Water in crankcase/oil in radiator

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'97 FZJ80. Spark plugs look good. Going to do compression test next. I rebuilt the motor 17,250 miles ago. Noticed the white milkshake in the radiator today after adding 3/4 gal of water, and also under oil cap. Been noticing coolant loss in the last 3 or 4 weeks. No milkshake until today. 943 miles ago was my last oil change and oil came out looking normal then. Still running smooth. What else could be the problem besides head gasket; oil cooler? O ring in the timing chain cover? Spark plugs 1 through 6 from top to bottom.

20250118_125219.jpg
 
Compression test results on cold engine.
1- 195 psi
2- 195
3- 200
4- 200
5- 195
6- 190 (battery losing charge; suspect?)
 
Well, I took apart the oil cooler assembly, inspected the gaskets, looked for cracks on the cooler (filled with water and left it overnight), and did not see anything that could have leaked. Reassembled with new gaskets and torqued to spec. After 2 days of driving, I noticed steam coming out of the oil filler hole. I plan, next, to take the valve cover off to see if I can locate where the steam is coming from after reaching operating temperatures.
 
cracked/warped head causes oil/water mixing. Common on these. overheat lately? Mine "ran fine" too (at purchase) until summertime hills came calling.
 
cracked/warped head causes oil/water mixing. Common on these. overheat lately? Mine "ran fine" too (at purchase) until summertime hills came calling.
No overheating issues after rebuild. Machined the head and block. Used a Toyota head gasket, too. Will keep an eye on the water level and oil condition for now.
 
No overheating issues after rebuild. Machined the head and block. Used a Toyota head gasket, too. Will keep an eye on the water level and oil condition for now.
Is the milkshake slightly pink or is it brown like chocolate milk?

Ignore the crap on the bottom of the oil fill cap on top of the valve cover.

You're losing coolant or it didn't get filled and burped properly?

Is it possible the contamination is from the rebuild and having oil in the cooling jackets from all the machining? Did the rebuilder properly wash and flush it from the work done?
 
Is the milkshake slightly pink or is it brown like chocolate milk?

Ignore the crap on the bottom of the oil fill cap on top of the valve cover.

You're losing coolant or it didn't get filled and burped properly?

Is it possible the contamination is from the rebuild and having oil in the cooling jackets from all the machining? Did the rebuilder properly wash and flush it from the work done?
I don't think it's contamination from the rebuild. I checked the fluid regularly after the rebuild and was clean. Also, the block was hot tanked at the shop. Everything was clean. No problems for over 17,000 miles. I'll take the valve cover off this weekend and see what I can find.
 
I don't think it's contamination from the rebuild. I checked the fluid regularly after the rebuild and was clean. Also, the block was hot tanked at the shop. Everything was clean. No problems for over 17,000 miles. I'll take the valve cover off this weekend and see what I can find.
Do an exhaust gases test on the radiator to see if you're getting exhaust in there.

Something is missing here. All your observations are not adding up to oil in the radiator.
 
Is there any way oil/tranny fluid could mix in a failing radiator? My 93 has tranny cooler lines at the bottom of my rad.
It could if the line is leaking inside the radiator. Not in my case.
 
Do an exhaust gases test on the radiator to see if you're getting exhaust in there.

Something is missing here. All your observations are not adding up to oil in the radiator.
Well, there's emulsified oil (milkshake) in the radiator. I'm ruling out exhaust gas in radiator based on my compression test. The combustion chamber seems to be sealed.

Here's something interesting going on between cylinder #5 and #6 on to of the head. What's that big hex plug? See the darkened area.

20250131_194328.jpg
 
As an observation from outside, you have stayed in a couple cases "that's not the problem".

I'm not meaning to gouge, but step back a minute and rethink every test you've done. Take nothing for granted.

You have oil in the coolant.
You do not have coolant in the oil.
You are losing coolant.

Where can oil get into the coolant, but coolant cannot get back into the oil?
The oil must be at higher pressure than the coolant.

Where am I losing coolant?

I hate to say it, but I think you may have a cracked cylinder wall. That's why you need to do an exhaust gases test in the coolant.

After you did the oil cooler clean and reseal, how did you flush and clean the cooling system to get the oil out of the radiator, block, heater cores, etc?
Maybe do a static pressure test of the cooling system with the spark plugs out, and scope the cylinders to see if you can find coolant drips. May need to rotate the engine to observe the entire wall in each cylinder.
 
As an observation from outside, you have stayed in a couple cases "that's not the problem".

I'm not meaning to gouge, but step back a minute and rethink every test you've done. Take nothing for granted.

You have oil in the coolant.
You do not have coolant in the oil.
You are losing coolant.

Where can oil get into the coolant, but coolant cannot get back into the oil?
The oil must be at higher pressure than the coolant.

Where am I losing coolant?

I hate to say it, but I think you may have a cracked cylinder wall. That's why you need to do an exhaust gases test in the coolant.

After you did the oil cooler clean and reseal, how did you flush and clean the cooling system to get the oil out of the radiator, block, heater cores, etc?
Maybe do a static pressure test of the cooling system with the spark plugs out, and scope the cylinders to see if you can find coolant drips. May need to rotate the engine to observe the entire wall in each cylinder.
Wait. I do have coolant in the oil. I stuck a borescope into each cylinder and no coolant/water. I'll take some pictures in the morning.
 
My apologies for not stating it clearly; oil in radiator and coolant in oil.
 
cracked/warped head causes oil/water mixing. Common on these. overheat lately? Mine "ran fine" too (at purchase) until summertime hills came calling.
You were right. Cracked head on top between cylinders 4 and 5 exhaust side.

20250201_122950.jpg
 
As an observation from outside, you have stayed in a couple cases "that's not the problem".

I'm not meaning to gouge, but step back a minute and rethink every test you've done. Take nothing for granted.

You have oil in the coolant.
You do not have coolant in the oil.
You are losing coolant.

Where can oil get into the coolant, but coolant cannot get back into the oil?
The oil must be at higher pressure than the coolant.

Where am I losing coolant?

I hate to say it, but I think you may have a cracked cylinder wall. That's why you need to do an exhaust gases test in the coolant.

After you did the oil cooler clean and reseal, how did you flush and clean the cooling system to get the oil out of the radiator, block, heater cores, etc?
Maybe do a static pressure test of the cooling system with the spark plugs out, and scope the cylinders to see if you can find coolant drips. May need to rotate the engine to observe the entire wall in each cylinder.
Thanks for the pressurizing idea. The cylinder walls were ok. I found a crack on the head.
 
I see water but where's the crack??

Did you suspect anything wrong with the head while it was apart? Installed a new head or rebuilt original head?
 
You were right. Cracked head on top between cylinders 4 and 5 exhaust side.

View attachment 3829379
Is it leaking below the cylinder head plug? You can replace the metal gasket under each one of those big Allen heads. The gaskets come in the engine gasket kit.
 

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