Coolant in the oil

[240ZMan]

In case you were following my fuel problem I've put it on hold due to this issue.

I've got a slow coolant leak into the engine. I noticed it when my coolant was low with no visible leak and I had steam coming out of the valve cover vent. Coolant is clean, but oil is milky. Front 3 plugs look fine, rear 3 are a bit dark, possibly due to the steam coming out the vent in the air cleaner that's just in front of the rear carb intake. Compression test ranged from 155 to 175#.

I've taken the head off and can't see anything visibly wrong. The N42 head looks fine, and the head gasket looks like new except for being covered in coolant and oil.

FWIW, when I first put this L28 (N42 block) in the car I put my old E31 head on it. When I first started it up I saw a small amount of steam from the valve cover vent, but after about half an hour it went away and I never saw the coolant level drop. A few thousand miles later I switched to this N42 head and never noticed steam again until now. This makes me wonder about the block...

However, when I installed the head the first time I put a little antisieze on the head bolts as one had broken off when I removed them during the initial tear down. This time when I took the bolts off most seemed to not be torqued down as tight as they were when I installed it, which has me wondering if:

1) shoud I have not used antisieze?

2) could the head not being torqued down enough cause a coolant leak but no other problems?

I don't want to just bolt everything back up until I'm sure I've solved the problem.

[Bambikiller240]

I don't think anti-seize is recommended for head bolts. AFAIK, only oil should be used on them. If the bolts loosen up, you could end up with a leak.

When you switched heads, did you use a brand new headgasket?

Are you sure of the condition of the Timing cover? The area of the timing cover behind the waterpump can corrode to the point of a hole developing. Guess what is behind the water pump? (the timing case, where the chain, gears and tensioner, and OIL reside).

[LanceM]

Though it is a lot of work there really isn't much else to do but put it back together and see. I would check what Carl mentioned about the timing cover, and I would check to see that the head is flat, use a new head gasket, and retorque after a heat cycle.

[240ZMan]

Are you sure of the condition of the Timing cover? The area of the timing cover behind the waterpump can corrode to the point of a hole developing. Guess what is behind the water pump? (the timing case, where the chain, gears and tensioner, and OIL reside).

Carl, from the outside all looks fine with it. Is there some way besides removing it to check its condition?

I guess removing it wouldn't be so bad given how much is already off

[Bambikiller240]

Carl, from the outside all looks fine with it. Is there some way besides removing it to check its condition?

I guess removing it wouldn't be so bad given how much is already off

Nope, you have to pull the water pump and look at the timing cover metal behind the water pump. Always use a new gasket when re-installing.

Have a machine shop (or some one familiar with how to do it) check your head for flatness. It only takes a few thousandths of an inch warp to cause problems.

[240ZMan]

Well, today I pulled the water pump and timing cover and I can't see any sign of corrosion or a leak. I pulled the block and while turning it over on the engine stand with the head off a piece of metal fell out of one of the coolant passages. I've attached a picture with several views of it. It's approximately 1/2" x 1/2".

Given I haven't found any obvious sources of the coolant leak and now having found this piece of metal, I'm very suspicious of the block. I'm looking for suggestions on what to do next.

[kinfish]

Before you took the head off did you check the torque (in tightening direction) of all the head bolts? Any less than spec?

Did you inspect the head gasket for signs of water leakage from coolant passages into the cylinders?

Is the photo showing 3 views of one piece or 3 views of 3 pieces? Is your pump impellar intact? Pieces look too hefty to be from impellar?

[240ZMan]

Great call Kinfish, the piece is from an impeller, although this one is complete. I'll guess the PO had one fail and this one is a replacement. So I feel a lot better about this right now.

As for the head bolt torque, I didn't check them before loosening, but they did seem to come off easier than the previous times I've removed them. I just don't know how much of that could be due to having used anti-sieze on them.

The head gasket looks perfect. I've gone over it several times and I just can't see anything wrong with it. It was only one for a few thousand miles and it looks practically brand new.

I'd like to think the coolant leak was due to the head not being torqued down enough. I'll be taking the head in to check for flatness next week.

So my question remains if I should just reassemble, or what?

[Ed]

Like already mentioned. Take the head and the block and have them checked to make sure both mating surfaces are flat. Also have the head pressure tested. You might have a crack that is unnoticeable. Tell the shop your taking this to that you have a coolant leak and that your blowing steam. If both check out o.k. then reassemble using a new gasket. Inspect the threaded holes in the block and make sure that the bolts go in all the way and that there is no binding to cause a false torque reading.

[kinfish]

The piece or pieces have airfoil shapes that appear to have fractured from the rest of the airfoil or root (cannot assess the size of the pieces from photo)., If they are large they may have been from a pump impellar.

Anti-seize compounds do not cause head bolts to become loose. It is critical to insure the mating threads on the bolts and block are clean and free of burrs so you don't consume spec torque trying to overcome friction. You should chase the treads on the block with the proper size tap prior to assembly. The compound is used to minimize corrosion which can lead to excessive breakaway torques and possibly fracture of the bolt. When the final increment of spec torque is applied it creates a preload in the bolt which is the mechanism that prevents the bolt from becoming loose during operating conditions.

If your problem was a leak at the head interface, several scenarios may be culprits:

1) If the bolts were original you should have replaced them with the later turbo head bolts which are improved material and have higher final torque (nominal of 55 ft-lbs).

2) Your bolts may have sustained permanent elongation since the last head removal. They eventually yield after many cycles of time and temperature. When they yield you lose preload and eventually they will become loose in a worst case.

3) Your torque wrench is out-of-calibration.

4) You consumed a portion of the desired spec torque overcoming friction due to dirty or burred threads. This causes preload to be less than optimum.

5) You should torque the head in increments per the sequence in factory manual and do it only when it is bone cold.

6) You should retorque the head after running engine for several hours since head gaskets compress and you may lose preload.

Did you comply with these guidelines on the last head install? I would keep looking for other sources of leaks before you give up and throw it back together.

[Ed]

The piece or pieces have airfoil shapes that appear to have fractured from the rest of the airfoil or root (cannot assess the size of the pieces from photo)., If they are large they may have been from a pump impellar.

Anti-seize compounds do not cause head bolts to become loose. It is critical to insure the mating threads on the bolts and block are clean and free of burrs so you don't consume spec torque trying to overcome friction. You should chase the treads on the block with the proper size tap prior to assembly. The compound is used to minimize corrosion which can lead to excessive breakaway torques and possibly fracture of the bolt. When the final increment of spec torque is applied it creates a preload in the bolt which is the mechanism that prevents the bolt from becoming loose during operating conditions.

If your problem was a leak at the head interface, several scenarios may be culprits:

1) If the bolts were original you should have replaced them with the later turbo head bolts which are improved material and have higher final torque (nominal of 55 ft-lbs).

2) Your bolts may have sustained permanent elongation since the last head removal. They eventually yield after many cycles of time and temperature. When they yield you lose preload and eventually they will become loose in a worst case.

3) Your torque wrench is out-of-calibration.

4) You consumed a portion of the desired spec torque overcoming friction due to dirty or burred threads. This causes preload to be less than optimum.

5) You should torque the head in increments per the sequence in factory manual and do it only when it is bone cold.

6) You should retorque the head after running engine for several hours since head gaskets compress and you may lose preload.

Did you comply with these guidelines on the last head install? I would keep looking for other sources of leaks before you give up and throw it back together.

Yea! :classic: what he said.

[240ZMan]

Thanks for the many suggestions. Last time I did chase the threads with a tap before torquing as well as cleaned the bolt threads and I don't think my torque wrench is off as it's a reasonably new Craftsman and I reset to zero before storing. I don't use it as a breaker bar either

I have used the head bolts several times and I've got a set of turbo bolts to use this time.

I didn't retorque the head after a few hours as the head gasket (Felplro) says right on it that no re-torquing is necessary. I've read contradictory advice on this and wonder how to know when to ignore the manufacturer?

I'll get the head and block deck checked for flatness this week and see what that tells me. Thanks to everyone for the advice.