Oil in coolant expansion tank

[67GTA]

Looking for a sanity check here before I pull the engine for tear down and inspection. For the last couple events, I’ve had trace amounts of oil in the coolant expansion tank. Not a lot of oil - just enough to form a nasty colored line around the edge of the tank, but it’s definitely oil. The cooling system seems to be over-pressurizing as well and will burp coolant out the cap when pushed for more than a couple laps. Temperatures are good - nothing over 205 or so at the point the system would push coolant out the cap. Engine oil is clean from what I can tell - no milky white filler cap, dipstick is clean and clear. And the thing is running as strong as it ever has - absolutely no performance concerns.

My initial suspect is a cylinder head gasket, but want to see if there’s anywhere else on these engines that could cross-contaminate that perhaps I’m missing? I’m using the Ford Performance oil cooler adapter on the block for a remote mount filter and cooler ruling out that possibility.

This is a Gen3 block with GT500 oil pump, which makes a LOT of oil pressure. Gen1 heads, which have a smaller oil passage through the head gasket than the later gen heads. Could the high pressure with smaller passage have compromised the head gasket??

I really don’t want to pull the engine right now with the thing running so well, but don’t want to cause bigger issues by not addressing it.

 

[mwjscn]

One of the potential symptoms of a head gasket failure is pressurization of the water circuit due to it now being exposed to cylinder pressure (would fit why temperatures are fine but it's puking anyways). When it's idling, do you see any bubbling in the coolant reservoir (leaking cylinder compression) or any steam coming from the exhaust (consuming coolant)? Sometimes when something is so minor it's really hard to track down or see any other symptoms.
You may also be able to run a compression test before pulling the engine and see if a cylinder or a couple cylinders are noticeably down compared to the rest, since the path of least resistance would be for the pressure to escape through the potential break in the gasket. A leak-down style tester would probably be best for this.
With the spark plugs removed, you can also pressurize the coolant system and engage the starter (disengage the fuel system) to see if any coolant is thrown out of the spark plug holes or is otherwise getting in the cylinder.
If you don't have these tools but have an air compressor, you can usually rent them from your local Autozone or Advance Auto.

Edit: I did just ask the Ford Performance chat if there were any concerns using the Gen 1 headgasket with the smaller VCT provision in combination with the 2020+ GT500 oil pump and the line supervisor doubted it could cause a problem, though they suggested reaching out to [email protected] if you had any further concerns or points you wanted to talk about. As someone who wanted to do this as well with a Gen 1, please share if you do find anything problematic regarding that pairing.

 

[Dave_W]

Haven't had the need to use it myself, but I wonder if a kit like this would help diagnose.

75500 Combustion Leak Detector

Quickly Pinpoints Combustion Leaks.

www.lislecorp.com

 

[2012-Boss]

Did you replace the overflow cap? It is one time use. It has to be replaced every time it springs. Is the oil slime getting worse, or staying the same?

 

[67GTA]

Did you replace the overflow cap? It is one time use. It has to be replaced every time it springs. Is the oil slime getting worse, or staying the same?

I didn’t realize the caps were one-time use. The cap was new about a month ago but has now purged a few times. The amount of oil in the expansion tank is staying about the same.

 

[mwjscn]

The amount of oil in the expansion tank is staying about the same.

If it's a fresh build, is there any chance that the small amount of residual oil was from the engine assembly process?

 

[67GTA]

If it's a fresh build, is there any chance that the small amount of residual oil was from the engine assembly process?

The new engine has been in for just over a year and 18 or so track days before the issue.

 

[2012-Boss]

Change the cap an monitor. There is typically some sort of crap floating around my purge tank everytime I drain the system - which is usually at least once a year.

 

[67GTA]

Haven't had the need to use it myself, but I wonder if a kit like this would help diagnose.

75500 Combustion Leak Detector

Quickly Pinpoints Combustion Leaks.

www.lislecorp.com

If the fluid stays blue, no combustion leaks present. If the fluid turns yellow, lots of work ahead…..

 

[EF1]

Unfortunately, it looks like you have have a lot of work ahead of you.

 

[67GTA]

Pulled the engine this last weekend and tore down to the short block. Nothing unusual with the head studs and all were tight. I can’t see any obvious signs of a gasket breach on the head gaskets or sealing surfaces with my untrained eyes. I’ll post some pics later this week to see if the quorum sees something different.

One interesting thing that I discovered. The small hose that connects the expansion tank to the top left side of the radiator was plugged tight. At first I suspected a check valve, but it wouldn’t flow air in either direction. There’s a steel clamp a few inches from one end, and it felt like it was holding something inside the hose. Cut it open to inspect, and sure enough there’s a small brass check valve in there. Lots of corrosion and the ball was gummed up tight. Pushed it free with a small pick, allowing it to function properly. Now it has me wondering how much this clogged hose played in causing the cooling issues that led to the cross-contamination. Simple enough to check function, but not something I would have ever considered inspecting.

 

[SMGDHG]

Pulled the engine this last weekend and tore down to the short block. Nothing unusual with the head studs and all were tight. I can’t see any obvious signs of a gasket breach on the head gaskets or sealing surfaces with my untrained eyes. I’ll post some pics later this week to see if the quorum sees something different.

One interesting thing that I discovered. The small hose that connects the expansion tank to the top left side of the radiator was plugged tight. At first I suspected a check valve, but it wouldn’t flow air in either direction. There’s a steel clamp a few inches from one end, and it felt like it was holding something inside the hose. Cut it open to inspect, and sure enough there’s a small brass check valve in there. Lots of corrosion and the ball was gummed up tight. Pushed it free with a small pick, allowing it to function properly. Now it has me wondering how much this clogged hose played in causing the cooling issues that led to the cross-contamination. Simple enough to check function, but not something I would have ever considered inspecting.

View attachment 86068

You are thinking the failure of this check valve would result in over-pressurization of the cooling system? It is a good find but I am running through scenarios and it seems unlikely this could be the root cause of combustion gases making their way into your coolant.

Is the designed check valve flow path EXP TANK -> RAD or RAD -> EXP TANK ?

 

[mwjscn]

It looks like the radiator top vent line to the expansion tank to me, part BR3Z-8075-B, that runs from the top driver-side radiator nipple to the top nipple on the reservoir closest to the front of the car. If the vent line was plugged and not allowing pressure to release itself from the system, it could very well contribute towards the over pressurization and the rad cap bypassing. What's interesting though is that the radiator cap isn't physically on the radiator, but on the expansion tank (after the plugged check valve, not before). Perhaps the pressure was beating back towards the engine through the upper rad hose and exiting out the steam nipple on the water neck to the other top-mounted expansion tank nipple instead? Given all of that, I still don't know how that would lead to oil in the coolant.

 

[67GTA]

is a good find but I am running through scenarios and it seems unlikely this could be the root cause of combustion gases making their way into your coolant.

Given all of that, I still don't know how that would lead to oil in the coolant.

I’m not thinking this hose is directly tied to the combustion/oil cross contamination. There’s only a couple places in the entire system where oil pressure is higher than coolant - that’s at the cylinder head gaskets. The car overheated last August at Auto Club speedway. 100 degree ambient and went into limp mode, code P1299 “Cylinder Head Overtempurature Protection Active”. Coolant level was low. I had a Radium expansion tank at the time with a traditional style radiator cap and a relief hose that vented to atmosphere. After this event, I added a secondary catch can and confirmed the system was pushing coolant past the cap on warmer days. So, I believe the longer term effect of the cooling system not operating properly led to eventual head gasket failure or cracked head (still not sure which, but the failure has to be here).

What’s interesting on the bypass hose - the diagram that @mwjscn posted above shows the flow from radiator to expansion, however the check valve is designed to flow opposite of that.

 

[67GTA]

Finally had a chance tonight to inspect the short block. No longer a mystery where the combustion leak/cross contamination is coming from. Cylinder #8 with a crack in the sleeve. Looking at the gasket in this exact area I can clearly see where the breach is. Absolute gut punch.

 

[Hye Power]

All that nitrous you were shooting in there, j/k. That sucks man car was running amazing too, hate to see this.

 

[mwjscn]

Cylinder #8 with a crack in the sleeve.

They say it usually feels good to solve a mystery... but not sure about this time.

Do you still have a receipt for your shortblock? If I have my information correct, in your build thread you said that you ordered it December 2nd 2021. That would still put you within the Ford Parts Warranty period. The attached document says it excludes racing, but honestly this failure seems a little out of left field on such a new engine, so it depends on how well the parts vendor you got it from knows you or their general willingness to help.

 

[67GTA]

They say it usually feels good to solve a mystery... but not sure about this time.

Do you still have a receipt for your shortblock? If I have my information correct, in your build thread you said that you ordered it December 2nd 2021. That would still put you within the Ford Parts Warranty period. The attached document says it excludes racing, but honestly this failure seems a little out of left field on such a new engine, so it depends on how well the parts vendor you got it from knows you or their general willingness to help.

That’s correct on the original purchase date. The shortblock was built by RPG Race Engines and came with a 6 month warranty. After piecing everything together, neither Ford Performance nor RPG should warranty the cracked block. I don’t think I mentioned it earlier in this thread, but after removing the intake manifold I noticed a plastic tab from the engine wiring harness was pinched between the manifold and the cylinder head. If that tab was required to be installed that way, there’s no way I could ever get it to line up. But with amazing luck, the damn thing was perfectly inline with the manifold gasket. You can even see the line where the gasket indented the tab, I’m sure after a few heat cycles. I assume just enough vacuum leak to run lean on that cylinder at higher RPM’s, but not enough to cause rough idle, etc. And of course it’s cylinder #8.

So here’s my final reasoning on the failure;

- compromised intake manifold gasket in Cylinder 8 causing lean conditions and additional heat

- plugged hose from expansion tank to radiator would force coolant to bypass the radiator cap on the Radium expansion tank (which I believe is too small for this system) during combo of high ambient temperatures and above mentioned lean condition

-eventual low coolant level from tank purge, leading to cylinder overheat condition and damage to cylinder sleeve.

This is the only sense I can make of this whole mess, but onward we go. New Ford Performance Gen3 block was delivered today, so I’ll be swapping the rotating assembly over with fresh rings and bearings. Follow along in my build thread for updates on 406 v3!

 

[Tri-bar]

Glad you have a plan and should be back soon.

 

[misterpeanut]

What a super unfortunate series of events.