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post #1 of 35 (permalink) Old 08-14-2015, 08:09 PM Thread Starter
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Overheated today

My car has always run flawless with zero issues but that ended today.

On my way home from work on the freeway the overheat warning message came on and the temp gauge was all the way up as high as it could go.

I pulled over and the upper rad hose had blown off of the rad neck. Also the lower rad neck is crack open.

So my initial guess is the water pump went bad or the fan stopped working either case would be my best case scenario.

What perplexes me is that the lower neck was nearly all the way off and the upper hose was blown off as well. Could they both had blown at the exact same time? I ask because, just for argument sake we say the neck cracked and caused the fluid lose which led to the overheating, but if the crack was first wouldn't the excess pressure escape through that opening and not letting enough pressure build up to blow the hose off on the top of the radiator?

What's your guys thoughts? Are you guys leaning towards a bad water pump or fan?

2008 G8 V6: Eibach lowering springs, 18" staggered rims, K&N CAI, Series 4400 Flow Master axle backs with FlowMaster tips, radiator cover, tinted tails, silhouette of G8 third brake light.
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post #2 of 35 (permalink) Old 08-14-2015, 08:53 PM
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Not the fan because you were on the highway and that results in the most air flow through the radiator. Guessing water pump.
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post #3 of 35 (permalink) Old 08-14-2015, 09:31 PM
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Not the fan because you were on the highway and that results in the most air flow through the radiator. Guessing water pump.
Yeah water pump or tstat
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post #4 of 35 (permalink) Old 08-15-2015, 11:54 AM
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Yeah water pump or tstat
I agree, Change both.
Make sure theres no obstruction in the way.

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post #5 of 35 (permalink) Old 08-15-2015, 01:46 PM
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What condition was your radiator cap in? That is what should have let out the pressure. In another thread there was speculation that having it tightened all the way down negates the pressure release feature of the cap. In a later redesign GM made it so the cap has a Stop at some point when tightening to allow the pressure release the proper room to operate. Not sure how accurate that theory is though.

From the Service Manual:

Screw On Pressure Cap

The pressure cap is a cap that seals and pressurizes the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring of predetermined strength, which protects the radiator by relieving pressure if it exceeds 15 psi.

The pressure cap allows pressure in the cooling system to build up. As the pressure builds, the boiling point of the coolant goes up as well. Therefore, the coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat moves from the radiator to the cooler, passing air. The pressure in the cooling system can get too high. However, when the pressure exceeds the strength of the spring, it raises the pressure valve so that the excess pressure can escape. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing coolant from the recovery bottle to be sucked back into the cooling system. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator from collapsing.

Last edited by smwalker; 08-15-2015 at 02:29 PM.
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post #6 of 35 (permalink) Old 08-15-2015, 09:53 PM Thread Starter
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Thanks guys.

So today I tore into it.

First the radiator cap was almost impossible to take off. I had to take a rubber mallet to get it to eventually start turning.

What I thought was a leak at the bottom of the radiator turned out just to be the factory holes in the overflow tank to release excess coolant, so no need for a new radiator.

Then I took off the the water pump. The water pump was in prestige condition. The metal propeller looked new, i was able to turn it with zero effort and the bearings were good as well. If I hadn't taken it off myself I would of thought it was new.

So now I moved on to the thermostat, the next logical culprit but I can't find it. Can anyone tell me where it's located and the best way to access/remove it?

2008 G8 V6: Eibach lowering springs, 18" staggered rims, K&N CAI, Series 4400 Flow Master axle backs with FlowMaster tips, radiator cover, tinted tails, silhouette of G8 third brake light.
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post #7 of 35 (permalink) Old 08-15-2015, 10:14 PM
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Think it is right in the neck that attached to the water pump:

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post #8 of 35 (permalink) Old 08-15-2015, 10:39 PM
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Originally Posted by mrathell View Post
First the radiator cap was almost impossible to take off. I had to take a rubber mallet to get it to eventually start turning.
I don't know that lends to my radiator cap root cause scenario. Can you get the cap tested? Know anyone with pressure tester? Would ideally like to test it on the radiator fully seated like it was.
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post #9 of 35 (permalink) Old 08-15-2015, 10:41 PM Thread Starter
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That pic you have must be from a V8 because that's definitely not a 2008 V6 set up.


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Think it is right in the neck that attached to the water pump:


2008 G8 V6: Eibach lowering springs, 18" staggered rims, K&N CAI, Series 4400 Flow Master axle backs with FlowMaster tips, radiator cover, tinted tails, silhouette of G8 third brake light.
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post #10 of 35 (permalink) Old 08-15-2015, 10:48 PM
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That pic you have must be from a V8 because that's definitely not a 2008 V6 set up.
Oh Yes sorry that is V8, I knew you had a V6 and still forgot! LOL

If no one answers I will check the Service manual online. It's just down for site maintenance right now.
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post #11 of 35 (permalink) Old 08-15-2015, 11:59 PM
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I had a thermostat fail 30 years ago in a traffic jam, and the coolant just boiled and barfed out of the overflow tank. When the 'stat fails shut, the steam builds in the heads rapidly. If the pressure got high enough, I'm not surprised both hoses popped off. Hose clamps these days are not what they used to be. But, for you that's better than blowing out a freeze plug or splitting the radiator.

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Last edited by ssn696; 08-16-2015 at 10:15 AM.
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post #12 of 35 (permalink) Old 08-16-2015, 09:40 AM
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They show that the V6 thermostat and housing are mounted on the rear passenger side of the engine block. The service manual has you lowering the whole sub frame down (to gain access) to that item. I seem to remember reading about 1 or 2 members that *were able* to remove it without doing that. It would appear (after removing all the coolant), that you would have to at least remove the entire intake manifold to have a shot at removing that housing and thermostat, along with the rigid heater pipe assembly overlaying it. Maybe those that have done this, can verify that it *can* be done this way.
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post #13 of 35 (permalink) Old 08-16-2015, 10:09 AM
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They show that the V6 thermostat and housing are mounted on the rear passenger side of the engine block. The service manual has you lowering the whole sub frame down (to gain access) to that item. I seem to remember reading about 1 or 2 members that *were able* to remove it without doing that. It would appear (after removing all the coolant), that you would have to at least remove the entire intake manifold to have a shot at removing that housing and thermostat, along with the rigid heater pipe assembly overlaying it. Maybe those that have done this, can verify that it *can* be done this way.
Y'know, there must be a GM designer that wakes up every night laughing his a** off about where he stuck this part.......
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post #14 of 35 (permalink) Old 08-16-2015, 03:47 PM
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Jeesh replacement is an involved procedure. Housing replacement here:

http://imgur.com/a/gbOUI

I think usually if your thermostat was not acting correctly it would have had some check engine lights. Since the pump was in such good shape I would put it all back together and just check for flow. If you got flow then the thermostat is working.
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post #15 of 35 (permalink) Old 08-16-2015, 10:11 PM Thread Starter
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Thanks a million smwalker.

I didn't even attempted to remove the thermostat.

I put it all back together with no new parts installed except for new coolant.

On this 90 degree+ day with the air conditioner blowing on high I test drove it around with zero issues. The temp gauge stayed completely steady on the dot between quarter and the half markings.

It behaved as though the incident never happened.
I will keep a close eye on it for a long time.

2008 G8 V6: Eibach lowering springs, 18" staggered rims, K&N CAI, Series 4400 Flow Master axle backs with FlowMaster tips, radiator cover, tinted tails, silhouette of G8 third brake light.
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post #16 of 35 (permalink) Old 08-17-2015, 02:52 AM
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Just a suggestion you may want to spring for new clamps for the hoses at the radiator. If could be they just got weak. I know for me I plan on doubling up my clamps. Factory spring clamp along with a worm drive on each hose. Belt and suspenders.

Also could you let me know your mileage and if you have ever done any coolant flushes or drain and fills on your radiator? Or was that the factory coolant in there?
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post #17 of 35 (permalink) Old 08-17-2015, 03:04 AM
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As was mentioned, the radiator cap should have let the pressure release before blowing off the hoses. They use to be an in expensive item to replace. I would get a new one.
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post #18 of 35 (permalink) Old 08-17-2015, 11:15 AM Thread Starter
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agreed, ordering a new one today.

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As was mentioned, the radiator cap should have let the pressure release before blowing off the hoses. They use to be an in expensive item to replace. I would get a new one.

2008 G8 V6: Eibach lowering springs, 18" staggered rims, K&N CAI, Series 4400 Flow Master axle backs with FlowMaster tips, radiator cover, tinted tails, silhouette of G8 third brake light.
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post #19 of 35 (permalink) Old 08-17-2015, 11:19 AM Thread Starter
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I'm tending to agree with you smwalker, I say this because when a car over heats and the hose blow, usually there is coolant all over the place, all over the engine and under the hood of the car. On my car there was no sign of coolant anywhere. In fact, if it blew from over heating while I was driving there should of been a huge puff of steam and the sweet smell of coolant. none of this happened.

I'm doubling up my clamps today.


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Originally Posted by smwalker View Post
Just a suggestion you may want to spring for new clamps for the hoses at the radiator. If could be they just got weak. I know for me I plan on doubling up my clamps. Factory spring clamp along with a worm drive on each hose. Belt and suspenders.

Also could you let me know your mileage and if you have ever done any coolant flushes or drain and fills on your radiator? Or was that the factory coolant in there?

2008 G8 V6: Eibach lowering springs, 18" staggered rims, K&N CAI, Series 4400 Flow Master axle backs with FlowMaster tips, radiator cover, tinted tails, silhouette of G8 third brake light.
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post #20 of 35 (permalink) Old 08-17-2015, 10:04 PM
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I'm tending to agree with you smwalker, I say this because when a car over heats and the hose blow, usually there is coolant all over the place, all over the engine and under the hood of the car. On my car there was no sign of coolant anywhere. In fact, if it blew from over heating while I was driving there should of been a huge puff of steam and the sweet smell of coolant. none of this happened.

I'm doubling up my clamps today.
Oh that's interesting so you think you were just low on coolant in the radiator as well? If you could not get the cap off easily then whoever has been doing your oil changes and maintenance has probably not been taking that off (as they don't when a customer bring in a hot car) and filling it. But if they have been keeping the overflow bottle full then that should have been getting sucked in. But if the pressure release and the Vacuum valve were not working correctly on the cap no coolant was passing between the Radiator and overflow bottle.

I would tell you to get a new cap but the updated ones are 20 PSI so there would be even more pressure in the system.

I wonder at what pressure the hoses blow off? That would be a good test to do. Someone might damage their radiator trying it. might have to start a kick starter campaign to encourage someone! LOL
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