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  #1  
Old 06-15-2010, 09:53 PM
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Pressure on the coolant system.....

Alright this one is a bit odd; I did a search and similar information repeatdly came up. Basically if there is pressure on the coolant hoses overnight then you're looking at a bad head or head gasket. Beyond that I also read about oil in the coolant pointing to a similar situation.

Now that is what I read but this is whats happening.

If i'm cruising on the highway at 65 and accelerate to say 75 the coolant light will pop on for a few seconds until I hold steady at one speed (Even at 75 the light will turn off and the temperature will remain stable) When I get to my destination the coolant line from the radiator to the engine is hard. I did a test on this and checked the hose every few hours once I got home today (3:30) It was hard then but continued to soften over time and less than 6 hours later it was completly soft again. I do not see any oil in the coolant. I'm really not sure what is going on but I hope I didn't damage the head/head gasket a few months back ago when I had that radiator incident.....

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  #2  
Old 06-15-2010, 10:05 PM
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Hello,

You didnt describe having to refill the coolant. I thought the light was just a low coolant level light. Is yours low? If so maybe a small leak or deteriorated rad/reservoir cap? I never like to jump to cracked head or blown headgasket before the simple fixes have been checked or exhausted.

Arlo
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Old 06-15-2010, 10:11 PM
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Originally Posted by lvfast1 View Post
Hello,

You didnt describe having to refill the coolant. I thought the light was just a low coolant level light. Is yours low? If so maybe a small leak or deteriorated rad/reservoir cap? I never like to jump to cracked head or blown headgasket before the simple fixes have been checked or exhausted.

Arlo

We topped off the system a few months back when we replaced the radiator. A week later the light would kick on whenever I was on a particularly sharp and long on-ramp. I put a little more coolant in and it hasn't come on since.

The reservoir cap is only a few years old.
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Old 06-15-2010, 10:14 PM
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I don't know...you probably came across my thread at some point, I had pressure remaining overnight but all tests to my head were fine and I've gone over 1500 miles since then without a problem. All posts immediately suggested a bad head gasket but I was doubtful, I don't think my car woulld still be running if I had a bad head gasket that long ago. Oil in the coolant is evidence of much more of a problem however...

The bottom part of your post sounds like normal operation to me, system builds pressure and then loses it, not sure what is up with the warning light , maybe an air bubble in the system.
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  #5  
Old 06-15-2010, 10:24 PM
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Id say top it off again if it can be and start checking for small leaks at hose connections, radiator (hope not) there is many of them. Fuel heater, aux water pump, heater valve (monovalve), reservoir hoses etc to name a few. Looking for wetness or crusty white residue caused by evaporated coolant. Those would be a simple start and what I would do. Could be a faulty switch or elctrical circuit if you are in fact full of coolant always when it lights up.

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Old 06-16-2010, 03:24 PM
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Originally Posted by lvfast1 View Post
Id say top it off again if it can be and start checking for small leaks at hose connections, radiator (hope not) there is many of them. Fuel heater, aux water pump, heater valve (monovalve), reservoir hoses etc to name a few. Looking for wetness or crusty white residue caused by evaporated coolant. Those would be a simple start and what I would do. Could be a faulty switch or elctrical circuit if you are in fact full of coolant always when it lights up.

Arlo
Well cold/at idle the reservoir is pretty much full. This morning I cleaned up the areas around the cap but I have yet to see any residue. There was some residue there before but I think it go there from when we spilled a bit of coolant when we were filling the system. I'll keep my eye on it though. I'll also be checking all the other areas a little later (I also hope that I don't have to replace the radiator a 3rd time.....) The reservoir low level indicator sensor did send false signals a few years ago but we took it out and cleaned it and it has been fine since.

My main concern is why there is pressure on the system while the car is running and the related annoyance that the light only seems to kick on under highway acceleration.
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Old 06-16-2010, 03:47 PM
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False signals from that little float switch is not all that unusual,I have had it on occasion on my 87 and my son has had it frequently on his 93.He was going to replace the float switch but recently it has been working OK or at least not giving false warnings.
Pressure in the system when the engine is running is normal from the heat/expansion in the coolant,thats why they put on a cap that is designed to hold a certain amount of pressure,for one reason to raise the boiling point of the coolant and also to prevent the build up of steam pockets in areas of the cylinder head. As for holding pressure overnight i dont understand how that could happen as the cooling of the engine would definitly decrease the pressure from what it was at operating temperature and how high the pressure is at normal operating temp is limited by the design of the cap.The cap even has a built in check valve so that if the cooling system gets cold enough and goes below atmospherec pressure it can allow air to enter to keep from sucking the hoses flat.It seems to me that an engine with a cracked head should loose pressure faster than a good one,but thats just me. Don
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Last edited by oldiesel; 06-16-2010 at 04:01 PM.
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  #8  
Old 06-16-2010, 03:54 PM
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Originally Posted by oldiesel View Post
False signals from that little float switch is not all that unusual,I have had it on occasion on my 87 and my son has had it frequently on his 93.He was going to replace the float switch but recently it has been working OK or at least not giving false warnings Don

Well that potentially would take care of the light issue. Still very worried about the pressure on the system though.
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Old 06-16-2010, 08:17 PM
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Originally Posted by oldiesel View Post
False signals from that little float switch is not all that unusual,I have had it on occasion on my 87 and my son has had it frequently on his 93.He was going to replace the float switch but recently it has been working OK or at least not giving false warnings.
Pressure in the system when the engine is running is normal from the heat/expansion in the coolant,thats why they put on a cap that is designed to hold a certain amount of pressure,for one reason to raise the boiling point of the coolant and also to prevent the build up of steam pockets in areas of the cylinder head. As for holding pressure overnight i dont understand how that could happen as the cooling of the engine would definitly decrease the pressure from what it was at operating temperature and how high the pressure is at normal operating temp is limited by the design of the cap.The cap even has a built in check valve so that if the cooling system gets cold enough and goes below atmospherec pressure it can allow air to enter to keep from sucking the hoses flat.It seems to me that an engine with a cracked head should loose pressure faster than a good one,but thats just me. Don
I do not remember who but one of our Members explained why the pressure gets retained.
Under normal cirumstances the hot Coolant expands and there is not too much air (gas) in the system so when the cold Coolant contracts enough that it decreases the pressure in the system and the Check Valve in the Cap opens.
But, when there is a Head Gasket leaking gas into the system the volume and pressure of compressed gas in the system is such that when the cold Coolant contracts and the cold gas contracts there is not enough contraction to relieve enough pressure to cause the check Valve in the Cap to open.
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Old 06-16-2010, 09:13 PM
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Originally Posted by Diesel911 View Post
I do not remember who but one of our Members explained why the pressure gets retained.
Under normal cirumstances the hot Coolant expands and there is not too much air (gas) in the system so when the cold Coolant contracts enough that it decreases the pressure in the system and the Check Valve in the Cap opens.
But, when there is a Head Gasket leaking gas into the system the volume and pressure of compressed gas in the system is such that when the cold Coolant contracts and the cold gas contracts there is not enough contraction to relieve enough pressure to cause the check Valve in the Cap to open.

Hmm so is what i'm describing normal operating conditions? (Pressure on the hoses but it goes down after shutdown?) A faulty sensor would be the best case scenario but I don't want to take any unnecessary chances.
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Old 07-14-2010, 08:26 PM
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I talked to me indy today and I think i'm going to bite the bullet and get the head gasket done. No oil in coolant or anything but there is a lot of pressure on the system and while the pressure does subside overnight I don't want to risk blowing the head. (So about a grand for a new head gasket VS multiple thousands for a new head)

Thoughts and recomendations?
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Old 07-14-2010, 08:33 PM
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IIRC this is a low coolant light, unplug the sensor or repair it. It has nothing to do with temperature. Similarly, there is a low oil light, which has nothing to do with oil pressure. If temperature is fine, and oil pressure is fine, then all you have to do is be sure that the level is correct, then suspect the sensors. You're apparently trying to fix the symptom without finding the cause.
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Old 07-14-2010, 09:28 PM
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Originally Posted by Fulcrum525 View Post
Hmm so is what i'm describing normal operating conditions? (Pressure on the hoses but it goes down after shutdown?) A faulty sensor would be the best case scenario but I don't want to take any unnecessary chances.
yes.
your pressure reporting is normal for any internal combustion engine with a water cooled motor.
if it's still got pressure in the morning, there is a problem,
and if it builds pressure in less than 1 minute at idle there is a problem.
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Old 07-14-2010, 11:03 PM
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Originally Posted by Fulcrum525 View Post
Hmm so is what i'm describing normal operating conditions? (Pressure on the hoses but it goes down after shutdown?) A faulty sensor would be the best case scenario but I don't want to take any unnecessary chances.
Yes. And the sensor's got nothing to do with it, it just picks up coolant level (its a float). If the light goes on and you see plenty of coolant in the overflow tank (it has to get way low to turn the light on legitimately), then it's just a wonky sensor.
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Old 07-14-2010, 11:20 PM
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yes.
your pressure reporting is normal for any internal combustion engine with a water cooled motor.
if it's still got pressure in the morning, there is a problem,
and if it builds pressure in less than 1 minute at idle there is a problem.

How long should it take the pressure to build up at idle under normal operating circumstances?


Also I put coolant into the system a few weeks ago and the light wouldn't come on. Low and behold a few days ago it started flicking on again under acceleration. Now there is a possibility that my SECOND new radiator is actually leaking as there is a cream colored residue along its top edges. I'm probably going to have that one returned again in the near future.

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