I found this forum because of the “Rod Knock Diagnosis and FAQ” post, which is very informative. I’ve also done a lot of searches on the subject, which haven’t answered my questions. So, even though this is not about a Supra, I’m hoping someone will find the puzzle sufficiently interesting to respond.
The car is a ’96 Mystique, which I bought for my daughter at what I thought was a good price. It appeared to be well maintained, lots of repair and maintenance records, lots of new parts, but was not running. The guy, a preacher, seemed honest – thought it was something to do with injectors. I figured it wasn’t injectors, but thought I could figure out the real problem. A leakdown test confirmed that it needed a valve job, so I pulled the head and had the machining done. So, the coolant oil contamination issue discussed in the Rod Knock article might be a concern, but I did drain all the coolant first.
When I put it all back together, it started right up and everything sounded fine. I drove it around the block – didn’t run great, but not bad and made no unexpected noises. After it idled for a while as I checked some things out, it started making some noises intermittently. At first it sounded like a valve tick, but then got louder and it became obvious that it was really coming more from underneath the car – from inside the block (it’s not the hood rattling
. The engine still starts right up, but I don’t want to run it much until I figure out the extent of the damage and if it’s salvageable.
My first thought was that it was an oil circulation problem. One time my son changed his oil and when he started it up afterward, the engine started making all kinds of noise, similar to what this Mystique is doing. It turns out that when he jacked the car up to change the oil he had the jack partly on the oil pan and pushed it up into the oil pickup tube. Once we removed the pan and straightened it out, he had to drive it a few miles before all the noise went away. Never had any trouble after that. Back to the Mystique… so I installed a mechanical oil pressure gauge. At idle the pressure reads 70psi. Give it a little gas and it pegs at 80. This is with 10W40 in it and a new filter. Ford calls for 5W30, but I don’t think this higher viscosity on an engine with 150,000 miles would account for that high an oil pressure. I believe oil pressure is usually measured past the filter and bypass valve, so it seems that those things and the pump are OK.
There’s a video on youtube that shows an engine with rod knock and there is so much play that the guy is physically moving the connecting rod on the crank. http://www.youtube.com/watch?v=NsCb0auCDWI So I thought I could test for that from the top of the engine. I inserted a smooth metal rod through the spark plug holes and jogged the starter motor. When a piston came up to TDC and then started going down, I figured that the crank pin is now pulling on the rod cap and if the bearings are really worn, the gap would be towards the piston end of the rod. I should then be able to push on the top of the piston and it would move down if there was a gap. I felt no movement whatsoever. I don’t know if this is a useful test or not.
Anybody have any ideas what could cause these symptoms? I’m still thinking that it’s an oil issue, and with the pressure high, it seems like a blockage. I think a spun-bearing cuts off oil to that one bearing and might raise oil pressure a bit, but it seems like you’d need a bunch of spun bearings to get pressure up to 70+psi. What is my next step? I was thinking about dropping the oil pan to take a look inside, but I haven’t yet because it’s a pain in the butt – you have to disconnect a bunch of stuff and raise the engine/transaxle 2”. I’ll do it if I can really find something out. Any ideas would be greatly appreciated.
Dave
The car is a ’96 Mystique, which I bought for my daughter at what I thought was a good price. It appeared to be well maintained, lots of repair and maintenance records, lots of new parts, but was not running. The guy, a preacher, seemed honest – thought it was something to do with injectors. I figured it wasn’t injectors, but thought I could figure out the real problem. A leakdown test confirmed that it needed a valve job, so I pulled the head and had the machining done. So, the coolant oil contamination issue discussed in the Rod Knock article might be a concern, but I did drain all the coolant first.
When I put it all back together, it started right up and everything sounded fine. I drove it around the block – didn’t run great, but not bad and made no unexpected noises. After it idled for a while as I checked some things out, it started making some noises intermittently. At first it sounded like a valve tick, but then got louder and it became obvious that it was really coming more from underneath the car – from inside the block (it’s not the hood rattling
. The engine still starts right up, but I don’t want to run it much until I figure out the extent of the damage and if it’s salvageable.My first thought was that it was an oil circulation problem. One time my son changed his oil and when he started it up afterward, the engine started making all kinds of noise, similar to what this Mystique is doing. It turns out that when he jacked the car up to change the oil he had the jack partly on the oil pan and pushed it up into the oil pickup tube. Once we removed the pan and straightened it out, he had to drive it a few miles before all the noise went away. Never had any trouble after that. Back to the Mystique… so I installed a mechanical oil pressure gauge. At idle the pressure reads 70psi. Give it a little gas and it pegs at 80. This is with 10W40 in it and a new filter. Ford calls for 5W30, but I don’t think this higher viscosity on an engine with 150,000 miles would account for that high an oil pressure. I believe oil pressure is usually measured past the filter and bypass valve, so it seems that those things and the pump are OK.
There’s a video on youtube that shows an engine with rod knock and there is so much play that the guy is physically moving the connecting rod on the crank. http://www.youtube.com/watch?v=NsCb0auCDWI So I thought I could test for that from the top of the engine. I inserted a smooth metal rod through the spark plug holes and jogged the starter motor. When a piston came up to TDC and then started going down, I figured that the crank pin is now pulling on the rod cap and if the bearings are really worn, the gap would be towards the piston end of the rod. I should then be able to push on the top of the piston and it would move down if there was a gap. I felt no movement whatsoever. I don’t know if this is a useful test or not.
Anybody have any ideas what could cause these symptoms? I’m still thinking that it’s an oil issue, and with the pressure high, it seems like a blockage. I think a spun-bearing cuts off oil to that one bearing and might raise oil pressure a bit, but it seems like you’d need a bunch of spun bearings to get pressure up to 70+psi. What is my next step? I was thinking about dropping the oil pan to take a look inside, but I haven’t yet because it’s a pain in the butt – you have to disconnect a bunch of stuff and raise the engine/transaxle 2”. I’ll do it if I can really find something out. Any ideas would be greatly appreciated.
Dave