Overheat coolant - SD25 D21 1987 Nissan

#91

ill be gone all day so ill get a photo tomorrow.

the glow plugs all have their tips (i should hope so, they're pretty new)

#92

#93

Top left, top right, lower left photos are of the same cylinder. The small shiney, carbon free spot on the piston crown is usually due to one of two reasons. (1). crankcase oil is passing into the combustion chamber at that point.
(2). engine coolant is passing into the combustion chamber at that point.

Bottom right photo looks okay. So two down, two to go.

#94

philip wrote: (1). crankcase oil is passing into the combustion chamber at that point.
(2). engine coolant is passing into the combustion chamber at that point.

philip wrote:The crankcase blow-by these gouges allow would not be noticed in an SD25 due to the closed crankcase vent system.

philip wrote: All engines develop blow-by with age.

so if its oil passing into the combustion chamber thats alright?

and if its coolant?

and i guess ill get you good photos of the other two cylinders

#95

after oil wrote:so if its oil passing into the combustion chamber thats alright?

and if its coolant?

and i guess ill get you good photos of the other two cylinders

1. When the pistons are fitted with single piece oil rings, it's to be expected at higher mileages. If you magnify the clean spot, you'll see it extends north about 3/8".

2. CLOSELY inspect corresponding area of the head and both sides of the head gasket.

3. It would be helpful to ID each cylinder by #.

#96

i noticed that the squiggle that looks like a 2 on one of the pistons is: a 2.
the pistons are etched w/ numbers near the stamped 5.

i cant inspect the head.. its at the head shop. i was hoping they would have some info for me before they closed friday, but alas no. rumour has it, though, that its flat. i havent heard about the magnaflux yet. its CAD$65 to resurface.. should i have it done anyway?

i uploaded photos of cyl 3&4 our esteemed admin will resize them tonight.

#97

after oil wrote:-SNIP- i havent heard about the magnaflux yet. its CAD$65 to resurface.. should i have it done anyway? -SNIP-

Always resurface when the head gasket mating surface is mostly if not all metal. As I mentioned earlier, there is in excess of 425 psi cranking compression to say nothing of much higher pressures at peak combustion.

In your specific case, there is evidence of pressure leakage between cyls 2-3 and etching around each cylinder and several coolant passages. $65 CAD well spent.

#98

If the head is flat, and there is no corrosion evident, I would probably not have it surfaced. But it would certainly be very clean before I put it back on.

#99

cylinder 3:

and last but not least 4!

#100

Ok. Now that we've got all four cyls to examine, I'll put (apparently) cyl #1 being questionable.

As I mentioned earlier, bare metal/clean spots like this come from oil passage (not unusual for single piece oil rings) or coolant leakage "steam cleaning". If you examine closely you'll see the carbon has been eroded away ... not suddenly chipped away. With this sort of "steam cleaning" it's a matter of quantity and time meaning ... your oil may well NOT -appear- contaminated.

Remember, since there is this evidence, your head and block surfaces need to be ... PERFERCTLY true. You've got to put the time in cleaning the block surface of all adhered debris and rust. As for the head, resurfacing will be optimal.

#101

i am sure that is cylinder number 1.

i know this may be elementary, but how should i clean it?

can i test the block for trueness w/o pulling it?

#102

Because I'm a lazy butt right now, and because GOOGLE is still speaking to me, please go to: Head Gasket Basics

#103

hey folks....
i just talked on the phone to the guy at the head shop. he spoke of two issues:

A: a crack between the valve seats, in one of the cylinders on the end. (he couldnt remember off hand 1 or 4)

asavage wrote

Lightening up and zooming in, I think that I see two cracks between the valve seats on cyl. No. 3.

he says the crack between the valve seats is almost never a problem, except on chevy's. i could send it away to have it pressure tested for $100, but he says ill probably be wasting my money.

B: the big problem was probably head gasket failure between a cylinder and a cooling port, but again didnt say which one. said they could tell by looking at it. so my photos should tell all.

the head will be planed and ready for tomorrow.

should i worry about the cracks between the valve seats?

#104

Were coolant entering at the crack(s) there would be "cleaning" evident such as found on the edge of one piston crown.

Clean the block's deck within a mm of its life.

#105

after oil wrote:the head will be planed and ready for tomorrow.

So based on this statement they must have told you the head is warped? If it isn't I see no value in having it planed, and I assume they know it cannot be planed with the prechambers installed?

after oil wrote:should i worry about the cracks between the valve seats?

That's what the pressure test would findout, whether the cracks are far enough past the valve seats to create a compression leak.

If all you had was gasket failure and there was no head warpage I would spend my money on the pressure test and do a thorough cleaning of the existing surface. I would hate to have it planed and reinstalled only then to find that there's a compression leak.

steve a

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