Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

youcancallmedusty

Junior Member
Joined
Nov 28, 2022
Posts
13
Reaction score
8
Location
Colorado
First Name
Merrick
Truck Year
1987
Truck Model
v2500
Engine Size
350
Hi, this is my first post but I have been using this forum for information for a while now. I have a 1987 gmc v2500 5.7l. My issue is that my coolant turned from the normal slightly dirty/rusty to black with a touch of green from the Prestone within a couple of days. I noticed I had lost oil pressures week and a half ago, usually idle would be 28-30 and now it is closer to 20 and it bumps up to 28-30 when accelerating. There is no coolant in the oil and coolant doesn’t look oily/milky or sludgy, it just is black. A couple days ago it was pretty normal colored, not especially clean but not as dark as it is now. I recently replaced my radiator and did a flush when doing that so I do not believe it’s from rust or hoses. The upper rear passenger side of the engine has developed a oil leak, it seemed like it was seeping since I would only find oil on the front driveshaft, valve cover,starter and head on the passenger side. When I changed out the spark plugs last week I remember seeing that cylinders 6 and 8 definitely were fouled with oil and oil on their threads. Front driver side of intake manifold has a seeping coolant leak. Other than the black colored coolant, slightly oiled spark plugs, and seeping oil leak there are no other symptoms. Maybe some loss of power accelerating up hills but to be honest the stock 350tbi was never a speed demon with the service body on the back being full of tools. There has been no black, blue, white smoke, other than briefly in start up due to the valves not having seals on them. The truck has not overheated and stays within spec of the thermostat, it runs fine other than less power uphills but honesty that could just be me overthinking it and driving my girlfriends Subaru occasionally and getting used to the peppyness of it. Before I start tearing everything down I was hoping to get some opinions, I did read that it might make sense to try to retorque all the head bolts down in case they had gotten loose,l. If anyone has any other ideas of what could be causing the black coolant and loss of oil pressure I would love to hear it, if it is the head gasket then I would like to get going on it since it seems time consuming to replace and would be my first time doing such a project. I can post some pictures of the coolant color, seeping oil leak and whatever else is need to help me get steered in the right direction of figuring out the issue. Picture is of the truck
You must be registered for see images attach
 

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
3,695
Reaction score
6,683
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
A+ for posting a pic. Lots of folks will chime in soon to take you down the rabbit hole. I would lean towards a blown head gasket. Retorqueing the head bolts won't matter.
 

fast 99

Full Access Member
Joined
Dec 31, 2021
Posts
1,620
Reaction score
2,190
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
If automatic using a coolant pressure tester, warm engine. Put about 5# in the system. Then load the engine [1/4 throttle or less]. If head gasket is bad it will build pressure very quickly. They are all a little different but 10# in less than 30 seconds justifies more diagnosis in that area. Needle should move rather rapidly. A couple pounds in normal 10 lbs is not. Should not have to hold throttle more than 30-45 seconds.

Another way is watching for bubbles in the radiator or using a head gasket tester.
 

youcancallmedusty

Junior Member
Joined
Nov 28, 2022
Posts
13
Reaction score
8
Location
Colorado
First Name
Merrick
Truck Year
1987
Truck Model
v2500
Engine Size
350
A+ for posting a pic. Lots of folks will chime in soon to take you down the rabbit hole. I would lean towards a blown head gasket. Retorqueing the head bolts won't matter.
thank you for the welcome. At this point I am hoping it’s the gasket instead of the head or cylinder wall cracked. I drive it pretty carefully and rarely go above 65-70 just to save on gas and it’s no use competing with the modern cars on the road. I figured re torquing the bolts was a long shot but when reading another thread on another forum it had me hopeful. I treat it well and it has a pretty comfy and pampered life since I got it, it’s slowly getting upgraded but I have no clue about before.
 

youcancallmedusty

Junior Member
Joined
Nov 28, 2022
Posts
13
Reaction score
8
Location
Colorado
First Name
Merrick
Truck Year
1987
Truck Model
v2500
Engine Size
350
If automatic using a coolant pressure tester, warm engine. Put about 5# in the system. Then load the engine [1/4 throttle or less]. If head gasket is bad it will build pressure very quickly. They are all a little different but 10# in less than 30 seconds justifies more diagnosis in that area. Needle should move rather rapidly. A couple pounds in normal 10 lbs is not. Should not have to hold throttle more than 30-45 seconds.

Another way is watching for bubbles in the radiator or using a head gasket tester.
It’s a standard. Would that technique still work with that? I am assuming not since you asked if it was automatic but if there is an similar test with a standard I’d love to hear it
 

fast 99

Full Access Member
Joined
Dec 31, 2021
Posts
1,620
Reaction score
2,190
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
Not really, would be hard on clutch. Cant drive and watch the tester. If coolant is discoloring that quick there should be other symptoms like overheating, pushing water out, ect.

A couple times I found excessive voltage in the coolant from a bad ground. Caused discoloration from metal. However, there were other symptoms such as eating the heater core on a month.
 

squaredeal91

Full Access Member
Joined
Mar 10, 2023
Posts
1,787
Reaction score
3,141
Location
Cave junction Oregon
First Name
Greg bush
Truck Year
1991 SB
Truck Model
K30
Engine Size
5.9 Cummins 12 valve
Welcome from Oregon! And this is a pretty curious problem/ occurrence imo
 

squaredeal91

Full Access Member
Joined
Mar 10, 2023
Posts
1,787
Reaction score
3,141
Location
Cave junction Oregon
First Name
Greg bush
Truck Year
1991 SB
Truck Model
K30
Engine Size
5.9 Cummins 12 valve
Have you checked water pump for play? In reference to coolant discoloration. I'm guessing that there's another reason for oil pressure loss. Possibly a faulty oil pressure sender not sending correct reading. But that don't account for power loss up hill unless it is just a heavy Chevy
(Gmc)
 

Durwoods85

Junior Member
Joined
Feb 21, 2014
Posts
9
Reaction score
8
Location
S E Indiana
First Name
Darren
Truck Year
1985
Truck Model
K20
Engine Size
350
I had a similar situation several years ago with my 85 GMC 4x4 3/4 ton that I never found the answer to. Cab was almost rusted so badly I just parted it out. It had a Jasper rebuilt 350, manual trans. Was driving one day and noticed oil pressure went to zero. Checked oil and it was way low (no issues before). Happened to notice coolant overflow tank was dark, full of oil, also oil in radiator. No coolant in oil, but oil in coolant? After parting out truck I pulled the heads but didn't find any obvious sign of blown head gasket but did notice that the Jasper engine had .060 over pistons so I didn't figure it was worth rebuilding. Funny thing was it ran fine!
 

Albrigap

Full Access Member
Joined
Jan 16, 2021
Posts
68
Reaction score
69
Location
South Dakota
First Name
Alan
Truck Year
1991
Truck Model
Suburban
Engine Size
350
These used a steel shim head gasket so retorquing the head would not hurt anything. Getting at the lower row of bolts under the exhaust manifold will be very tough though. The oil pressure exceeds the coolant pressure so you can now have oil in the coolant. When engine is off, you should be able to see the oil floating on the top of the antifreeze. You can use the test kit that goes into the radiator neck and samples the air in the radiator while the engine is running. If combustion gasses are present in the radiator, the fluid changes color. This is a great method of testing to determine if you have a leaky head gasket. Test before ripping things apart?
 

Forum statistics

Threads
42,087
Posts
908,642
Members
33,560
Latest member
bgeise
Top