Valve tappet noise or knocking when hot

[tjp74]

Sorry if I posted a repeatedly discussed subject.

My recently aquired 00 D2 has developed a new problem. As some of you may know, this was purchased with occational overheating problem. When I got the car, it didn't overheat a bit and ran fine untill last week, it overheated again on interstate, Pulled over, let it cool, drove some more, pulled over and called AAA.

anyway, after replacing the thermostate, overheating problem seems to have gone away but a new problem. When engine reachs full operating temperature, needle at exactly half way, and let it run for few minutes, I start hearing what apears to be a valve tappet noise or some sort of knocking. It seems noise is coming from valve cover area or under the intake manifolds. It's not a faint noise. You can clearly hear it from inside the car with all door closed when idling. I think noise doesn't get louder as I rav the engine but knock frequency increases as RPM obviously. If I turn off the engine at that point, let it cool down for 5-10 minutes, noise goes away. Then let it run for another 5 minutes, noise comes back. So it only happens when engine is in full operating temperature. Engine idles and ravs fine cold or hot but I haven't drove it yet.

I understand that valve is not adjustable and this car just got the headgasket replaced.

Is this engine done?
Or is this can be fixed relatively easily? I am thinking bad valve lifter but that will require pulling heads one more time and that's a major job. Any chance rod bearing issue?
Should I try different weight oil? Oil looks clean and is a synthetic blend. I didn't check the invoice to see what weight was used.
It's got 65K miles and head gasket was replaced only few hundreds miles ago.

If needed, I am willing to take some video and post here.

What other info do you guys need?

 

[Disco Mike]

I would not drive it till you can verify oil pressure at all four temp ranges. If the pressure is good then I would suggest you pull the oil pan and intakes to do a visual inspection.
Let us know how it goes.

 

[tjp74]

What would be the 4 temperature ranges? So the fact that I don't get old temperature warning light doesn't mean pressure is good?

 

[Disco Mike]

There is no such thing as a cold temp light.
The oil pressure needs to be checked when stone cold at idle and 2000 RPM's and then at operating temp both at idle and 2000 RPM's.
Get back to us with your numbers when you can.

 

[tjp74]

There is no such thing as a cold temp light.

I meant to say low oil pressure warning light but I was thinking about coolant temperature gauge when I was typing it.. duh...
And I realized that light only comes on when pressure is dangerously low to run then engine so it's not a dignostic tool.

Anyway, I started up the engine today after work (I am not driving it) and noticed that the noise definitely goes away as I rav the engine. I would say 1000 rpm or higher, noise goes away completely. If I let off the gas, noise returns after 1-2 seconds. And noise definitely comes from under the intake manifold.

So, I am 99% sure it's the valve tapet noise and it's related to oil pressure. I havne't hooked up the gauge yet but what ever the pressure is at idle and only when hot, it is not enough to supply required oil pressure to all valve lifters. It's hydraulic lifters correct? Or couple lifters are worn or defective so it requires higher pressure. I am not looking forward to replace lifters as I assume this requires complete removal of heads. I hope it's an oil pump or clogged pickup screen. How hard is to drop the pan? It doesn't look too bad just looking at it. I am assuming oil pump can be replaced with engine in place. How hard is it?

But I am putting the gauge and checking the pressure to comfirm this over the weekend. I guess trying heavier weight oil is another way to comfirm this. At least I don't think I killed the engine yet.

 

[greg409]

Replacing lifters does not require removing heads, but the rocker ass'y and intake have to come off.

When lifters "wear out " it's the bottom cam lobe contact surface that becomes concave.
If they "tick", it's almost always due to foreign contaminents, ie "sludge to varnish"

Have you tried using engine flush in oil?
(I don't use synthetic, so don't know if flush is the same)

I had lifter tick on my DI, flush did resolve it after a few weeks of driving with (2) oil changes
(I was using 10-40 at that time)

Let us know how it goes, please

luck,greg

 

[Disco Mike]

Don't try a heavier oil, check the pressure first, if bad all the way across then pull the pan and make sure the pick-up tube is clear.

 

[greg409]

I agree with Mike, the first thing you should do is determine your oil pressure.

Heavier oil may raise your oil pressure slightly, but it'll do nothing to reolve sludge.

You state the pressure will turn on your oil light & result in lifter tick at idle

I can't tell you how satisfying it is to pull the pan,oilpickup and de-sludge them

(I found a chunk of old pan gasket in my pickup screen.)

If you put your truck up on jackstands,(on frame), and let the axle back down, you can remove the pan quite easily.

luck,greg

 

[Glen]

The tappet noise (knocking) description above is identical to that coming from my '95 3.9 V8 disco. Only when fully hot, stops at revs, stops after motor cools a bit. I was wondering what the outcome was.

 

[tjp74]

Since then I've learned a lot on Rover V8. I heard that there are many reasons for such noise, Some will just tick like that naturally and go on without much problem.

In other cases, it could be the dropped liner moving up and down noise.

In my case, my finding is inconclusive but I definitely seem to have a crack behind one of liners as exhaust gas appears to be leaking into the coolant. I am not sure it's it's dropped liner. Could be combination of two. No coolant into the combustion chamber but just opposite. Coolant would bubble and no matter how I bleed the system, air pocket would form eventually pushing all coolant out and overheat. I end up source an used engine and replace the whole thing. No more noise, no more overheat.