6.9 Block Heater Cracking Issue

Howdy y'all!

My '85 F-250 6.9 is a really, really hard starter in the cold (takes a lot of cranking). Glow plugs are fine, new injector pump is in, etc. Still need to get a compression test and try to figure out the main issue (she's a bit of a hard starter on warmer days too, but nowhere near as bad as when it's below 30).

The motor's got a block heater installed, but I'm not sure if the '85 castings (exact build date is September 1985) are prone to the block cracking issues caused by block heaters of previous years. I've combed through multiple forums trying to find out about the '85 without much luck. If my block is prone to that issue, I'll just end up going with a heater wrap for the fuel filter or something along those lines, at least until I can figure out the main culprit behind the hard starts.

Any help is much appreciated

There are different kinds of block heaters besides the ones that go in a freeze plug in the block. I have a 90 with a 7.3 IDI in it. when the block heaters went bad, I put one in the heater hose( got it from NAPA). it has a pump inside of it and it heats and pumps hot coolant through the whole system. This means that the heater and defroster work as soon as you start the pickup.

The reason I did this is not because of the block cracking issue as I have heard of that. The reason I did it is that it only took about an half hour to install instead of the several hours to half tear the pickup apart to replace the stock ones.

Just an FYI

I haven't heard of that with the 6.9's but I don't follow diesels much.
Just googled it and found a good (last) post in this thread by a 'familiar face':

https://www.ford-trucks.com/forums/1473507-6-9-block-casting-number.html

Sounds like there may be a few visual indicators you can look for.

I agree with Steve in that the circulating heaters are nice. We have a couple of those on our gas tractors.

When we were stationed in Alaska, my 76 f250 came with a block heater, and it just did not do the job. I installed a heater hose heater. Worked like a charm, and most of the time no problem turning the motor over. We also had a heating plate glued to the transmission. And an electric heater in the cab.
There were a few days every winter, when it was down to -50 or so, we had to use the kerosene heater to blow hot air under the truck, so it could be steered.

We also used the heater hose heaters on all our vehicles when we lived in Vermont.

I don't know why block heaters are bad, but U-techcenter has 3 available OEM core plug heaters for $20 + $5 shipping.


https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F164130558968

Jim, I dident say they were bad, I just said that they are a PITA to change while the engine is in the pickup. As in half pulling the engine to replace them PITA. That being said, I told him about an easer replacement that works as well, or I think, better, and takes less time as long as the old block heater is not leaking.

Ugh, I can't imagine that kind of cold or maybe don't want to.

Jim - nothing wrong with block heaters (unless using them with a prone-to-crack block I guess ). They just don't work the same and thus have a different level of effectiveness when compared to the circulating type.

Here in the midwest where the cold is nothing compared to David's experience, we use the factory block heaters in our diesel tractors/farm trucks and they work fine for starting assistance.

Yes, I was saying 'i don't know' but if this type of block heater causes cracks, that's not good.

I can understand why a circulating heater would be better!

Anyway, I spotted these and thought it germane to the conversation...

I'm not sure what the factory ones cost, but $25 seems a good deal.

As Scott has already pointed out, there is a chart showing serial number breaks for changes made to the 6.9’s.


The problem is, it does not directly state anywhere “this is where we improved the casting around the block heater boss”. The following information is copy-pasted from another forum, but should help:

 6.9L and 7.3L Core Identification

6.9L Old Style Block

Block Casting Number:

On left side of block (beneath oil cooler) 1805440C1
Note: Some 440 blocks are truly new style and must be visually inspected by raised donut around the block heater, frost plug (right rear). Old style below serial number 173828.
Visual Identification: *No counter bored area for block heater
*No defined area on side of block for dip stick
*Thickness of cast iron around block heater 3/8" (.375")
Head Bolts: *7/16, 12 point socket is used to torque head bolts
*Block tapped with 7/16-14 for head bolts

6.9L New Style Block

Block Casting Number: 1807996C1 Note: Some new style blocks have casting
number 440. Above serial number 173828.
Visual Identification: *Has counterbored area for block heater
*Very defined relief area cast in side of block for dip stick tube.
*Thickness of cast iron around block heater 15/32" (.470")
*Latest style (not all new style 6.9) has ribs around head bolts, rear two on left side go from head gasket surface to pan rail - same as 7.3
Head Bolts: *Same as old style 6.9

7.3L Block

Block Casting Number: 1809000 C1
Visual Identification: *Same as 6.9L new style block
*Head bolt ribs on side of block extend from pan rail to head gasket surface or rear two head bolts left side
Head Bolts: *1/2" - 12 point socket is used to torque head bolts
*Block tapped with 1/2 - 13 for head bolts

My understanding is that the problem blocks (for block heater cracking) were found in 1983 and very early 1984 trucks. Mine was a 1986 so I brushed it off and used my block heater all the time. Later I discovered the engine was not original, and mine was a very early s/n. Oooops.

I have read if you use a block heater on an early 6.9 that you should consider plugging it in while the engine is still warm. I have also read that you might want to consider a lower wattage heater (they are available in several wattages). I have seen the radiator hose heaters, but I have no idea how they work on a 6.9 without a pump to circulate it through the block. I do know that the stock block heaters work very well. There is nothing like an easy start plus instant warm air out of the vents when it is below zero outside 🥶.

One more thought... if your glow plugs are working yet you are having difficulty starting, it could be your starter isn’t turning the engine over fast enough. This could be weak batteries, poor cable connections, or a weak starter motor. The decline can be gradual so that you don’t notice it, and in cold weather it does not have to turn all that much slower than normal to give you starting problems. I have thought mine was cranking just fine (but no start) and after cleaning the cable terminals and grounds it would fire right up. If I remember right Ford said the 6.9 should start on glow plugs alone down to around 10*F and some owners brag that theirs will start on only GP’s in below zero weather. I prefer the block heater whenever electricity is available, but it shouldn’t be a requirement unless the temps are very low...

Steve, That's a good point about the hose heater, and I might end up doing that. As you said, the plug doesn't leak now, so it might be worth bypassing the risk altogether.

Ford F384, thank you for the detailed answer. I think that may be the culprit to the hard starts. I've cleaned the cable connections pretty thoroughly and the batteries are only a year old, but I have no idea about the age of the starter. Temps here get to maybe 10-20 at worst overnight, so the motor should fire right up without even having to use a block heater, which would eliminate that problem for me. I'll check on the starter (for all I know it's original), and if I end up going with a new one or something along that route, I'll update the thread.

Thank y'all very much for the details responses and help, I appreciate it a ton

I like the block heater even if your low’s are still within GP starting. It just ‘feels’ like you are being nicer to the engine, and gives you peace of mind that it’s not going to give you a hard time especially if it’s your only transportation. If you have the later block, I wouldn’t hesitate to use the stock heater.

If you do end up wanting a starter here's one for $85 delivered (no core)
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F174487849329

Again, these may be rebuilds, but I can assure you anything with UHR is completely refurbished.
Their business depended on Ford trucks and vans 30 years ago and downtime meant lost profits.

They also have NOS Motorcraft starter cable assembly's for these solenoid style starters.

To anyone else.... there's a whole lot of 460, 6.9 & 7.3 parts there.
But you're going to be searching through tens of thousands of parts.

Jim, thanks for the link  Looks like a great option

Several good points have been brought up here already.  Prior to purchasing my truck i did come across that cracking issue from the oem block heater.  I cant recall for sure the years but i think the 85 was one of them, something to do with a weak point in the casting (i think).  

Definitely have to start with the starting system.  Clean terminals on both battery's.  The oem alternator is 65 amps (i believe).  I doubt this is enough to keep the batteries topped up over time.  I regularly disconnect the batteries (just the grounds) and charge each battery separately using a 1 amp noco smart charger. Slow charging is best for these batteries.

These engines are famous for air intrusion also.  The return system is common for leaking.  Return kits are available and not very expensive or hard to install.  I have a schrader valve by my fuel filter.  If yours does, depress it prior to start.  You should get a small shot of diesel.  If not it will take some cranking to purge the air out and bring up fuel pressure (could be a sign of the fuel system leaking down). It says you replaced the injection pump, did you time it after?  Incorrect timing will give you hard starting as well.

Test the glow plugs using an ohm meter (or DVOM).  Testing with a test light will not give you a good result of the condition of the plug, just shows working or not working. Test if the system is actually supplying power to the glow plugs when the key is turned on (check both banks).  Many recommend Motorcraft plugs and that is what i used as well.  Other brands may swell when burnt and you dont want to deal with trying to remove those from the head.  My controller stuck on and burnt my motorcraft plugs, zero swelling.  I converted my system to manual after that and recommend others do it.  Cold start, you should get about 10 seconds of glow plugs.

I currently have 3 engine heaters on mine and about to add a 4th.  
The factory block heater - I use this only when I need the truck quicker due to the cracking possibility.  
Lower rad hose heater - doesn't work really great and is likely due to not being mounted low enough in the system.
Oil pan heater - silicone electric pad mounted to the bottom of the oil pan.  Installed because I keep 15W40 in it year round.  Works great to warm up the oil. Once the oil warms it will start to radiate up and warm the engine as well.  I bought a low wattage one though - i think 125 watts, so that would take awhile.  
When all 3 are plugged in - warms the entire engine nicely.  

I am hoping to get away from the rad hose heater and block heater.  I have purchased a circulating block heater.  Most are 1500 watts and that is a full line load for most outlets.  Chances of tripping a breaker are much higher.  I found one that was 850 watts and plan to install in the near future (not looking forward to seeing if I can get the block drain plug out - after 35 years of being in there).  There is no pump in these type so it needs to mounted very low - thermosiphon technology.  So i will use this and the oil pan heater.  
I start it in low temps such as -30C (-22F)

All of my fuel is treated with Alliant Power - ultraguard.  It improves the cold filter plug point for winter temperatures.  

Some lab tests show better results then Stanadyne (likely a very good product as well).  

6.9-250, thank you for the detailed answer. Battery's are new and the terminals are good/tight, though I might start to slow charge them as it gets colder.

Glow plugs are good as well, no air leaks, and the IP was timed. I'm thinking of installing a manual bypass at some point.

Still have to figure out if my block is a pre-block heater fix casting until I use the heater.

However, just as an update to the thread and to anyone who might have the same problem I had with hard starts:

I took out the old starter and put a new gear reduction one in over the weekend (a Nippondenso - part # 16658N - https://www.qualitypowerauto.com/catalog.php?item=35). That top bolt was a PITA to get out, but feeling around with my left hand and using a 10 inch extension for my socket wrench in the right finally got it out. This new starter is a BEAST. I can hear and feel it turning the motor over much faster than the old starter (which I believe was original), and the truck starts right up now, even after sitting overnight.

Of course, I still have to see if it starts as easy when it gets really cold and the truck's outside (I've had it in the garage). I'll probably end up plugging in the heater just to make it easier on the motor and/or getting a circulating block heater, as many have recommended, which is probably the best option in terms of longevity. If I end up going that route, I'll update this thread for the sake of whoever might find it helpful.

Thank you all again for the great advice. The hard-start/cold-start problem seems to be solved for now.