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  #1  
Old September 23rd, 2011, 08:00 PM
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barry f
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Head Gasket

I was driving my 90 the other night and the temp gauge climbed up to just below the red. It stayed there (not in the red) for a bit (stop and go). I pulled over and parked for three hours. I then drove the car 25 miles and it never got passed the middle.

I towed the truck to a garage. They said the thermostat was opening as it should and there were no hot spots on the radiator indicating it would be clogged. They said they let the truck run for a half hour sitting and the temp gauge stayed dead in the middle. As soon as they drove it a block the gauge went to the red.

Now they said they tried to check the head gasket but my system is over pressurized and their test failed as coolant kept rushing in for whatever that means.

So does that sound like the head gasket went? If so would you recore the radiator at the same time and do I have to machine the heads? Could it be something else?
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  #2  
Old September 23rd, 2011, 10:07 PM
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It's one of many possibilities, but there are other symptoms to look for. One is if your oil or coolant is starting to get the "coffee with milk" color to it. There are also test kits out there for checking if there are hydrocarbons in the coolant.

Another test is a compression/leakdown test, which I'm surprised they didn't do. This usually spots a blown head gasket pretty easily. Heck, just a compression tester is cheap and easy to use and very useful for this exact situation.

Heck, could also be something as simple as a worn belt on the water pump, low coolant, bad ignition timing, lean mixture, and all those little things.

-Hans
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  #3  
Old September 23rd, 2011, 10:44 PM
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go simple first fan,fan cltch,water pump
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  #4  
Old September 23rd, 2011, 10:51 PM
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sell the truck. you have ruined it with your lack of mechanical ability. go stand in the corner with your back to us
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Old September 23rd, 2011, 11:00 PM
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Fan clutch fine, fan ok, water pump new. Shop claimed my system had a ton of pressure and the couldn't test the head gasket as the tool kept having coolant rush in. They drained a bunch. I am clearly the tool that should stand in the corner
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Old September 23rd, 2011, 11:20 PM
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Quote:
Originally Posted by bjf View Post
Fan clutch fine, fan ok, water pump new. Shop claimed my system had a ton of pressure and the couldn't test the head gasket as the tool kept having coolant rush in. They drained a bunch. I am clearly the tool that should stand in the corner
Sounds like they were testing the coolant system pressure..... but I bet they were testing it from the radiator plug, which is the wrong spot, as it's not the high point.

A cylinder compression / leakdown test is done via the spark plug holes.

-Hans
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  #7  
Old September 23rd, 2011, 11:58 PM
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I agree with Hans, you should have a leak down test. For what it's worth, I had similar symptoms with my D-90. It turned out to be the head gasket was leaking hot gas into the cooling system. I didn't seem to have exhaust in the coolant, per the test, but when we pulled the gasket it was clear to see.
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  #8  
Old September 24th, 2011, 12:03 AM
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Will do. This place wanted to recore radiator to start then go right into head gasket. Couldn't it be a bad sending unit to temp gauge?

Having a friend who works at the dealer do a battery of tests tomorrow. I assume leak down. Is the pressure normal?
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Old September 24th, 2011, 12:37 AM
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Quote:
Originally Posted by bjf View Post
Will do. This place wanted to recore radiator to start then go right into head gasket. Couldn't it be a bad sending unit to temp gauge?

Having a friend who works at the dealer do a battery of tests tomorrow. I assume leak down. Is the pressure normal?

was the truck over heating Barry ?
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  #10  
Old September 24th, 2011, 12:51 AM
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Hey Barry
Remove the expansion tank cap, and run motor to temp, have someone rev the motor and look for a stream of tiny bubbles, or tank spills over. Also check for hydrocarbons in coolant. Radiator shops can test this. Always start with the simplest possibilities and work up from there before you replace anything.
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Old September 24th, 2011, 01:04 AM
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Truck didn't over heat. Weds night I was driving and the temp crept up but not into the red. Almost but not in the red. I parked it for three hours and drove it 20 miles and the gauge never went passed the middle.

Shop says they let it run for 30 minutes at a time and it was in the middle, but as soon as they drove it a block it went into the red.

Shop called me and said it was over pressurized and the radiator and thermostat seem ok yet of course they want to recore it anyway. Something about if I end up doing the head gasket the radiator should be recored anyway.

I said thanks but I am going to tow the truck home. So thats why I am where I am.
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  #12  
Old September 24th, 2011, 08:09 AM
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You can always use one of those infrared temp guns to see what the actual temp is ... Like you said it may be a faulty temp sender, those are pretty cheap and easy to change out.

Does the fan clutch engaging correspond with the rise in temp?

Just trying to to establish if it's actually getting hot or just the gauge / sender playing up.
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  #13  
Old September 24th, 2011, 09:01 AM
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it sounds like they were using a combustion leak detector, which is a tube filled with a liquid regent that reacts (changes color) to the presence of combustion gases in the cooling system. It reads off the vapor in the cooling system not the coolant itself. Your head gasket was blown to the point where it was forcing coolant up into the leak detector, making it impossible to run the test correctly. But, it is safe to say that your HG is blown if it is pushing that much coolant out. The intermittent overheating is caused by a bubble forming in the system from the combustion gasses buildup. When the bubble finally escapes to the top of the expansion tank then the overheating will stop. Then it will start again as another bubble forms. Rinse, repeat. Sometimes the engine will do this without actually overheating, until it has pushed out enough coolant that the engine can no longer cool properly, then it overheats. Alot of owners fins themselves chasing random coolant leaks and have to tighten hose clamps, change radiator caps etc, when the problem is really that the system is trying to hold much higher pressure than it is designed for. I have had a radiator literally split at the seams from this.
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Old September 24th, 2011, 09:17 AM
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Just to add to your misery, it may go deeper than a head gasket. I would certainly give new gaskets a try, but you might find that even after an extensive repair like that, that it will still push gasses into the cooling system. These aluminum v8s, once they go, they're gone. I've been thru 3 in the last 5 years.
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Old September 24th, 2011, 09:25 AM
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How many miles on the truck. When my classic was pressurizing the overflow tank I did the gaskets problem solved. That was at about 117k. I had similar issues and replaced that stupid temp gauge and fan clutch. If you have never done anything to the radiator I would start here. If you have the heads done its a good time to do front cover seals and timing chain at a minimum. Doing head gaskets is stupid easy the hardest part is getting the ps pump off. If you have a stock gauge indicating you're overheating its getting really hot.
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Old September 24th, 2011, 09:32 AM
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I forgot to add in here one more thing you can check.

Pull the plugs. If you're blowing that much pressure into the coolant, it will likely be leaking back into the cylinder as well. That will cause the affected cylinder(s) to effectively be getting steam cleaned, and you'll see the plugs dramatically cleaner.

-Hans
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  #17  
Old September 24th, 2011, 11:43 AM
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Quote:
Originally Posted by Ren Ching View Post
it sounds like they were using a combustion leak detector, which is a tube filled with a liquid regent that reacts (changes color) to the presence of combustion gases in the cooling system. It reads off the vapor in the cooling system not the coolant itself. Your head gasket was blown to the point where it was forcing coolant up into the leak detector, making it impossible to run the test correctly. But, it is safe to say that your HG is blown if it is pushing that much coolant out. The intermittent overheating is caused by a bubble forming in the system from the combustion gasses buildup. When the bubble finally escapes to the top of the expansion tank then the overheating will stop. Then it will start again as another bubble forms. Rinse, repeat. Sometimes the engine will do this without actually overheating, until it has pushed out enough coolant that the engine can no longer cool properly, then it overheats. Alot of owners fins themselves chasing random coolant leaks and have to tighten hose clamps, change radiator caps etc, when the problem is really that the system is trying to hold much higher pressure than it is designed for. I have had a radiator literally split at the seams from this.
This sounds exactly like what he was trying to tell me. This blows. The truck has 68,000 miles. Radiator was cleaned and repaired four years ago. Since then the system has been flushed once and then three months ago the water pump died and truck went in the red for a second but once the pump was replaced all seemed fine.
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Old September 24th, 2011, 01:23 PM
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That's about the milage when I went through my first head gasket. What Ren Ching describes is what was going on with my truck. The head gasket leak was very small but hill climbs or stop-and-go on a hot day were enough to spike the temperature. After the head gasket was replaced, the cooling system on my truck was solid for another 50,000 and then it was time for a new gasket again when it started leaking at the back of one of the heads.

Do the head gaskets, you'll be happy. Having the heads machined is a good idea if you're pulling them off for the gasket renewal. It doesn't cost much and you'll know that you're going to get a good fit.

On the topic of gaskets, Thom Mathie (Muskyman on Discoweb) is a fan of the Cometic gaskets and I trust his knowledge. I didn't have time to order one this time around but I will use one next time, if I don't go 300 TDi first.

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Old September 24th, 2011, 01:28 PM
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Cool thanks. I was actually just planning to let will tillery guide me on what to get.
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  #20  
Old September 24th, 2011, 01:39 PM
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Barry I just went through this and it was the head gaskets. I had other problems so chose to use the opportunity to do a complete rebuild.

For what's it's worth, I started wth another block and heads that were lower miles and better maintained. Did main and rod bearings, machined the heads and I'm ready to drop the new motor in. I'm pretty frugle and did the entire new engine for less than $1000. Picked it up this morning.
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