brown goo under radiator cap

[dtbjan]

Hi all,
This is in reference to my 1993 2.3 with manual transmission.
Here's what's going on:
Today I noticed some brown sludge in the radiator (pics below). It was also pretty low on coolant. I have had a slow coolant leak for a long time, but I haven't been able to find it. I suspected a head gasket leak. I did a compression test, but that looked good, so I let it be thinking it was a hose clamp or something. I just topped it off when needed.
Now this brown sludge makes me think it's another issue. It is also leaking more quickly.
The oil still looks clean. There does not appear to be water in the oil.
Does this look like oil in the water or possibly just rust?
Other symptoms:
Idle is a bit sporadic and sometimes drops low for a few seconds then goes back up. I replaced a coil pack a few months ago and that fixed the idle issue, but now it's back.
sometimes the throttle sticks. If I get up to speed, and take my foot off the gas, the truck doesn't decelerate. and if I put the clutch in, the idle gets really high. I have to turn it off and crank it again. This only happens sometimes.
Lastly: it will start to run hot if I'm idling with the AC on. I assumed this was due to air in the cooling system.
Are all of these symptoms related? I haven't done another compression test. I suppose that is the next step.
I will also test the coil packs again in case that is causing the idle problem.
What do you think about the brown sludge? I've added a couple pictures.
https://imgur.com/a/9Fti2B4
Thanks for your advice,
Duncan

 

[adsm08]

Copper stop leak and rust.

 

[Dirtman]

I was gonna say... Looks like you went overboard with the bars leak. If you start flushing now it may be cleaned out in time for summer.

 

[dtbjan]

Hmm, interesting. I've owned this truck for four years and I've never put any leakstop in. Is it possible a previous owner did and it's showing up now?

 

[anchoredinchrist]

What are you using for antifreeze? Looks like there was plain water used in there. Don't put stop-leak in there though! Being a mechanic I've seen too many disastrous results of that. I'd recommend a good flush and then do a pressure test to find the leak.You can get a uv dye for antifreeze, but normally you can see it drip, unless the leak is internal.

Sent from my KYOCERA-E6790 using Tapatalk

 

[dtbjan]

I've been using 50/50 green antifreeze. I'll give it a go with the pressure tester. good to know it doesn't look like oil. I'm hoping that's a good sign.

What is the best method to flush? Also, is there a block drain?

Any ideas in regards to the idle issue? Likely unrelated?

Thanks again.

 

[adsm08]

Any ideas in regards to the idle issue? Likely unrelated?

Thanks again.

Replace the IAC. It's sticking.

 

[dtbjan]

I did a few radiator drains and refills. seems to be running clearer. I don't have the correct cap for the coolant pressure tester, and the generic one doesn't seem trustworthy. the Rad cap is looking a bit nasty, so I think I'll replace that and see if I'm still losing coolant.

I pulled the throttle body to get at the IAC. I noticed some fuel smelling residue in the upper air intake manifold. Is this a bad fuel pressure regulator? I pulled the vacuum line on the regulator. It didn't seem wet, but hard to tell. It's not a lot of residue, but definitely smells like fuel.

It looks like a real pain in the ass to remove the fuel pressure regulator if that becomes necessary. Its got 3 allen head screws going into it through a plate in the fuel rail. any tips on accessing them if I do need to replace the regulator?

I gave the IAC a cleaning to see if that fixes it. If not, I'll order one.

Thanks for the help.

 

[mikkelstuff]

Redish brown gunk can be a sign of exhaust gas leaking into the coolant system and reacting with the antifreeze. I had this happen with my 1975 Ranchero 460. Cylinder compression was fine but clearly there was a leaking head gasket seal.

All cleared up when I pulled the heads, ground the valves, and reinstalled with new head gaskets.

 

[tomw]

As for the brown goo, I would flush the cooling system, maybe get a reverse flush Tee, drain, add 50% antifreeze volume, and fill the rest of the way with fresh water. Run for a while and see what happens.
A good system will develop pressure, and may hold slight pressure to a degree after the system cools down. Most will pull some antifreeze from the expansion reservoir as they cool, reducing the pressure.
Check back in a week, keeping an eye on the expansion reservoir.
tom