the intake gaskets. With the L31, it is a matter of when, not if, it starts leaking.

Buy new gaskets from the GM dealer....do not go with aftermarket (Fel-Pro etc). The new design has crush sleeves at the bolt holes. The gaskets are about $80 at the dealership. Part number:89017465
I would also recommend getting the injector upgrade kit while you have the intake off. Get rid of those poppet style POS system. It is a very easy job.

From GMPartsDirect.com.
You can likely get away with not getting the bracket or gasket kit. My gasket was still perfect.


Ext Qty Part # Unit Price Ea.
1..........10489421 *COIL 2.170..............20.82
1..........17113206 SEAL KIT 3.270..........20.38
1..........93441235 *INJECTOR 3.300......188.34
1..........93442096 BRACKET 3.300..........7.06
1..........HANDLING CHARGE...................48.91

...........................................Subtota l: $293.51

...........................................Freight : $8.50
...........................................NC Tax: $0.00
...........................................Core Charge: $0.00
...........................................Misc: $0.00
...........................................Total: $302.01

Tim
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Old 12-26-2005, 11:02 AM
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Quote:
Originally Posted by Greg Latvala
Those intake gaskets are notorious for deteriorating from some kind of reaction to the dexcool and leaking.

http://www.consumeraffairs.com/autom...m_dexcool.html

I dont know why they decided to change to some new coolant ethylene glycol based has been working just fine for 50+ years. Somehow I suspect its the EPA trying to make us safer.


Coolant in oil is a very bad thing. Small amount of moisture the oil can absorb but that sludge like stuff doesnt pump too good youre flirting with disaster of wiping out the bearings. Dont wait for it to get worse.

Felpro makes a heavy duty intake gasket for the Vortec that is stainless steel reinforced. They still make a cheaper one too so you probably have to ask for it.
Dexcool is not the reason for the leaks. The reason is from the gasket that GM used. The composite intake gasket could not keep up with the expanding and contracting of the heads. (If I can find the tech bulletin,I'll post it)
The main reason for the change to Dexcool and other extended life coolants was because people were not and still don't flush their cooling systems as they should.

Last edited by TwistedTrbl; 12-26-2005 at 11:07 AM.
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Old 12-26-2005, 11:10 AM
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I agree with the above. Problem with Dex-cool is it creates little acidic globules when exposed to air. I flushed my system and put in regular green coolant. I am perfectly OK with changing the coolant prior to the 100k miles that the Dex-cool is rated for....
Yeah the original GM gaskets were flawed by design from the factory, the updated GM design is much better. Just remember to not over-torque the bolts (11 ft/lbs, or 15 nM) and snug them up per the correct sequence and used red threadlocking compound and clean the threads in the head with a thread chaser first.
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Old 12-26-2005, 09:44 PM
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Quote:
Originally Posted by Tim240Z
I agree with the above. Problem with Dex-cool is it creates little acidic globules when exposed to air. I flushed my system and put in regular green coolant. I am perfectly OK with changing the coolant prior to the 100k miles that the Dex-cool is rated for....

Also, the Dex-Cool does not last as long as it is rated. In my experience, and the experience of several other techs I know, it still requires replacement after approximately 2 years due to acidity promoting electrolysis.
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Old 12-26-2005, 11:48 PM
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I had a 1999 GMC Sierra that ran the dex-cool, i flushes all that crap out and replaced it with the green and have never had any problems with it.
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