Blown head gasket or worse?

[箱720]

I had a coolant hose blow unbeknownst to me on my 1986 720 and the engine overheated. Since then and replacing the coolant hoses, the engine has been making an odd noise, almost like a rod knock. Checked the oil and it is a grey watery mix with swirls in it where something is separating from the oil. Couldn't tell if there were any small metal shavings in there. Checked exhaust too and it has oil coming out of it as well. I'm fairly certain the head gasket blew, I just dont know how bad the damage is. I pulled the valve cover but everything up top looked fine. Is there any way to tell what it may be without pulling the whole engine apart? I dont want to have a couple hundred dollar fix turn into a couple thousand-dollar fix.

[Stoffregen Motorsports]

Depending on how long you ran it while it was overheating, things could be bad. Anything from bent connecting rod to spun rod bearing to cracked engine block and head.

 

First thing, remove the head and inspect.

 

Honestly though, doesn't sound like you know a whole lot about engines, so this may be a steep learning curve. Not trying to dissuade you, just pointing to the scoreboard.

[箱720]

34 minutes ago, Stoffregen Motorsports said:

Depending on how long you ran it while it was overheating, things could be bad. Anything from bent connecting rod to spun rod bearing to cracked engine block and head.

 

First thing, remove the head and inspect.

 

Honestly though, doesn't sound like you know a whole lot about engines, so this may be a steep learning curve. Not trying to dissuade you, just pointing to the scoreboard.

The concern I have is if the block is damaged in a way that I cannot see, such as a hairline fissure. I just don't have the tools to be able to detect that, and I just dont have the time and know-how to do a full engine rebuild. I know it's hard to tell without knowing everything I've put into it and whatnot, but if it's more than the head gasket, do you think it's worth just doing a whole new motor swap?

[datzenmike]

You would have to overheat it pretty bad to damage the engine. Well other than warping the head. Head gasket is almost certainly blown from description. Coolant gets into cylinder, turns to steam and is compressed past the rings and condenses in the crankcase and mixes with the oil. If the engine is wrecked knowing will only cost a new head and possibly having the head milled flat.

 

Before we rush into things here's what you must do before turning a wrench. You need to know how to block your timing chain tensioner from falling out when the chain goes slack when the cam sprocket is removed. You my know or you may not. If it falls out the entire front of the engine has to come off to correct. Add 3-4  hours work.

[Logical1]

My money is on blown head gasket, block is fine, head maybe slightly warped but doubt it. Search on Ratsun for the head removal and wedging of timing chain. Head gasket=$20 new oil, coolant, and oil filter=$60. I have done several 720 head gaskets in an a couple hours.  

[bottomwatcher]

"Rent" a compression tester from autozone. It's free as long as you bring it back. It will be obvious of a leaking head gasket. The other signs already point that direction.

[箱720]

1 hour ago, datzenmike said:

You would have to overheat it pretty bad to damage the engine. Well other than warping the head. Head gasket is almost certainly blown from description. Coolant gets into cylinder, turns to steam and is compressed past the rings and condenses in the crankcase and mixes with the oil. If the engine is wrecked knowing will only cost a new head and possibly having the head milled flat.

 

Before we rush into things here's what you must do before turning a wrench. You need to know how to block your timing chain tensioner from falling out when the chain goes slack when the cam sprocket is removed. You my know or you may not. If it falls out the entire front of the engine has to come off to correct. Add 3-4  hours work.

Ive heard the block on the z24 engines are pretty bulletproof. As long as that is fine, I can work with it. Would a head gasket make that knocking noise though? The sound doesn't seem like it is coming from underneath so much as from everywhere. I assumed it was maybe just misfiring that was making the noise? The rpms do occasionally jump on idle.

[Stoffregen Motorsports]

Well, either way, the head has to come off to find out.

 

Like Mike suggested, search here how to block the timing chain, and also, start at TDC on #1 cylinder before teardown.

[NC85ST]

21 hours ago, 箱720 said:

that knocking noise though

What you’re hearing could be a bad spark knock as a result of a blown head gasket. I’ve had that happen to my truck when it blew a head gasket.

[Thomas Perkins]

About 1500 to do the head gasket around here.The head may be warped.Need to send out to a machine shop,have the valves adjusted.I always send mine out to get done.They will pressure test it too.Also check the cat for blockage, get rid of it if you can.I did.Mine has new head bolts and new timing chain.

[powderfinger]

The head gasket is a job that can definitely be done yourself. No need to pay someone $1500 to do it when the truck likely isn't worth too much more than that unless it's in really good shape. It is not a difficult job as long as you do a little reading. Even if you don't have a lot of experience working on vehicles, if you are mechanically inclined and have some common sense you can certainly do it.

 

If you fear the head is warped, always possible since you did say it overheated, you can either buy a machinist straight edge off Amazon and check it yourself or let a machine shop check it it for you. 

[Thomas Perkins]

I Pay and don't have the time to do it.

 

 

 

Edited September 11 by Thomas Perkins

[bottomwatcher]

This is a relatively simple repair. I did it the first time when I was 17. I did drop the tensioner so that is really the most important thing not to FU on.

[datzenmike]

What's a mechanic's rate??? $1,500 is what? 15 hours? 12? to do a less than 8 hour job? Probably much less as a mechanic has place and tools. $1,500 is a "Piss off I don't want to do that job go away".   

[Stoffregen Motorsports]

Some of the shops around here are up to $250/hr now.

 

My rate is a relatively low $150/hr.

[powderfinger]

Biggest reason for my comment about not needing to pay someone to do it is, I am sure there are lot of people that are both regular members of this forum and likely the majority of the ones that just jump on once or twice to ask how to fix something that cannot afford to pay a shop to do it. Likely why they are driving a 40 year old truck in the first place. On top of that, if you don't have a mechanic that you know well you are really rolling the dice on whether or not you will get quality work out of them.

 

There is also nothing like the satisfaction of the first start and drive after fixing something like this if you have never done it before. Gives a person confidence to keep it up.

Edited September 11 by powderfinger

[Thomas Perkins]

Don't have time to do major work.I feel better getting it done right.I've had about 3 blown head gaskets in 30 years and they have done it right.Even had a Jasper engine installed by a Jasper installer back in 2009.Jasper only sells to installers.I have 106,000 miles on it.Check out my 39 year old truck.I am doing something right.

[Stoffregen Motorsports]

1 hour ago, powderfinger said:

 you are really rolling the dice on whether or not you will get quality work out of them.

 

Here I come in defense of the shade tree mechanic again.

 

It's not always a matter of poor quality work. Many times it's time constraints (the owner of the car says he/she can't spend a lot), or it's not having the car long enough to be able to find all the problems with the car, or it's that the problem occurs infrequently and cannot be duplicated.

 

Engine repairs can be problematic, especially when repairing engine damage. The only way to fully understand what the engine needs is a full teardown, and now you're talking engine rebuild. You can make a good guess based on removing the oil pan and a couple rod caps, checking the deck of the block for cracks, etc, but you don't know what you can't see.

 

So the guy who quotes you for an engine rebuild when all you think you need is a head gasket, he's probably been around the block a time or two and knows what to expect.

[datzenmike]

My bad. Did not know the actual price of mechanics. The only time one of my Datsuns was in a garage was to install new tires on my rims and balance them and that was my 33s on my 620 and was free. 510, 521, B210, '74 and '76 710s were never near one. Rebuilt two different engines for the 521 and replaced the 4 speed, rebuilt the A14 on the B-210. Any amount of brake shoes and pads, alternators, fluid changes, radiators, differentials, the list is endless. 

 

So what do you make an hour? Is it $150 to $250????? If it's $30 an hour makes little sense to work 5 to 8 hours (plus tax) to pay for just one from a mechanic, does it???? On top of that the Datsun is older then the mechanic and he's never even seen a carburetor as they disappeared in early '80s.

 

 

[Stoffregen Motorsports]

I've been doing this a looooooong time, and it's never just a head gasket. Even if that is all it takes to repair the engine, which it isn't, there is a cause that you need to track down and repair. When I was doing a bunch of 22re head repairs, I wouldn't mess around with the original heads, I would have a new one ready to bolt on. I also would replace the radiator, no questions. Your Toyota would run better than new when it left here. Fifteen years ago when I was doing these repairs, it cost $1500 to get the job done in my shop.

 

I don't make my full labor rate, even though I am self employed. I have overhead which needs to be paid. No rent, since I own the building, but still, lots of other expenses.

[powderfinger]

3 hours ago, Thomas Perkins said:

Check out my 39 year old truck.I am doing something right.

Certainly didn't intend to imply that you were doing anything wrong just different that's all. I trust my old Nissan as much as I trust my newer truck and my Nissan has certainly never been to a shop to have someone else work on it. To each his own.

[Thomas Perkins]

Wish you live here in Georgia.You could show me a thing or two.I amstill waiting for my other brake cylinder from O'Reilly's.Maybe it will be here today.I got my 2 clips that hold the emergency secondary brake.Just in I ever need some.A little over 4 bucks for them.Got themlocal.Free shipping.I am.putting a rack and pinion on my wife's 2004 Lincoln LS.I got the part from RovAuto Parts.'.I havea great shop manuals that tell you the part number.Way be than Nissan's.3 big books.

[DwayneOxford]

New hoses are cheap insurance.

Bottom is worst. It goes and you wont know till it's too late.

Edited September 12 by DwayneOxford

[datzenmike]

Hoses rot from the inside out s not really visible anyway. Squeeze, if soft replace. Always use 50/50 mix of antifreeze coolant to get the most life out of hoses.