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HG and Block Test results

5993 Views 18 Replies 6 Participants Last post by  diggler1971
I have 99 Seville STS w/118,000 miles. Car has been losing coolant to the point of flagging the low coolant message, but never overheats, has no white smoke and runs perfect. Recently had to have the cat. converter replaced, due to clog. Muffler shop guy said it looked like coolant or oil had been getting thru to converter. It looked like whitish balls, a little smaller than b.b.s. At this point, I'm thinkin HG, so I did a block test on it today and I'm a little confused about the results. I tried to post a link to pics of test results, but I don't have enough posts for that. The test fluid started llight blue and after 5 minutes of aspirating the tester, with engine warm and running, the fluid changed to a lighter blue (almost clear). I understand that a failed HG should make the fluid turn yellow. Do my results indicate a "slightly" bad HG?
Are there any other tests that I can run to determine if I have a HG failure for sure?

Is there any other failure that will allow coolant into exhaust?

Thanks, Dig
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A HG is the only thing that will put coolant into the exhaust. If you did the test right after adding coolant you could get a false negative. There is another leak down test that is more involved to test the HG's. It's located in the Tech Tips section.

If it does not overheat it might not be a HG unless it is in the very early stages. You might want to try a cooling system pressure test. Rent the tester and pump up the cooling system to 16 psi and let it set. If it is an external leak, it will eventually show itself. Sometime a slow leak will evaporate before it drips, like a leak in the front of the side tank. You can't see it because the condenser is in front of the radiator and the coolant would evaporate as it drips down unless it was a real bad leak. Dried Dex-Cool leaves a whitish chalky telltale residue.
Coolant in the exhaust means that it's getting in the combustion chamber through a failed HG. How quickly is it using coolant?
I haven't driven it much since suspecting HG failure, but it was using about two quarts of coolant every couple hundred miles. This is approximate.
Must be a week for testing HG's. Here's a video I took of a 98 Deville that's in the family. I will be taking over ownership of this in a few months, and its going to be my "new" winter sled. I'll be storing my convertible again for the whole winter.

Anyway here's the video:

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Is it typical for the color change to happen as fast as in the video?
As I said, mine never did change to green or yellow, it did however turn to a lighter shade of blue. My tester was not run off a vacuum line, it came with a bulb like what's on a blood pressure tester, and when I was pumping it, it was pulling alot of bubbles thru the tester. It took 3 to 5 minutes of constant aspiration to achieve the color change that did occur, and did not change any more, even though I continued to pump it for 7 minutes.
I got a coolant pressure tester from AZ last night and I'm gonna go put that on there this morning. I assume I just put the this tester on with the engine cold and not running, pump it up to about 16 pounds and let it sit and see if it holds pressure, and if not, see if I see any leaks. If this tester does not hold pressure, couldn't that be because it is escaping thru a bad head gasket thoough? I'm gonna try it to see if I detect any leaks that are evaporating (burning up in hat parts) when the egine is hot.
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Hit a road block. The tester does not have a threaded adapter to go on the surge tank threads. It's designed for the old style spring loaded rad caps. I've called around and haven't been able to find an adapter yet, so now I'm calling to try to find another place with a press tester that already has the correct adapter. AARRGGHH
Those testers should come with adapters to fit all the different types of caps.

It will not detect a bad HG unless it is pretty bad and by then it should be pretty evident. Remember you are only pumping it up to 16 psi. That is rarely enough pressure to force coolant through an early stage HG leak. Pressures on the other side of the gasket are coming from the combustion chamber and are MUCH higher.
You may have a long wait while doing a block/cooling system pressure test: they are usually inconclusive for the Northstar failed head gasket diagnosis.

Post #6 - If there's any more than trace concentration of exhaust byproduct in the air over the coolant the liquid will turn past green to yellow pretty quickly. From the Lisle #75500 tester kit: "........continue bubbling the fluid for 2 minutes unless the fluid turns yellow sooner........".

Bubbling for 7 minutes may give a false reading.
Well I'm glad to hear that this test may not tell me much, because I've called around and nobody has an adapter or a tester with the correct adapter. I think I'm gonna run the block test again. I don't think I had added coolant recently when I did the first test, but the car had not been run much in the last couple weeks. I drove it about 70 miles yesterday (with no problems and if the level in the surge tank dropped any, from yesterday morning to this morning, it's not a noticable drop) so I'll try it again and see if I get the same results.
Drive it for more than today - a week or so would be better.

Check your coolant level cold, and try to resist the urge to fill above halfway up in the reservoir.
Here are some pics of the block test just now. First, one of test fluid b4 test:

And after exactly 2 minutes of aspiration:

And finally after 5 minutes of aspiration (just to see diff.):

I want to do the leak down test ranger mentioned, but I don't have the materials on hand to do it. So I'm gonna get what I need for that test tommorow. I was avoiding driving the car for fear that I would clog my new converter, however, I think I was overthinking that a bit. I go back to work tomm. and I'm gonna start driving the Seville, which will be around 300 miles in the next 4 or 5 days. I'm also gonna make up a gauge stick for the coolant in the surge tank and check the level each morning, for an accurate measure of just how much coolant I'm losing. Thank you for the comments so far, and what do you guys think about the color change in todays test?
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You're OK: That test is GOOD: no gas in the airspace.

IF you want to go paranoid, do it again in 10 days or so. Then lock the tester in a cabinet and throw away the key. Drive the car.

.............and don't fill that coolant reservoir more than halfway, cold !!! If your reservoir is half black, half translucent, there's a fill note and arrow molded into the tank top and side. The FULL COLD mark is right about the black/clear tank seam.
where did you guys get the coolant tester kit?
Napa has them. Many parts stores that have a tool rental program may have them as well as most online tool sites. I think Lysle has one for half of what Napa wants.
So, here's an update for anyone that read this thread. I monitored the water level over a tank of gas, and, I lost half a gallon of coolant over 300 miles. Then I finally found an adapter (for Fords) that allowed me to put the coolant syst. pressure tester on the car. Doing this, I found a crack in the pass side radiator side tank, near the locator pin on top. I ordered and installed a new radiator yesterday, and now I'm gonna drive and monitor water level again. Hopefully, this is where all the coolant I was losing was coming from.
Sidenote, after getting the radiator replaced, my A/C is not working. I think I may have jarred something loose while fighting with the condensor (trying to get the radiator out). Speaking of that, getting the rad out was a little bit of a pain, but the new one went back in like butter. Overall, not too bad a job to do. So I'm gonna check the freon press. and try to get the A/C back going. It's still hot here in KY.
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