Pushing coolant out and no other signs of BHG

Another MkIII

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I picked up my car from my friend's shop a couple weeks ago after getting my custom exhaust made, and on the way home noticed some smoke and coolant smell. After a brief inspection, I found it was pushing coolant out the overflow tank which was my first sign of major trouble. The temperature seems to be running normal, aluminum radiator with electric fans, no overheating although that is going off of the stock temp. gauge. I have done the following tests:

Pressure test cooling system: Pressurized to 15 PSI, left for 12 hours. The next morning it was down to 14.5 PSI, but the ambient temperature was cooler by about 15 degrees.

Performed compression test:
1-130
2-150
3-150
4-150
5-150
6-150
This would concern me a lot more but I did a compression test about a year ago and cylinder 1 tested at 120, so its actually up by 10. It still has low miles on the rebuild so it could just be breaking in, but the rings should have seated by now, so I'm not ruling out more serious issues. My timing cover and block were machined, but the cylinders were bored without the timing belt tensioner installed, which could possibly account for the lower compression. To add to this, I performed a wet compression test on cylinder 1 and it now measured 145, which further indicates the piston rings are the source of the low compression.

Checked under oil cap, no milkshake.

I replaced the radiator cap with one from Toyota after reading that some people have had trouble with non-oem. After a test drive of about 3 miles, the issue still persists. It pushed out enough coolant to empty the upper radiator tank. Again, the temperature never spiked or indicated overheating. I drained the oil and there was no coolant in the oil pan and only about 4.7 quarts came out, which is about normal.

The coolant system holds pressure, compression tested acceptable, and its not consuming oil. I would think that if I had a BHG, I would have more symptoms than just pushing out coolant. While I’m not ruling out a BHG, I’m looking at other causes at this point.

-AM3
 

Piratetip

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Have you pressure checked the coolant system while the engine is at operating temp?

FYI the combustion pressure exceeds the coolant pressure by 70x or more.
So you may not be able to replicate the leak in reverse, trying to push 15 psi from the coolant jacket past the fire ring into the combustion chamber.
But the pressure from the combustion chamber even at tiny leak point on the fire ring can easily escape into the coolant jacket.

It sounds like you caught it very early, run it longer in this condition and it will only become worse. (if it is in fact a HG issue)
Pressure checking the coolant system dosn't always tell you the whole story.

Want an instant answer?
Buy or borrow a combustion leak detector and check for exhaust gasses in the coolant system.
 

Another MkIII

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IJ: It was torqued to spec when I rebuilt it, but it wasn't in place when they machined the cylinders. Oversight on my part.

Everyone else: Block test will be the next thing I do. But I'm still curious if there could be another cause besides BHG, although that is still what I consider the most likely cause.

-AM3
 

IJ.

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Another MkIII;2015361 said:
IJ: It was torqued to spec when I rebuilt it, but it wasn't in place when they machined the cylinders. Oversight on my part.

Everyone else: Block test will be the next thing I do. But I'm still curious if there could be another cause besides BHG, although that is still what I consider the most likely cause.

-AM3

That would do it, it's far enough down the bore that it only drops a few PSI cylinder pressure, mine ran like that for years to the point you could see the part of the bore the rings didn't touch as a stain...

36ftlbs.jpg
 

Suprapowaz!(2)

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I've always heard of the not having the idle tensioner not torqued down when machined issue, but seeing is believing. Unfortunately it was an oversight for me as well when I had my block machined. :(
 

Suprapowaz!(2)

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Another MkIII;2015361 said:
But I'm still curious if there could be another cause besides BHG, although that is still what I consider the most likely cause.

-AM3

Did the shop, or you happen to overfill the overflow bottle at some point? Does it do it everyday, and you constantly have to top it off? Or was this a one time deal?
 

IJ.

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Suprapowaz!(2);2015380 said:
I've always heard of the not having the idle tensioner not torqued down when machined issue, but seeing is believing. Unfortunately it was an oversight for me as well when I had my block machined. :(
Pretty sure I was the first to post on the issue way back, I measured a half thou of deflection on the bore when torqued correctly, gets worse the tighter it's bolted down as it's a BIG fine pitch bolt so exerts a lot of force on the thin wall of the block.
 

nosman4

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In addition to testing the coolant for exhaust gases, I would install your pressure tester and start the car and let it idle. Don't pressurize the cooling system, just use it as a gauge and see how quickly the pressure comes up. You can also fill the cooling system and leave the cap off and see if there are bubbles coming out. Is the car up to operating temp before it starts to push coolant out?
 

Another MkIII

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IJ: Yeah, your post was actually the reason I said "Oh crap!" and did a compression test about a year ago. Now that I think of it, it was 2 years ago.

Suprapowaz: I don't believe it wasn't overfilled, but it pushed out enough coolant that once it cooled back down, the overflow tank was empty and the top tank of the radiator had barely any coolant in it. So it lost over a half gallon in 3 miles.

nosman: It doesn't seem to be pushing coolant out until it gets to operating temp.

Also, because its so easy to remove and test, I checked the thermostat and it is operating normal. At this point I'm thinking the block test is just going to confirm what I already know. I've eliminated all other possibilities for coolant to be pushed out, BHG is about the only one left. Hopefully I'll have time to test it and post results tomorrow. Also, if anyone has suggestions for other potential causes, let me know, but I'm not expecting good news tomorrow.

-AM3
 

Another MkIII

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Update: Block test confirmed BHG. Good news is I caught it early enough that the oil wasn't contaminated, so I should be able to get away with just replacing the HG. thanks for the help.

-AM3
 

Nick M

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Another MkIII;2015416 said:
I've eliminated all other possibilities for coolant to be pushed out, BHG is about the only one left.

Assuming you made no assumptions, this is correct logic. Good job. Of course, you already posted your block test, I just wanted to show you did it right, unlike many others here.

When you have eliminated the impossible, whatever remains, however improbable, must be the truth

No matter how bad you don't want it to be true.
 

Another MkIII

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3p141592654;2015652 said:
Understanding why it is leaking would be a good thing to do. Unless you have some reason to believe the gasket was faulty.
That's my main concern, but I'm pretty sure its one of two reasons.

1. When I bought the car, it has a motor that had a hole in the block, but had been rebuilt right before it blew up. I bought a long block on Ebay and rebuilt it including having the deck milled, but because of the recent rebuild, I chose not to machine the head as it seemed good. Lesson learned.

2. Looking back the head gasket was of questionable quality. I didn't go with a MHG, but I didn't use a Toyota one either, I used the HG from the Topline kit I bought. Seemed fine at the time, but knowing what I do now, I would go a different direction.

Lessons learned from my younger and dumber days. In all honesty, as disappointed as I was, I think my dad was more upset by it.

-AM3