1985 720 -- Slight Coolant Loss From Reservoir After Head Gasket Replacement

[720 Rocker]

Hi, New to the forum, but I've been looking in for a few years now and greatly appreciate the opinions and advice given here.  I've had my 1985 Nissan 720 for about 15 years now, and have done 90% of the work on it myself.  The head gasket finally blew recently, causing a great cloud of white smoke as I drove down the Interstate highway to the next exit, where I had it towed home.  Luckily, it never overheated.  In fact, the truck has never overheated the whole time I've owned it, and I've put about 100,000 miles on it since I got it.  It currently has 178,000 miles on it.  I just replaced the head gasket (and intake and exhaust gaskets, of course) with a Fel-Pro kit after days of cleaning the head and block surfaces meticulously.  I did not resurface the head, because I figured it didn't overheat, so, probably okay.  I rolled a round bar over the surface slowly looking for any light between the bar and the head surface, but never saw any light, so, again, I figured I would just clean it as good as possible and replace the head gasket, which I did.  I have a factory service manual (FSM) and followed the torque sequence exactly as specified.  I re-used the old head bolts, but like I did with the head and block surfaces, I cleaned the head bolts meticulously, using a wire brush on the end of a drill with brake cleaner squirts in between.  Then, I put a little light oil between the washer and head of the bolt, as suggested on this forum by DatzenMike, whose opinion and advice I trust greatly!  Anyway, after burning out the oil I put on the cylinder walls, no more smoking tailpipe!  Yeah!  After driving it for a couple of days, I checked the compression with the engine hot, and it was at 150, 148, 149, and 149 (Cylinders 1-4, respectively).  Lower than I expected, but very tight numbers / consistent readings, so cylinders appear to be well-sealed.

 

BUT, I noticed a slight drop in my coolant reservoir for a few days.  It went from the "MAX" level to about halfway toward the "MIN" level marker.  So, I added coolant to reservoir.  I did this twice in a couple more days of driving.  Since then, I haven't noticed that it no longer drops, and seems steady at hte "Max" level marker.  Is this normal?  Was there just some air in the cooling system, perhaps, that worked it's way out?  Should I worry?

[datzenmike]

Sounds normal to me. An air bubble seems most likely. Enjoy!

 

Once a year loosen each bolt one at a time and torque to 60 ft lbs. in any order you like.

[720 Rocker]

Thanks!  Will re-torque as you suggest, datzenmike.  BTW, I just now replaced the original 720 exhaust manifold (cracked on the backside), and noticed the downpipe was toast, too, with a big hole in the metal at the convergence of the fork between the two exhaust ports.  I assume this is a common place for failure.  I already ordered the BRexhaust version of the OEM downpipe, but it doesn't appear, from pictures online, to have the shield hangers built in, like the original.  Any reason I couldn't run the exhaust without the shields?  Are the shields there for heat control/deflection, or for protecting the pipes from road rocks and debris, etc.?  Are the shields necessary? Of course, I will keep the shield on the original catalytic converter.

[datzenmike]

Lots of heat and stress on the welds on the down pipe. Not surprised it cracked. It's a heat shield and you can run without.

[NC85ST]

On 5/31/2022 at 2:57 PM, datzenmike said:

torque to 69 ft lbs.

Or 60 ft lbs?

[datzenmike]

Yeah I hit the 9 rather than the 0. Corrected.

[720 Rocker]

60 ft pounds it is!