Oil film in coolant reservoir

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sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Oil film in coolant reservoir

Post by sgnimj96 »

Went on a 800mile trip. Getting ready to returned, noticed oily film floating in the coolant reservoir,
Cleaned out the reservoir and headed back. Oil film formed again in the reservoir, had to add a little coolant a couple times
to keep it up to level, but ran fine. No coolant in the engine oil.
After I got back I cleaned out the oil film again, but it kept coming back.
I had changed that head gasket well before the trip using the upgrade of head studs. The old HG with the hex bolts looked terrible.
The studs on the new HG were plenty tight. Retorqued to 90lbs after I got back to see if that would keep the oil from sneaking into the coolant. Nope
So I put some air pressure into the reservoir nipple with a hand pump and.... coolant started coming out at the head gasket around #3 cyl area.
I pulled the head and the gasket looked ok, but I don't know much about head gaskets.
I'm going to get the head checked at a machine shop, but
This is one of those 11mm engines that people say get cracks in the block.
Dang. It may be toast
Maybe I just didn't prep the surfaces good enough, I did use hylomar spray.
Long distance ruising at 75 is kinda hard those old engines, sometimes pushing it over 80.
I do have a rockauto Goetze HG standing by to try. The last HG was a cheapo from Hansauto
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Re: Oil film in coolant reservoir

Post by Fatmobile »

Check your coolant reservoir cap/cooling system pressure.

There is only one place on the gasket or cracked block where oil has enough pressure to push itself into the coolant.

Don't tighten cap when you restart it.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

Thanks for the insight Fatmobile
I just tested the cap I was using, It was new (cheap URO) and it FAILED
When I pressured the entire cooling system, it only went to 20psi but started blowing coolant out of the HG.
When I tested the cap by itself... I stopped pumping after 35psi
Image
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

machine shop man gave it look,
not warped but that head is marked as having been resurfaced .015"
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Re: Oil film in coolant reservoir

Post by Fatmobile »

So you lost a head gasket because of a coolant reservoir cap too?

Before my experience I always thought they would fail low and let coolant out.

I had very stiff top rad hose, it should be someone easy to crush.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

I thought my old cap was leaking. Did a pressure test on the system through the reservoir nipple
with the hand pump, the old cap released at ~15 psi.
So I just put a new cap on and thought that had to be a good thing,
I never tested the new URO cap.

I read that testing at higher pressures than 25 can blow out a gasket.
Thing is, it was losing a bit of coolant before I changed the cap.
so whatever that problem was, the new URO stuck cap just made it worse.
I think the system was slowly venting out of the HG on my trip.
It just kept getting worse, but I made it without any real issues maybe because that engine was
running extra cool most of the time.
Many people would have not even noticed, but like I said.
when I eventually pressure tested the whole system again,
I spewed out coolant from the front of the HG at ~20psi :shock:
Last edited by sgnimj96 on Mon Jan 31, 2022 9:22 am, edited 1 time in total.
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Re: Oil film in coolant reservoir

Post by Fatmobile »

I'm starting to wonder if the reservoir cap is responsible for more blown head gaskets than we realize.
Might need to install a cooling system pressure switch/warning light.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
scrounger
Glow Plug
Posts: 17
Joined: Sat Feb 09, 2013 6:47 pm

Re: Oil film in coolant reservoir

Post by scrounger »

Do you think that the 15psi cap. is going add significant pressure when compared to the combustion chamber pressure? Even cranking pressure is what, 350psi Running pressure has to be significantly higher than that.

Seems to me that an unpressurized cooling system would actually add another 15psi to the pressure gradient between the sides of the combustion chamber side and the cooling ports of the head gasket.

Maybe I am wrong?
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

I've been fixing my cars for most of my life but really don't know much about engine building
or the actual thermal dynamics going on.
If I have done a better job on the head gasket the problem of the faulty rad cap probably wouldn't have shown itself so quickly.

I was reading this article about rad cap problems https://intrepidoverland.com/bad-coolan ... ad-gasket/
And someone added a comment that (early?) VW radiator caps ARE problematic
"As soon as the liquid cooled Rabbits, Jettas, etc started coming in we had problems with the cooling system caps.
We got a Stant pressure tester and the VW adapter. We would order up 10 caps at a time and test them all as there were so many problems.
Half or more would fail. Would not hold pressure or relief was too high(over 20 psi) or the return/low pressure part was bad.
These (caps) were mostly from the VW dealer. After we got the tester and rejected the out of spec caps there were almost 0 problems."
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

Fatmobile wrote: Sun Jan 30, 2022 12:05 am I'm starting to wonder if the reservoir cap is responsible for more blown head gaskets than we realize.
Might need to install a cooling system pressure switch/warning light.
I suppose if the glowplug temp sensor isn't used (pimped system), something could be put there from a gauge.
VW does have the high pressure oil sensor that screws into the oil filter housing (22-29psi?) but it's normally-closed
so that's backwards for a high pressure indicator.
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Re: Oil film in coolant reservoir

Post by Fatmobile »

scrounger wrote: Sun Jan 30, 2022 7:24 pm Do you think that the 15psi cap. is going add significant pressure when compared to the combustion chamber pressure? Even cranking pressure is what, 350psi Running pressure has to be significantly higher than that.

Seems to me that an unpressurized cooling system would actually add another 15psi to the pressure gradient between the sides of the combustion chamber side and the cooling ports of the head gasket.

Maybe I am wrong?
When I had the problem I could hear the head boiling.
Even though the engine wasn't overheating.
So local pressure in the head could be much higher than 20.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

the head gasket I ordered from RockAuto was one of those felpro closeouts,
but the actual gasket was a NOS Goetze, pretty cool.
This time I hit the block with wd40 and 150grit using square of flat marble tile as a sanding block.
To keep grit out of the bores I smeared grease on the pistons and sticking toilet paper to that.
The head got cleaned up pretty good by the machine shop guy using a plastic roloc.
So I got the head on (hylomar spray), ran it, degreased the cooling system again (and again), changed the oil.
Last edited by sgnimj96 on Thu Feb 03, 2022 11:01 pm, edited 1 time in total.
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

Drove around for a while then wanted to test the reservoir for combustion gases.
Rigged up cheesy tester using bong technology
Image
Bought the test fluid from HF for $10
Image
Put just a small about of the blue test fluid in the bottle and
used a mityvac to pull air through the top tube.
Overflow wasn't pressuring, good sign, but made it a little harder to pull air.
Sure enough the bubbles going through the fluid didn't change the color at all. Good sign. (even put the used fluid back)
Then I wanted to go over the radiator caps I had again
The old oem green cap vented out at a nice at 14psi, BUT would hold a bit of
vaccum when it vented in. (They vent in when the system cools down after shutoff)
I remember noticing that when opening the cap (cold) sometimes it had a slight vaccum
on it. I assume this is a fail of the cap!
Tested it with a mityvac and verifed that it was holding a slight vaccum
Image
Tested the motorad cap that vents at 18 psi and it held no vaccum so I'm using that one.
Tested the 25psi URO cap and it HELD vaccum at 4-5psi, even worse.
Image
Might not seem like a big deal but it can't be a good thing for the cooling system to sit like that.
I imagine sitting under a slight vaccum while the engine cools down and them perhaps for hours (or more)
after that would stress out seals and the cap itself.

So, to recap, lol
I had 4 rad caps: 2 new URO, 1 new motorad, and 1 old green oem
All failed (IMO) except the Motorad T25 cap.
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

Then I tested my thermostat on the stove in a pot of water, because it was running too cool.
Out of 4 thermostats only 1 worked to my satisfaction. One was a stant superstat stuck closed way too long :x .
Then I took it for a longer drive and sure enough it ran at the proper steady 190,
and finally took it on the freeway for some miles at solid speeds.

But even after 2 degreasings of the system, there is still a slight little film of oil in the edges
of the reservoir after it cools down, but much less significant.
Maybe I should have used something better than dollar store dishwasher detergent.
So a bit of residue is still in there, but it looks much better than before.
I'll just keep an eye on it and hope there isnt' some hidden micro-crack in that
old 11mm block.
Gotta say, these coolant flushes are getting old.
Good thing I recently filtered some rain water and have that to use.
I even got some of that radiator anti-rust stuff to add to the antifreeze so I can
use less of that until this gets sorted.

The most interesting thing to me is - how the radiator caps and thermostats can be so
quietly problematic, especially with aftermarket ones,
They rarely get checked and often tip the scales to ruining good engines.
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
sgnimj96
Turbo Charger
Posts: 259
Joined: Thu Feb 20, 2014 2:08 pm

Re: Oil film in coolant reservoir

Post by sgnimj96 »

Well, after all that wishful thinking the engine is still leaking oil into the coolant.
It got worse after some moderate driving. Still runs nice,
but I don't know how to fix this problem.
I need to get another engine to swap in.
81' Scirocco 1.6D (conversion)
86 Golf 1.6D
85' 300TD
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