High first runnings gravity, low overall efficiency?

Is a high first runnings gravity but a low overall efficiency the sign of a poor crush?

I have failed to achieve anything over 65% with my false bottomed keg MLT. I do conversion checks with Iodine, hit and hold my mash temps, stir my mash on a regular basis, calibrate my thermometers and hydrometers on a regular basis, lauter extremely slow during my fly sparge, use hot sparge water and take regular gravity readings during my lautering, use a sparge arm, avoid channeling and maintain a nice level above my grain bed but I can't seem to break the 70% mark.

On my last brew I took three gravity readings before I boiled. The first runnings reading which was taken within the first gallon was 1.083. The second was at 7.5 gallons and was 1.050. The last was at 13 gallons and was 1.010. Using the beer recipator I rechecked after all was said and done and sure enough hit 65% just like I always do but one thing didn't add up to my brew buddy and I. It coughs out a figure stating that my estimated first run off should be 1.067 if my efficiency is as low as it is but my initial runoff was much higher (1.083). I bumped the efficiency field up until I met that figure and it indicated I would be running at 80% efficiency. Granted, these are only estimates and every system is different.

It did however suggest something to me. Is it possible that I have an inefficient crush which when mashed in an efficient tun at a proper temperature leads to a really decent conversion and concentration of sugars but which renders poor access to the entire volume of sugar held in the grain? It almost seems to me like my MLT and mash are chewing through the sugar and working really well but then as the sparge starts run out of available sugar too early.

Next batch I will probably grind myself with a friend's mill and hopefully I'll get better results.

I think you're right. If your iodine is telling you you're at full conversion and you're still having efficiency issues, it sounds like you're crush isn't getting enought starch into the mix. Grind until you're scared and see if you get a bump up.

A poor crush is one possibility, but you can make up for that to a certain extent by mashing thicker or mashing longer. Both of these will change the flavor profile of the beer. Mashing thicker should produce a more dextrinous wort, and mashing longer will produce fewer dextrines.
If you can borrow a mill that is known to give good results, I think that would be a much better place to start rather than messing with the mash.
Other possible mash problems could be caused by poor water chemistry (insufficient calcium, or bad pH) The pH could be treated by 5.2 buffer from 5 star chemicals, but this won't help if you pH is good to start with. Lack of calcium could be treated with calcium carbonate (raises pH) or calcium sulphate (lowers pH). If you are not using brewing salts, a water analysis should give you a good idea of the amount of calcium in the water. Your water supplier can probably tell you how much calcium is in the water See How to Brew - By John Palmer - Using Salts for Brewing Water Adjustment for some good information on water treatment.
It has been my experience that the lautering process is much more likely to result in poor efficiency.
I brew 5g batches using a round cooler with false bottom, and a sparge arm to fly sparge. (A junior version of what you have.) I collect about 6.75g from the sparge.
I usually take about 60 minutes to sparge a beer with a gravity of 1.045, and this extends to 90 minutes for a beer with a gravity of 1.070. I would guesstimate that your times should be increased by about 50% to account for the larger volume.
I increased my efficiency by 10% simply by adding a mash out at the end of the mash. In my case, I added about 1g near boiling water. In your case, it would need about 2g. Before I did this, I measured the grain bed temperature during the sparge. It never got above 155F! After the mash out, the entire sparge was conducted in the upper 160's. I was also surprised by how much my sparge water cooled during the transfer from the HLT to the grain bed. I now heat by sparge water to 185F, add it to an unheated HLT (a 5g cooler) which drops the temperature down to 180 - 182, and the water exiting the sparge arm has dropped to less than 170.
In addition to monitoring the grain bed temperature during the sparge, there is one further test that is worthwhile when the sparge is complete. After stopping the collection, add another 1 - 2 gallons sparge water to the MLT, and then stir really well. This will dissolve any remaining sugars that have not been collected in the MLT.
After waiting about 10 minutes, collect enough wort from the MLT to perform another gravity check. When it has cooled, check the gravity. If it has risen at all, then you have channeling problems, probably caused by sparging too fast. When I did this test, the gravity after adding an extra gallon water was well under 1.010

Hope this helps

-a.

Dumb question, but you are adjusting your gravity readings for temperature correct?

I cool my wort to room temp before taking gravity readings and if I've over or under cooled by a few degrees I adjust accordingly and I treat water according to what it needs based on my local water analysis.

Yeah I know necro post but I came across this looking for something else, figured someone else might too.

To clarify, the efficiency % given in the first post was 65%, is this overall brewhouse efficiency, or mash efficiency? I know when I use beersmith I keep mine set at about 65-70% for overall but it shows my mash efficiency at 80% or higher on most of my brews. Also at a water/grain ratio of 1.25qts/lb your first runnings should be in the neighborhood of 1.080 - 1.085.