flexi New Reader
9/22/13 8:28 p.m.

Anything else that can cause this? Vehicle is 1994 Miata, 111K, 75K with boost. The froth was less last year, but it seems to be a bit worse now. There is some coolant (water right now) loss that requires topping up every two weeks or so. The last two "oil cooler" hoses were replaced after the cursed hose burst 5 minutes from home. No leaks that I can find. Water pump replaced a year ago.

The oil is ok, no coolant or water in it.

I tried to leak test the engine this afternoon, but foolish me, followed the Harbor Freight Tools instructions that came with the leak down tester. The test came out great and I don't believe it. I found reviews on HFT that tell you how to really use it -- alas I did not do what was recommended. So, do another leak down? Start looking for HG kits?

Any other things to look for?

clownkiller HalfDork
9/22/13 8:44 p.m.

Same problem as 2010? Just keep topping fluids, your turbo could be worn. (assuming boosted is not super charged)


I think I may have a HG leak. It isn't very large yet since I don't see it in my tailpipe. I just recently changed the oil, and did not see anything special. However, I do seem to smell a trace of anti-freeze in the air at startup, and when I come to a stop. This is on a boosted 1.8L miata. (since 97)

I slowly loose coolant over time. I've recently replaced the radiator cap and thermostat and never had it grossly overheat. (I replaced both because of minor overheating. No more overheating.) No puddles or other evidence of a leak. The coolant loss is slow compared to a daily check. However, over a week or two, I need to add coolant (well, water right now, since I don't feel like wasting it...) to top it off. The coolant overflow container becomes bone dry. Yes, I do fill the rad and the coolant overflow to the right levels.

Is the definitive method a leak down test? Can I just get http://www.harborfreight.com/cylinder-leak-down-tester-94190.html for the test?

One more question - assuming it is the HG, do you recommend new head studs? New intake and exhaust gaskets?

Knurled UberDork
9/22/13 8:51 p.m.

Turbos can't leak coolant internally... only one place that coolant can be going.

What you should do though is pressure test it with everything stone cold. Lots of times things will only leak when cold and the leak will seal itself when it gets hot.

codrus GRM+ Memberand HalfDork
9/22/13 9:01 p.m.

The coolant hoses on my Miata turbo have basically always leaked a little bit. There are never any puddles because it leaks into a really hot area and instantly vaporizes, so it just manifests as gradually disappearing coolant and a faint coolant smell.

flexi New Reader
9/22/13 9:08 p.m.

In reply to Knurled:

Umm, where is it going? In to coolant?

What do you mean pressure test? leak down cold? or? I'm not quite sure what you mean.

With the unit adapter I have I could just directly apply 100 psi to my cylinder (in 5th gear, brakes on). Check for bubbles in coolant. The leak down tester itself does not seem to operate above 15 psi or so.

I did try cranking with injectors disconnected with the rad cap off. No bubbles.

turbojunker HalfDork
9/22/13 9:13 p.m.

Pretty sure he's referring to pressurizing the cooling system with one of those radiator cap adapter things.

Knurled UberDork
9/22/13 9:14 p.m.

Cooling system pressure test. If you don't have a pressure tester, you can invent one by cleaning the rubber off of a Schrader valve, clamping it into the overflow hose, and using a bike pump to pressurize the cooling system to 15-16psi. It should go past the radiator cap, you can verify that you're pressurizing the system by squeezing the upper hose before and after adding pressure.

Then sit and wait and watch for where it's coming out.

Mystery minor coolant loss is often a small seepage over something hot so the coolant evaporates before it hits the ground, but froth is usually a sign of head gasket or a crack somewhere. Further clue is if there's no problem if you never go into boost. Had a Subaru that acted totally fine until you went over 10psi boost, then it would go past the head gasket.

flexi New Reader
9/22/13 9:17 p.m.

In reply to codrus:

How fast do you lose coolant? Your coolant is 'clear' though, right?

flexi New Reader
9/22/13 9:28 p.m.

In reply to Knurled:

OK. I do have a coolant pressure tester and rad cap tester. Bought it because I thought the rad caps were no good.

So if I do this then I'll be able to find the external leaks like hoses.

If it leaks into the cylinder head, how do I see it? Can you see anything through just the spark plug hole?

Jaxmadine HalfDork
9/22/13 9:37 p.m.

They make another tester for that. When my hg went, it would only leak in boost.

codrus GRM+ Memberand HalfDork
9/22/13 9:46 p.m.
flexi wrote: In reply to codrus: How fast do you lose coolant? Your coolant is 'clear' though, right?

I run something like 80/20 water/green coolant. I don't lose it very fast, maybe I top it up every few months. Then again, the Miata only gets about 3-4K miles a year these days.

44Dwarf SuperDork
9/23/13 7:10 a.m.

See if you can find "Block Test" fluid at the parts store. It's a small bottle you dump in the coolant if it turns blue /purple you have exhaust gasses in the coolant. Should cost about $8

You try the clear 2lt bottle trick too. Fill a 2lt bottle with 1lt or so of water add some puddy / playdoo around the cap end, remove rad cap on cold motor quickly flip the bottle upside down and seal the bottle to the rad with the playdoo. NOW DRILL a small 1/16 to 1/8 hole in the bottles bottom that now at the top. DO NOT forget to drill this hole. Start motor and watch for bubbles to rise up. count the number per minute.

Giant Purple Snorklewacker
Giant Purple Snorklewacker MegaDork
9/23/13 7:36 a.m.
flexi wrote: Any other things to look for?

If a compression and leakdown are good... any chance you just drive the car locally from a cold start, and only drive a few miles and shut it off?

You could just have an oil pan full of condensation and need to get the oil hot enough once in a while to boil it off.

carbon Reader
9/23/13 1:20 p.m.

I've seen thermostats fail and prevent proper operating temp causing condensation in oil as well, usually in colder months. Same with short trips. 5cyl volvos did that alot for some reason.

carbon Reader
9/23/13 1:22 p.m.

change the oil then beat it senselessly, if that cures it, then continue to beat it senselessly you gotta do what you gotta do.

flexi New Reader
9/23/13 9:01 p.m.

In reply to Giant Purple Snorklewacker: I usually drive it for 30 minutes to work. Very few short drives.

flexi New Reader
9/23/13 9:03 p.m.
44Dwarf wrote: See if you can find "Block Test" fluid at the parts store. It's a small bottle you dump in the coolant if it turns blue /purple you have exhaust gasses in the coolant. Should cost about $8

I'll try that. That should be the definitive test for HG leak to coolant, right?

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