Oil or Transmission Fluid in Coolant?

2001 Malibu, 3100 SFI, 80K miles, maintenance regularly
I have a fluid in the coolant reservoir that’s oily but I don’t know whether it is oil or transmission fluid. What methods can I use to determine whether it is oil or tranny fluid? The amount of fluid appears to be only 3-4 teaspoon.
The car has no issue and has never been overheated. The lower intake manifold does leak coolant to the driver side and probably the passenger side of the engine also. This leak has been so minimal I’ve only had to add coolant 4 times, a pint or 2 each time, since I bought it new in 2001.
Oil changes 3k interval, coolant flush and fill at 60K in 2006, tranny fluid & filter replaced 70K in 2007. The tranny fluid had light sediment on pan but I assume was normal clutch wear. The tranny fluid had no indication coolant that I could see. I was just checking to see if the spark plug would really go 100K and checked the plug in the middle closest to the radiator and there was no indication of gap wear or fouling of any kind.
Side question, is there a way to post pic to this site? It sure would be helpful.

Is your coolant the Dextra-Cool (orange color)? This coolant will gel up when exposed to air such as a leak. You might just remove the coolant bottle and do a good cleaning, and keep monitoring it. Permanent option is to replace the intake gasket, $55 @ Murray Discount, and 6-8 hours of top end work. Just completed my 99 Malibu, not that bad of a job.

Thanks gjhunter01 for the input. I’m glad to hear you didn’t think replacing the lower intake manifold(LIM) was that bad. I’m trying to postpone replacing the LIM as long as possible. But right now I’m trying to diagnose if I have a bad radiator leaking transmission fluid into the coolant system, a LIM that’s leaking oil into the coolant or an omen of a bad head gasket leaking oil into the coolant system. I guess a compression test on the cylinders might give me a clue but the leak is so small I don’t think the compression test will show anything.
Anybody else have some more ideas?

Micosan - my coolant had Transmission Fluid in it, when I thought it was oil. Better check it out. I couldn't tell the difference. I ended up having a radiator leak into the transmission.

100% guarantee you have a bad intake gasket. The oil mix and coolant on the block are the symptoms. The leak will only get worse to the point that you either fix the problem or ruin the engine. Sounds like it just started to leak so you may be OK for a bit but I wouldn't push my luck. Your coolant will eventually be black and your oil will tan. Put it this way oil does not cool down an engine and antifreeze does not lubricate.

My only previous automotive skills were related to oil, coolant and brake liner replacements.

Last week I looked at the oil cap and saw about a quarter inch of the dreaded butter-scotch whip cream of oil and coolant mix. I was hoping I had dodged the trouble of the leaking LIM. After removing the LIM there wasn’t any obvious sign to me of where the gasket failed. Although there was a build up of a cream mixture of oil and coolant in the left valve cover closest to the radiator. There was no cream build up on the other valve cover. There was a sticky coolant film in the number 5 & 6 cylinder exhaust rods and grooves. There were external leaks around cylinder 1 & 2 but appeared to be mostly external.

I guess I’m lucky I didn’t postpone replacing the LIM gasket any further since there doesn’t appear to be any significant amount of coolant in the engine or oil lessening the possibilities of damage to any bearings.
The job took me significantly longer than others who have posted here. I’m guessing it took me about 25 hours. For me it was a steep learning curve just to remove all the electrical connectors and wiring clips. I also spent 4 to 6 hours just cleaning things including all the gaskets mating surfaces. Carbon buildup was significant in my opinion but then
I’ve never gone this deep into an engine. I spent some time taking picture and reviewing how each item work mechanically. I had never turned over an engine before by using a ratchet on the crank bolt and the resistance to turning the engine was more significant than I had anticipated. But this may have been due to the awkward position of the reach to access the crank bolt from the top of the engine with the combination of using a 10 inch ratchet. The plugs were removed when I turned the over the engine and my other ratchets were too big to fit in the small gap between the crank pulley and the car frame.

An unexpected issue I came across was the bolts for the engine lift brackets. There are three bolts holding the bracket and each bolt is different so someone may want to note this in case they’re in a similar situation. In my case the longest bolt went through the tensioner and bracket, the next longest bolt went toward the top and the shortest bolt went in the remaining hole if I remember correctly. The two shorter bolts at the top look very similar but if you hold the belt tensioner and the lift bracket together as the would be mounted on the engine, you can place the bolts in the two holes and look how far they would extend into the engine block. Both bolts should extend the same amount otherwise reverse the positions of the two bolts.

Here are some of my errors which costs me lots of time. I didn’t connect the ECT until after installing the upper intake manifold with throttle body attached. I didn’t connect the alternator wires before installing the power steering pump. I installed the radiator hose before installing the throttle body coolant line. I didn’t have any flare wrenches. I put the plugs in and forgot to coat with anti-seize and then removed them again to turn over the engine to verify all push rods were placed correctly. I misrouted the cam position sensor. I almost forgot to put in a bolt underneath the alternator for the alternator to engine block bracket. I installed the ignition coil packs 3 times because I forgot to install the valve cover fresh air intake tube and then I misrouted the plug wire bundle for 1, 3 and 5, the wires had to go under the fresh air intake tube. I forgot to attach the coil wires that came from under the engine until after installing the upper intake manifold. This wire also had a support clip which attached to the underside of the throttle body coolant bracket. I took the engine mount bracket off several times and then jacked the oil pan each time to support the engine. I jacked the car up and down several time to drain the fluids, forgot if I torque the drain plug enough and then again to replace the oil filter. I confined my work space and tools to my half the garage so the other car can be driven in and out. This is not a well lighted garage for repair purpose at night. I worked on the vehicle after work so it was difficult to see things.

I should have put a plastic bag over the fuel pump regulator to protect the filter from contamination. I forgot to clean the rods before laying down a very thin film of RTV around the coolant passage on the block and lower intake manifold and a thick bead in the valley area of the block mating with the lower intake manifold. So I felt the need to hurriedly clean the rods and installed them before the RTV setup. I don’t know why I was obsessed with cleaning the rods since I don’t know any advantages of clean push rods. In my haste I didn’t really get to take my time and visually check the short and long rods for each cylinder were placed correctly and seated properly in the lifters. Although a visual verification wasn’t necessary since I placed all the rods in a Styrofoam board marked for each cylinder. Anyway I really made an effort to turn the engine over by hand and verify all the rods were in the proper positions.

Things I replaced:
I would have replaced the o-ring on the oil pump drive shaft but the existing o-ring appeared to be in good condition and it was the light brown color o-ring which is suppose to be the new more resistance o-ring. The o-ring I had was a Fel-pro but it didn’t appeared to be anything special. I did add the distributor gasket to the top of the oil pump drive shaft for insurance.
I would have replaced the o-rings for the injectors but the o-rings I got didn’t appear to be the correct size. They were slight smaller in diameter and slightly thicker than what were on the injectors. I couldn’t install the new o-rings on the injectors so I left the existing o-rings alone.
I believe there is a o-ring on the heater pipe connected to the thermostat housing but since I didn’t see any notes of an o-ring there I wasn’t prepared to replace it so I wrapped some Teflon tape around what appeared to be an o-ring on the pipe and shoved it into the thermostat housing.

I did replace the thermostat, the o-ring on the thermostat bypass pipe at the water pump, the valve cover gaskets, spark plugs and wires, drive belt and of course the coolant, oil and filter.
The EGR valve gasket was in good shape. I only disconnected one side of the EGR valve so there was no need to replace the gasket on the other side of the EGR valve.

One of the things I was told to do was to rinse the engine valley, lifters and other areas under the lower intake manifold before assembly with transmission fluid. I did it but I don’t understand why transmission fluid and not motor oil. Maybe an experience tech could explain the reason for this.

The only way I was successful in reassembling all of the wiring and routing of all the things in the engine bay was by taking lots of pictures during the dismantling. I had no issues with starting the engine after assembly. It took two startup attempts of about 15-20 seconds each with a few minutes between attempts. The first startup attempt had no indication it would start. I verified fuel at the fuel rail and then tried a second start attempt. The second attempt had no indication of starting until after about 10 seconds and then there was some indication of ignition at which time I continued tuning the engine over.

The engine started with a very light tapping which I assumed were lifter noise. This light tapping went away in about 5 minutes except for a continue tapping on cylinder one which did finally end about 10 minutes later. After the engine had reached operating temperature I continue to have no heat from the heater until after I installed the coolant cap. While the car idled in the first 15 minutes I think it went through an idle relearned procedure. The car idled well after the initial startup then at some time later I could hear the RPM decreased almost to a point of stalling and then it rev to 2000 RPM and then oscillated between high and low RPM, then finally to normal RPM.

All this to say, Bearcatdon is correct.

Well it took me about 14 hours. The coolant started out very clean. However after a couple days i had oil in my coolant again. It wasent significant but its there nonetheless. all the gaskets are new and the rtv sealant is not leaking in the engine. Everything was done perfectly to specs. If i drain the coolant its not brown its still green so i'm not sure if the oil is lingering in the resivoir cause i didnt scrub it down. There is also no yellow froth anywhere in the oil cap. Its been about a week and a half. What the hell.

Your coolant is still green? Shouldn't you have used Dex-cool, which is orange?

no you can use the green antifreeze as long as it says it can mix with any color.