hjb981

Oil in coolant tank (Northstar)

15 posts in this topic

This question is about a 1997 Cadillac DeVille with the 275 Hp version of the Northstar engine.

As part of my regular inspection routine, I checked the coolant a few days ago, and it looked somewhat strange. Today, with a 200-mile trip since I first noticed the strange look of the coolant, i checked it again, and it looks like there is oil in the coolant. Not very much, but just a few drops visible in the surge tank, and a some traces of it on the plastic tab/ridge that sits right under the surge tank cap.

- The coolant level has not changed, and the engine oil looks normal (light brown and clear).

- The transmission fluid was clear and red.

- All fluids smelled like they usually do.

- The coolant system pressurizes like normal, and holds pressure like normal.

- I check these things every now and then, so I have a pretty good idea of the normal state of things.

Checking my radiator, I found that:

- On the passenger's side, there are two unused connections in the side tank.

- On the driver's side, there are two connections in the side tank that have narrow steel tubes going out of them. I could not see where they went from there.

- In front of the radiator (and AC radiator) there was a small steel radiator comprising a steel tube that was bent twice (so as to form three parallel lines) and cooling fins (also steel) that were attached to the three parallel lines of steel tubing. I have not found any information on what this is, and I could not see where the lines went.

In the 1997 FSM, I found the following conflicting information:

Page 6-193, under Radiator Replacement:

8. Disconnect the engine oil cooler lines

from the right radiator end tank.

9. Disconnect the transmission oil cooler lines

from the left radiator end tank.

Page 6-197, under Radiator Assembly:

"... The right side end tank houses the transmission oil cooler. The let side end tank houses the engine oil cooler. ..."

This was accompanied by a numbered illustration, which denoted the end tank cooler on the side with the drain plug, which is the driver's side, as the engine oil cooler, and the end tank cooler on the other side (passenger's side) as the transmission oil cooler (consistent with the text on the same page, but in conflict with the text on page 193).

Some additional information:

- I change my coolant with two-year intervals, with the last change almost two years ago (I plan on changing it by the end of summer). I always use DexCool plus deionized water and add two GM sealant tabs after draining the system (since I only drain and refill without flushing, some of the old coolant stays, hence only two pellets and the biannual change interval).

- The engine operating temperature during my last 300 miles of driving (as well as the 80000 miles that I have driven before that) was normal (about 196 F when cruising, rising a bit when going from highway to city driving and falling a few degrees during WOT (I guess as a result of the increased coolant flow at the higher RPM)).

- It is currently warm were I live, about 80 F, so the AC is running, but I have always seen the same engine temperature behavior whether it is 80 or -10 F outside. Always about 196 F when cruising, going up a bit when going from highway to city and going down a few degrees after WOT (has been the same for the nine years I have had the car).

Some questions:

- Do I have a transmission or engine oil cooler in my driver's side radiator end tank?

- What is the small and simple cooler that sits in front of my radiator?

- What could be possible causes for the oil in the coolant?

- Is there a possibility that there is also coolant in the oil, but since coolant is heavier than oil, it sits at the bottom of the oil pan without causing any visible signs on the dipstick or under the oil filling cap? I guess that the oil pick up does not sit right at the very bottom of the pan, but slightly above it. I am asking this because if oil is pushed into the coolant system when the engine is on, coolant might be pushed in the other direction when the engine is switched off, since the cooling system remains pressurized for a while, while the oiling system looses pressure immediately when the engine is not running.

Thanks in advance,

Jonas

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....

Some questions:

- Do I have a transmission or engine oil cooler in my driver's side radiator end tank?

Yes. Driver's side is transmission cooler.

- What is the small and simple cooler that sits in front of my radiator?

Power steering fluid cooler.

- What could be possible causes for the oil in the coolant?

No idea. Is it sure enough oil?

- Is there a possibility that there is also coolant in the oil, but since coolant is heavier than oil, it sits at the bottom of the oil pan without causing any visible signs on the dipstick or under the oil filling cap? I guess that the oil pick up does not sit right at the very bottom of the pan, but slightly above it. I am asking this because if oil is pushed into the coolant system when the engine is on, coolant might be pushed in the other direction when the engine is switched off, since the cooling system remains pressurized for a while, while the oiling system looses pressure immediately when the engine is not running.

Too speculative.


Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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No idea. Is it sure enough oil?

Something that does not mix properly with the coolant, even after 200 miles of driving, so I would say that it is likely oil. The part that was on the "plastic tab" under the coolant reservoir cap also looked like engine oil, although hard to be absolutely sure due to the small amount. I will try to take some pictures of it tomorrow (it is dark here at the moment). When wiping the coolant reservoir neck, there was some stuff there that looked more like used oil or grease (black rather than the brown color of my engine oil (I have never left oil in the engine long enough for it to turn that black)). Maybe the black stuff originated from the gasket of the cap, though, and it was only present right there in the neck of the reservoir.

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Just in case....The coolant tabs can make the tanks look like there is oil in them. The tanks never look nice and clean like other cars.

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The 275 hp Northstar does not have an engine oil cooler, which would be in the right (passenger side) radiator tank. A leaking oil cooler is the only credible path from oil to the coolant. Except for an idiot in a filling station that can't tell the difference between a coolant tank cap and an oil filler cap.

Yes, I see page 6-197 with its exploded diagram of a radiator, and it names the numbered pieces in the diagram so that it places the oil cooler on the left and the transmission fluid cooler on the right. However, I think that's a rare error in the FSM. Check Radiator Replacement on pages 6-193 through 6-195. There, step 8 says "Disconnect the engine oil cooler lines from the right radiator end tank." Step 9 says "Disconnect the transmission oil cooler lines from the left radiator oil tank." Also note that the transmission is on the left side of the engine/transmission assembly.

There is always a transmission fluid cooler on the left (driver's side) radiator tank. The oil you see in the surge tank might be transmission fluid. If so, you need to deal with it ASAP because coolant in the transmission means a full tear-down and rebuild of the transmission.


CTS-V_Dashboard.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Below are two pictures of the coolant in my reservoir, with focus on the plastic tab in the first picture, and focus on the coolant in the second picture.

IMGP1893.JPG

Large version: https://lh4.googleusercontent.com/-DnV82I9bpYk/UgDwVRu2zII/AAAAAAAAATg/0JaEkccDQRE/s1600/IMGP1893.JPG

Picture 1. The light-brown, turbid residue on the plastic tab has always been there, and I think it originates from the sealant tabs. The somewhat darker, clear stuff, on the other hand, has not been there before. It looks like engine oil to me (the color is very similar to the 10W-30 in my engine that I changed fairly recently (OLM says 88% left)). My ATF was last changed a few years ago, and has the same red color as new ATF.

IMGP1898.JPG

Large version: https://lh3.googleusercontent.com/-h13oUmKoEnc/UgDweG0-bfI/AAAAAAAAATo/STAaSBveQrI/s1600/IMGP1898.JPG

Picture 2. There is some stuff floating on top of the coolant as well.

What do you think of the looks of these pictures?

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I think you should get a pressure test on the radiator ASAP. If it turns out to be the transmission cooler, you may save the transmission. Whatever it is, you will find it either in a radiator pressure test or, if the radiator is good or with a new radiator, in a cooling system pressure test.

It looks like transmission fluid to me.


CTS-V_Dashboard.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I started the car today with the coolant surge tank cap off, and after a while, the coolant started rising (like it always does due to thermal expansion). If I revved the engine, the coolant would go back a bit, due to the pump pressurizing the system (could be felt on the radiator hose, again with the cap off). When I let off the gas, the coolant would flow back into the surge tank again.

When hitting the gas, I could see a fine mist over the surface of the coolant, and as the engine got even warmer, I could see tiny bubbles (similar to simmering water). When smelling it, I think it smelled very much like coolant and not like exhaust. I was thinking that maybe the very fine mist (only visible when shining with a flashlight directly over the coolant) could be due to increased coolant flow at higher pump speeds, and that the bubbles were actually simmering.

After the engine was warmed up, I put the cap back on and drove a few miles. The coolant system did not build up much pressure when doing this (the upper radiator hose was still soft). After driving several miles more, including some cycles of fast driving followed by city driving and idling (which had the temp increase to 215 F at the most) there was some pressure, but still less than normal (when the cap would have been on from ambient temperature, allowing for greater pressure build-up due to thermal expansion).

IMGP1902.JPG

Large: https://lh5.googleusercontent.com/-gzdpaXMNRm4/UgElxl_1UsI/AAAAAAAAAT8/BKMo1tVP3-Y/s1600/IMGP1902.JPG

Picture 3. The transmission fluid looks normal.

IMGP1904.JPG

Large: https://lh5.googleusercontent.com/-LT89pN4qusw/UgEl2AtPSdI/AAAAAAAAAUE/J9s_yUVbjsc/s1600/IMGP1904.JPG

Picture 4. The dark stuff in the lower right part of the image was wiped off of the coolant surge tank neck. The pieces of paper in the upper part of the image were dipped into the coolant tank. The oil can be seen as something dark together with the light red of the DexCool.

IMGP1907.JPG

Large: https://lh3.googleusercontent.com/-nho0N-XckRc/UgEl6LFV36I/AAAAAAAAAUM/TYsFahhh8gM/s1600/IMGP1907.JPG

Picture 5a. Small bubbles in the surge tank with warm engine (radiator cap was off during the warmup phase.

IMGP1908.JPG

Large: https://lh4.googleusercontent.com/-QCNGlvyIpWo/UgEl_XjlP-I/AAAAAAAAAUU/CLiEqYnbMJ8/s1600/IMGP1908.JPG

Picture 5b. Another depiction of the same thing as in picture 5a. Notice the small black piece of something in the coolant. There were more of those (see also Picture 5a).

What would you make of this?

Cadillac Jim: how do you pressure test the radiator, can it be done without removing it?

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The pressure tester installs on the surge tank (in place of the radiator). It's a little pump - similar to a basketball pump with a check valve and a pressure gage. After installing the pressure tester, pump it up to the pressure rating stated on the cap and see if it holds pressure. If it does not, look for the leak. The nice part is that the system can be pressure tested with the engine cold so you can inspect for leaks better and not risk getting burned by a hot engine.

Since you have what may appear as engine oil in the coolant, a place to start would be the oil cooler in the trans tank (assuming your car has one). Very easy to tell - the transmission lines are at one end of the radiator and the oil cooler lines (if your car is equipped) will be in the opposite side tank.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I DO have a transmission fluid cooler on the left side of my radiator.

I DO NOT have an engine oil cooler (even if there is one present on the right side of the radiator, it is not connected, there are just to plugged holes).

Thanks for the input!

If I find that there is a system leak in a pressure test, how do I find out where it is? Since this should be an internal leak (between the coolant circuit and an oil or ATF circuit) it would not be very obvious where the leak was. Any ideas on that? Maybe it is less expensive to simply replace the radiator than to try to confirm a leak between the coolant and ATF circuits (leak in the ATF cooling circuit)?

I ran the car to operating temperature again today, this time with a little less coolant in the surge tank but with the cap on. When I was checking things yesterday with the cap off, some coolant overflowed when the engine got warm. The pressure (measured by squeezing the upper radiator hose with my hand) was a little lower than normal, which is exactly what I would expect since there was a little bit more (compressible) air in the system. I did this check because I suspected the bubbles to be exhaust gases, but if they were they should have pressurized the system just as much also with a small amount of extra air in it. I am confused; are those bubbles normal?

There was also a bigger (almost a quarter inch) black piece of something in the coolant today before I started the engine (after yesterdays tests, I had to wait until the system was cool today to check). I fished it out of the tank, and looked like grease (used, black grease) and had the same consistency as grease. That black stuff did not look like engine oil and also not like ATF. Even if there is a leak, I do not understand what is going on here... There are no pressurized systems from which black greasy stuff could leak into the coolant... Could it have formed from deteriorating hoses that mixed with oil...??? Could it be a mixture of oil or ATF and coolant?

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The oil or ATF will not mix with the coolant in the surge tank.

I would suspect that it is a small piece of the inside of a hose.

Over time, they will begin to break down and get gummy...

Have you tried to stick a piece of paper towel down into the surge tank and touch some of the suspected oil / ATF spots??

The paper towel would absorb them and that may tell you something about what it is.


Posted Image

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Picture 4 a few posts up shows paper towels that were dipped in the surge tank (the ones at the top). The paper towels in the top of the picture do not show the black stuff, just the oily stuff floating around in there together with coolant. Picture 4 also shows some of that greasy stuff smeared out (the black stuff on the paper in the bottom of the picture). The greasy stuff that I managed to pick out of the tank has been drying on a piece of paper towel over night, and it looks like the paper towel has wicked out oil from it (brown like engine oil). The greasy stuff also looks drier. I think it is just something like deteriorated hose that has formed this together with oil.

I other words, the only question now is why there is oil in my coolant system. One possibility is the transmission cooler. The only other place I can think of where coolant and oil could mix is the engine.

I guess that both the oil and ATF pressures could reach levels above the cooling system pressure, and with a very small leak, it might explain why I only see contamination in one direction (to the cooling system).

Cadillac Jim mentioned (and I think I have seen others mention it as well) that the Northstar is design so that leakage between the oil and coolant passages is very unlikely. Why is that? There must be some places where both oil and coolant pass the same gasket, such as between the block and the heads. Are the passages spaced far apart, or what makes leakage between them unlikely?

Edited by hjb981

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I would not just replace the radiator in hope that it will fix the problem. It would be expensive and a lot of work just to be disappointed.

The pressure check will tell you if the system is leaking. It will be difficult to see where it is leaking if it is internal. It could be just the inside of a hose breaking down and the crud in the tank looks like oil.

Coolant WILL leak into the oil if the head gaskets are shot. I had that on the '97 STS I bought to fix up several years back. I do not recall any oil in the coolant though.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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My complete honest opinion

To me it looks like bars leak and a small amount of sludge. When was the last time the coolant was changed? you could also pull a sample and get it analyzed.

with you having the oil cooler in your non equipped car tells me it has been replaced. Gm and aftermarket stopped production of the units without both coolers awhile back and only offer 1 radiator which has both the oil and trans cooler. But if it still had the original it would not have the oil cooler ports


GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Thanks, I am hoping that it is just something that I missed, and simply some sludge or something else that is harmless.

The last coolant change was almost two years ago (drain, add two sealant tabs to lower radiator hose, fill with 50% dexcool + 50% deionized water). I change every two years, so it is time to change again about now.

I check the coolant (by looking in the surge tank) at least once a month to make sure all is well, and I have not seen this before.

Interesting to know that the radiator has been replaced, but that must have been over nine years ago, since I have not raplaced it.

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