Sludge in coolant, high pressure

[guyryan100]

Hi,
I ran my truck for the first time in several years yesterday. Its a crate stock 350 with < 500 miles on it. Yesterday I changed the oil, primed the oil pump, topped off coolant, and ran the engine for about 30 minutes, idling and test driving.

I have 2 issues and I'm not sure if they have the same cause.

Issue 1: Black sludge in the radiator. It is on the cap and everything I can reach with a finger is coated in it.


Issue 2: Black coolant leaking from the water pipe above the thermostat. This black coolant began leaking out almost immediately and at a steady stream. The clamp is very tight. It seemed like that pipe was under very high pressure and very hot, I noticed it almost immediately after startup.


The engine temp reached about 210 when idling. Initially I didn't have my electric fans connected, once I did the engine temp came down but still saw leaks in that location, always black water. But something seemed wrong to me on the cooling system even before I found the sludge. I even checked that my water pump is not running backward (its a stock pump, serpentine belt, turning counter clockwise).

Im sure I have oil in the water, I'm surprised to see a of of this sludge stuff since the engine is new. The oil I just put in was the first oil change. The previous oil had less than 500 miles on it. I saw no sludge in the radiator when I topped it off yesterday.

Also might be relevant, I have not set the timing except by ear. Its close enough that it ran smoothly and quietly but its not dialed in.

[72SB]

Not running an engine for several years that maintained coolant in it....will often not end well

It will take several flushes to clean it. Might just want to take radiator to shop to boil it out. Remove T stat and block drain plugs and flush the block until clear water comes out

Your heater core will need the same

"If" oil from engine has entered the cooling system before the truck was stored...that is another serious issue (blown head gasket and or cracked head)

Did the truck experience overheat before storage?

[guyryan100]

The truck has not overheated, no. Thanks for your help.

[yuccales]

Could that sludge be from before you swapped engines and was left in the radiator and heater core? Hopefully your crate engine is ok and just needs a major flushing as said before. Good luck.

[guyryan100]

I'll flush it and investigate further. It was new radiator and hoses 500 miles ago, old heater box that I don't recall cleaning out prior. I guess that would be best case scenario that the heater core had gunk in it.

[allchevy58]

Get yourself one of these, take thermostat out, disconnect one of the heater hoses and connect this valve in. Connect garden hose, turn on full, when it starts running clear, connect air to it and it will blast crap out. Repeat until you don't get any crap coming out. https://www.supercheapauto.co.nz/p/t...un/573217.html

[72SB]

you don't want to use full garden hose pressure running through heater core

cooling system operates at 15-16 PSI. Running a garden hose likely about 75 psi will be to much. If garden hose is connected pre=regulator on house, the PSI is likely over 100

Just the engine block its OK but heater core and radiators that are clogged, don't turn hose all the way up

[LNP]

Black or dark colored coolant can be dark brown because of rust from the block or heads but you generally only see that if it sat long term so you may qualifiy and/or a weak antifreeze mix. Dark brown can also be from using Dexcool for your coolant. That crap goes bad tunrs the coolant a dark brown and sludges everything nasty bad. Black/brown can be as mentioned oil in the coolant. Check the oil itself as once the engine warmed up it could easily put coolant in the oil. If this is the case since you said you installed a crate engine my guess would be the intake gasket more than the other. Either case flush well to get out as much as you can just dont be surprised if you dont get it all unless you are going to pop all the freeze plugs out and flush the block 100%. I do hope you figure it out.

[72SB]

Original Dexcool was bad as it did trn to a brown sludge quick when GM introduced it in 96. Mostly because it reacted to the anti leak pellets GM used to put in. Now Dexcool has been formulated to not do this

[LNP]

Originally Posted by 72SB

Original Dexcool was bad as it did trn to a brown sludge quick when GM introduced it in 96. Mostly because it reacted to the anti leak pellets GM used to put in. Now Dexcool has been formulated to not do this

Well admitedly I have been out of the garage world since 2010 except for working on my own vehicles. Then and before 2010 I was a lead diaognstic tech and I saw it ruin more engines, cause gasket issues, clog radiators and heater cores than I can count. I still will not use it after all I experienced. What we were made to use in the shop had no pellets in it and I know the Chevy garage here used the same stuff we did. Hope you dont take me wrong I am not arguing thats not my thing on forums. I am merely explaining where I'm coming from.

[Ironangel]

Drain and flush thoroughly! That thermostat housing looks like it's leaking and whats up with that heater hose connection on the water pump, is that just the paint or is the water pump cracked? A new motor will run a little hotter than when it's got few hours on it. My crate 350 just runs hotter than the older motors did. With that said, need to verify the timing, and make sure those heater hoses are routed correctly. The 5/8" hose pictured should go to the lower fitting on the heater core, the 3/4" hose from the top of the core to the upper fitting on the radiator. The 5/8" hose should go a fitting on the right front of the intake manifold before the thermostat. https://www.bing.com/images/search?q...gHaG-&idpbck=1

[BAD1916]

When my Suburban’s block cracked I got no water in the oil but had oil going into the water something fierce. It was never black but was more a light tan and kind of frothy. Nasty

[72SB]

LNP

I understand your concern about Dexcool. Yes GM had issue with it as I mentioned. My 96 came with it and in short order brown sludge (within a year IIRC). The car was under new car warranty and the dealership flushed the system and replaced with green which to this day I still use in that car although it is now a 383

My understanding was GM started all models in 96 with a 100k mi full service Maintenace schedule so needed a coolant that would last that long. Unfortunately, the Dexcool was not up to that task and also the anti-leak pellets GM put in cooling systems then really did react chemically to Dexcool which turned it into brown sludge. I don't know when Dexcool was reformulated, but it was

My neighbor was a mechanic for state road Maintenace (CalTrans) and he said they took Dexcool out of all their trucks as they had issues with the sludge and said also plastic components in cooling system got brittle because of it

With that said my 72 C10 6 cyl had Dexcool in it when I got it. Assume PO ran it. I have continued to use it without issue

[LNP]

Originally Posted by 72SB

LNP

I understand your concern about Dexcool. Yes GM had issue with it as I mentioned. My 96 came with it and in short order brown sludge (within a year IIRC). The car was under new car warranty and the dealership flushed the system and replaced with green which to this day I still use in that car although it is now a 383

My understanding was GM started all models in 96 with a 100k mi full service Maintenace schedule so needed a coolant that would last that long. Unfortunately, the Dexcool was not up to that task and also the anti-leak pellets GM put in cooling systems then really did react chemically to Dexcool which turned it into brown sludge. I don't know when Dexcool was reformulated, but it was

My neighbor was a mechanic for state road Maintenace (CalTrans) and he said they took Dexcool out of all their trucks as they had issues with the sludge and said also plastic components in cooling system got brittle because of it

With that said my 72 C10 6 cyl had Dexcool in it when I got it. Assume PO ran it. I have continued to use it without issue

The problem with it or was then was they replaced the silicates and phosphates that was found in regular anti freeze with new chemicals to make it last longer. Man that didnt work. lol These chemicals ate seals degraded plastic which was used and still is for intake manifold gaskets. They may have changed those chemicals with different ones presently I dont know. But if its working now for you it must be a different formula. Hope you never have any issues with it for me I will stick with green anti freeze.

[lousyflyer]

I just went through this on a car I bought that had been treated with a block sealer. The crud had accumulated in the bottom of the radiator. I flushed it with prestone system cleaner and all hell broke loose.

My crud looked exactly like yours. The system was full of it. Including the heater core.

[Wrenchbender Ret]

I had a 96 Monte that had Dexcool in it. It was fine till I added some a-freeze that said it is to use with any a-freeze. It soon developed that sludge like that.

George

[guyryan100]

Two years later and same issue. At the time I flushed it clear and decided to drive it a while. By a while, < 100 miles in the last 2 years. The water is black and sludgy. I drained the radiator and it was black water. So I've started investigating - I took off the intake manifold and didn't see a clear smoking gun, but I do see lots of black junk in the water passages. So I took off the passenger head. No obvious leaks but lots more black junk in the coolant passages in the head and block.

I vacuumed water out of the coolant passages. See the attached photo. The milk jug has the contents of what I vacuumed out and its black sludge water. The hose you see in the foreground is a clear hose with the black sludge water coming out of the block.

I can't see that this much could leak via a head or under the intake. But I dont know where/how to look for where pressurized oil could be getting in to the coolant.

There is no oil cooler on the truck, there is an AFT cooler in the radiator but I see no signs of red. Only black sludge, lots of black deposits, and a slight sheen in the coolant.

Where should I look?

Ryan

[dmjlambert]

What kind of coolant do you use and what is the mix ratio, and how does the oil look?

[guyryan100]

Over the last 2 years I used standard green coolant pre-mixed. That's what I think I put in 20 years ago too but can't be certain. I've found no evidence of water in the oil, or water under the intake.

[guyryan100]

Here's a photo example of what's in the coolant passages.

[70STOVEBOLT]

Did the oil level go down after driving it 100 miles?

[guyryan100]

I don't think so - I it seems like it would take quarts of boiling oil to make the oil this black.

[dmjlambert]

Is that a dry crust or is it oily?

[guyryan100]

In the water passages its crusty, I can scrape it with a screwdriver and can't wipe it with a rag. In the coolant its a frothy liquid. I figure it was baking on the places it caught onto.

[dmjlambert]

That is weird. pour that sludge water in a clear glass and come back and look at it in a week or so and see if it separates into water with oil on the top. I'm sorry to hear you're having this trouble on a new engine.