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Discussion Starter #1
Well, I haven’t been on this site for quite a while. Other than to drop in as an observer, that is. But now I have to come back with some questions on my 2001 Deville with 176,269 miles on it. It started overheating. I have had to add quite a bit of coolant into it, so I began to dread the infamous head gasket failure. Curiously, the car still ran well, but several times it got so hot that the red indicator came on and I had to stop the car to let it cool down and put water or anti-freeze into the reservoir. I did replace the cap for the reservoir.

The car has had a P0420 code for a couple of years, and I just erase it. Sometimes the trouble light stayed off for weeks. But the car started overheating. I looked all over for leaks, and didn’t find any. So I got the kit from O’Reilly’s to do the block test. The videos on YouTube seem to show that the temperature stays OK if the car is just idling. They say to let the car warm up and then do the test. For me, however, the car started to warm up and then get to the point where it needed pressure to stop from boiling. When I used the kit and the fluid, I didn’t have to use the bulb to pull gasses into the test chamber, it did it by itself. And I let it bubble as it wanted for several minutes. The fluid stayed blue. So my first question is did the block test indicate properly, or am I supposed to do it sooner somehow so the pressure in the system doesn’t force gasses into the test chamber?

Besides the P0420 code, the new cap, and the block test, I did a few more things. I know that there might be a blockage in the hose that goes into the top of the reservoir. Apparently, this is supposed to allow bubbles inside the engine to vent when you change the coolant. I checked this hose, and it didn’t flow at all. The video I saw showed that it was always flowing, and in fact the flow would increase when the car was revved up. I got nothing. So I pulled off the “hollow bolt” and looked in it, and it wasn’t clogged and I put it back on. I blew into the hose at that end, and coolant came out of the fitting. Then, I re-attached the hose, went to the other end at the reservoir, and blew into that. I heard a bubbling way down inside the engine. My next question is: does that sound like the purge system is OK? Although the video on YouTube shows coolant flowing, I don’t know if it always does this all the time, or does the thermostat have to be open? I stopped for the day at this point.

So, to recap 😊:

There is the P0420 code and perhaps a clogged catalytic converter.
There is the possibility that I did the block test wrong.
There is the possibility that the purge/hose thingy isn’t working right.
And finally, there is the oil question:

I had just put brand new synthetic oil in the car. With the overheating and so on, the computer now says that I should change the engine oil. But it is synthetic. I have to say that the car never got so hot that it had to use the emergency system where it shuts down or runs in limp home mode. I’m thinking that I should just re-set the counter and maybe change the oil again in 3000 miles or so. The oil doesn’t seem to be discolored, but maybe.

The car is still jacked up. I haven’t stopped the job yet, but I’m hoping that I can get a few checkpoints set up before I try to drive it again.

So: Any ideas? Questions? Snide remarks?
 

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Super Moderator 2003 Deville Base SEMPER PARATUS
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you have multiple problems. I will address only one. If you changed the oil, did you re-set the OLM? If not, the car has no way of knowing you changed oil
 

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Master of the Dark Art of Diagnostics
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regarding the OIL -
IF the engine overheated -
you will automatically get the CHANGE ENGINE OIL message -
BECAUSE oil breaks down with heat -

the computer doesn't know the difference between dino oil and pure synthetic oil -
and there is no EASY way to determine whether the oil - either dino or synthetic HAS been affected -
IT'S YOUR CALL -
either be safe - follow the recommendation - and change the oil -
OR take an chance - and DON'T change the oil - PERSONALLY - I'd change it -

------------------

the PURGE LINE is the ONLY way to eliminate trapped air from the cooling system -
it should ALWAYS have a constant - gentle - flow of coolant -
FROM the hollow bolt TO the serge tank - WHENEVER the engine is running -
REGARDLESS of engine temperature -

the water pump can NOT move air - the result is always overheating -

-------------------

the BLOCK TEST -
the blue fluid reacts to hydrocarbons by changing colors -
the higher the concentration - the more dramatic the color change -
lighter blue - clear - green - yellow -

you are actually testing the AIR inside the SERGE TANK -
this AIR comes from whatever the PURGE LINE eliminated from the cooling system -

IF the PURGE LINE is clogged -
no coolant flows through it - and no trapped air flows through it -
SO - the BLOCK TEST would be totally useless -

LASTLY - to do a valid BLOCK TEST -
AFTER you get the PURGE LINE flowing PROPERLY -
the SERGE TANK needs to be HALF FULL - or slightly LESS -
and you suck the air above the coolant through the blue fluid -
if you suck ANY coolant into the blue fluid - the test is INVALID -
you need to dump out the blue fluid - wash and dry the glass container - and try again -
 

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Discussion Starter #5
regarding the OIL -
IF the engine overheated -
you will automatically get the CHANGE ENGINE OIL message -
BECAUSE oil breaks down with heat -

the computer doesn't know the difference between dino oil and pure synthetic oil -
and there is no EASY way to determine whether the oil - either dino or synthetic HAS been affected -
IT'S YOUR CALL -
either be safe - follow the recommendation - and change the oil -
OR take an chance - and DON'T change the oil - PERSONALLY - I'd change it -

------------------

the PURGE LINE is the ONLY way to eliminate trapped air from the cooling system -
it should ALWAYS have a constant - gentle - flow of coolant -
FROM the hollow bolt TO the serge tank - WHENEVER the engine is running -
REGARDLESS of engine temperature -

the water pump can NOT move air - the result is always overheating -

-------------------

the BLOCK TEST -
the blue fluid reacts to hydrocarbons by changing colors -
the higher the concentration - the more dramatic the color change -
lighter blue - clear - green - yellow -

you are actually testing the AIR inside the SERGE TANK -
this AIR comes from whatever the PURGE LINE eliminated from the cooling system -

IF the PURGE LINE is clogged -
no coolant flows through it - and no trapped air flows through it -
SO - the BLOCK TEST would be totally useless -

LASTLY - to do a valid BLOCK TEST -
AFTER you get the PURGE LINE flowing PROPERLY -
the SERGE TANK needs to be HALF FULL - or slightly LESS -
and you suck the air above the coolant through the blue fluid -
if you suck ANY coolant into the blue fluid - the test is INVALID -
you need to dump out the blue fluid - wash and dry the glass container - and try again -
Hello Basscat. I remember you.
Thanks for the response. I'll work on this tomorrow. The purge line should work by now. I didn't realize that it was the source of the air inside the reservoir. At the moment, I don't think that the coolant got into the test chamber. It was pretty low and I knew it shouldn't be totally full. I'll try again to be sure.

Great answers as usual.

😊
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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Here's your water crossover with the hollow bolt/nipple - the source of purge line flow. That system is a constant bleed from the cooling system high point. That line must flow a small steady stream at idle, increasing somewhat as rpm goes up. Rod out the bolt/nipple to a depth of at least 2.5". You can use a correctly sized twist drill - don't "drill" the nipple - clean it out.

Remember - DO NOT use any sealants or tablets in the cooling system. That all went away in 2006.

If the purge line itself is hopelessly blocked it WILL cause overheats - air bubbles in the coolant and the centrifugal water pump loses pumping ability - replace it with a single piece of correctly sized reinforced rubber fuel line from any parts store - dirt cheap. New screw band clamps.

Water crossover assembled.gif
 

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Discussion Starter #7
Here's your water crossover with the hollow bolt/nipple - the source of purge line flow. That system is a constant bleed from the cooling system high point. That line must flow a small steady stream at idle, increasing somewhat as rpm goes up. Rod out the bolt/nipple to a depth of at least 2.5". You can use a correctly sized twist drill - don't "drill" the nipple - clean it out.

Remember - DO NOT use any sealants or tablets in the cooling system. That all went away in 2006.

If the purge line itself is hopelessly blocked it WILL cause overheats - air bubbles in the coolant and the centrifugal water pump loses pumping ability - replace it with a single piece of correctly sized reinforced rubber fuel line from any parts store - dirt cheap. New screw band clamps.

View attachment 572896
Hello Submariner!

Thanks for the diagram. I re-did the block test and am confident that the engine is good. 🤗 I started the engine and what with basscatt telling me that the flow was to be continuous, I saw today that whatever I did made it work again. The fitting was clean when I looked at it, but I might have felt some resistance when I blew in the reverse direction from the end going into the reservoir. I heard it bubbling deep down inside the engine.

There was something else that happened along the way. I pulled out and re-set all three of the relays for the fans thinking that corrosion might have stopped them from working. At one point, I didn't think that the fans were fast enough. After all, if the engine is hot, the fans should be going to beat the band but they weren't. While I was pulling out the #39 Cooling fan series/parallel relay, I broke the case, so I had to replace it with Master Ignition MPI 2DR1069. The fans run well now and I've taken the car off the jackstands and am about to try it out. We'll see what happens.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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Assuming that no A/C compressor function is set, your (1998 - 2005) fans go to SLOW at 224, FAST at 236. The engines cools to 213, fans turn OFF, the cycle repeats. If some A/C or DEFROST function is set fans run in SLOW all the time. Over 30 mph they usually don't run at all - not needed.

Unless the hood is open you really can't hear SLOW fans. FAST fans are pretty loud.

Here's your 2000 - 2005 N* fan circuit. Note that the 4-blade relays go in - and operate correctly - either way; the 5-blade fits only one way.

Fan control circuit-2000+.gif
 

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Discussion Starter #9
Thanks again for responding. Are they saying that when the a/c gets shut off due to overheating, the fans go slow at that point? That doesn't seem like a good idea. I've driven the car up and down the road a bit and will try to use it this afternoon in normal driving mode. No trouble thus far, and I left it idling for a few minutes with the car in the sun. I'll try to figure out what the fans are doing.
 

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Instead of driving it up and down the road, take it out and give it some good ole WOT. After 2 or 3 of those, get it back home and do the block test again.
 

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Discussion Starter #11
Instead of driving it up and down the road, take it out and give it some good ole WOT. After 2 or 3 of those, get it back home and do the block test again.
Hello Ranger.

Nice to see your post. But today, I drove around about 4 hours and the overheating problem never showed up. So I'm calling it "Fixed." Who would think that among the first things to check, such as the water pump belt, the radiator cap, and leaks, would be that little purge line? I saw that it wasn't purging 😊 but thought it might be that the flow would start sometime after the thermostat opened up.

I'm content with the results of the two block tests I ran. Especially since the car now works. The first one didn't change the color of the fluid either, but the car was heating up and already building pressure in the reservoir. I've never seen any of the characteristics of a failed head gasket, such as smoke from the exhaust. However, it's pretty amazing to know that I boiled off about a gallon and a half of coolant while all this was going on. It's more the nemesis of the head gasket problem than anything. So I'm glad I ran the test. Live and learn I guess.

Nice to see you. And thank you for responding.
 

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Can’t over-emphasize the IMPORTANCE of the PURGE LINE operating correctly!

It is the ONLY way air can get out of the cooling system.


Glad you found / fixed the problem. Hopefully people with this problem in the future will take note of this and save themselves time / expense and CHECK THE PURGE LINE FIRST.

Bjc789
 

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Discussion Starter #13
Can’t over-emphasize the IMPORTANCE of the PURGE LINE operating correctly!

It is the ONLY way air can get out of the cooling system.


Glad you found / fixed the problem. Hopefully people with this problem in the future will take note of this and save themselves time / expense and CHECK THE PURGE LINE FIRST.

Bjc789
Howdy.

Thanks for the post!

Yup. I suspect that some of the foofoo pills I put in it years ago when I changed the water pump did it. It must have been clogged inside the engine though, because the fitting wasn't plugged. If it works again today, I'll be more confident of the fix.

I'm planning on replacing the oil in a bit. I figure that since it was synthetic, it will be OK, but that's not a gamble I want run. I had planed on replacing the transmission fluid and will probably drain out the oil but keep the filter. It also needs a catalytic converter. The old one is a MagnaFlow 46009 and lasted beyond the five year warranty.

This website is extremely valuable. If it hadn't been for this site, I wouldn't have been able to figure out what was wrong. Experienced owners know things the shop manual can't tell you. 🍻 👍
 

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Master of the Dark Art of Diagnostics
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Hello Ranger.

Nice to see your post. But today, I drove around about 4 hours and the overheating problem never showed up. So I'm calling it "Fixed." Who would think that among the first things to check, such as the water pump belt, the radiator cap, and leaks, would be that little purge line? I saw that it wasn't purging 😊 but thought it might be that the flow would start sometime after the thermostat opened up.

I'm content with the results of the two block tests I ran. Especially since the car now works. The first one didn't change the color of the fluid either, but the car was heating up and already building pressure in the reservoir. I've never seen any of the characteristics of a failed head gasket, such as smoke from the exhaust. However, it's pretty amazing to know that I boiled off about a gallon and a half of coolant while all this was going on. It's more the nemesis of the head gasket problem than anything. So I'm glad I ran the test. Live and learn I guess.

Nice to see you. And thank you for responding.
===========================
Who would think that among the first things to check, such as the water pump belt, the radiator cap, and leaks, would be that little purge line? I saw that it wasn't purging 😊 but thought it might be that the flow would start sometime after the thermostat opened up.
YUP - I wonder HOW MANY head gasket failures were actually misdiagnosed simple clogged PURGE LINES -
my guess - more than just a few -
 

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Discussion Starter #15
===========================
Who would think that among the first things to check, such as the water pump belt, the radiator cap, and leaks, would be that little purge line? I saw that it wasn't purging 😊 but thought it might be that the flow would start sometime after the thermostat opened up.
YUP - I wonder HOW MANY head gasket failures were actually misdiagnosed simple clogged PURGE LINES -
my guess - more than just a few -
😊 I'd not want to bet against it. The thing lost so much coolant and so fast, that I didn't think it was the head gasket or the motor wouldn't run much at all. I've been driving around today with no indication of overheating. I sure was puzzled. Thanks again for your answer.

Doing that block test increases my confidence that the car will keep on running for awhile. I've seen 2005s for sale with 60K miles at around $4K. Since I have experienced working on this car, and I've read that the 2005s don't have that head bolt problem, maybe later on I can upgrade. 😎
 

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Discussion Starter #16
Welp. Troubles again...
Yesterday, I was driving around on my route of addresses, and instead of leaving the car running, I turned it off. When I turned it on again, just for less that a second, I saw one bar light up, and then it went away. I kept driving with no overheat condition. This morning, I drove on a trip of about 20 miles there and 20 miles back with no overheating condition. Sooooo...just to be sure, and after the car had cooled down a couple of hours, I took off the reservoir cap and the little hose like before and there was no flow in the hose. Sooo, I went and got my pancake compressor and let it build up to about 50 psi. and back flushed it through the hose from the reservoir into the engine. The fluid in the reservoir bubbled like crazy and splashed coolant all over. U restarted the car, and for a few minutes, the hose flowed, and then it stopped.

Maybe I'm chasing will-o'-the-wisps here, but I thought I'd better report it. The coolant level seemed lower than to begin with too.
 

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2004 Deville
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Sounds like your blowing the clog back into the water passage, take the hose off the nipple on the other end and clean out the nipple.
 

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Discussion Starter #18
That's what I think too. I drove it today and no overheating, but the temperature has dropped at least 10 degrees. I suspect the thing to do is to remove the nipple completely and start the engine and catch the coolant in a funnel or something. What ever is in there seems to be coming back and blocking the nipple inside the engine, because there wasn't any thing inside the nipple when I took it off the first time.

Is anyone reading this missing a pet rat? I think it may be inside my engine.
 

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Yup. I suspect that some of the foofoo pills I put in it years ago when I changed the water pump did it. It must have been clogged inside the engine though, because the fitting wasn't plugged.
The problem with the "foofoo pills" (sealant tabs) is when used with every coolant change. One or two applications should not clog anything up. If the purge line nipple was clear when you checked it, there should be nothing to blow back into the engine.
 

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Discussion Starter #20
The problem with the "foofoo pills" (sealant tabs) is when used with every coolant change. One or two applications should not clog anything up. If the purge line nipple was clear when you checked it, there should be nothing to blow back into the engine.
Yes. True. In my case, I don't see the overheating I saw before, but I'd suspect that there is some kind of something inside the top of the engine that is acting like a flap when it finds a way to try to escape. I'll keep watching the situation and report back if something occurs.

Thanks for your time and responses.
 
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