Runaway heat, hard starting, rough idle and etc

[Wixomhead]

71 460 was running fine when pass exh manifold finally cracked, see other post if you really want to . Also - temp gauge consistently ran dead center, but this spring it would sometimes creep JUST A SMIDGE to the right of center, but that's all, ever.

Anyhoo - I snapped 3 bolts removing the exh manifold, fun stuff.

So I elected to remove both heads; did a home valve grind while they were out (boy those valves were filthy but SNUG in their guides).
Put everything back together, no surprises. Paid usual special att to china wall no cork, but RTV black 1/4" bead and corners intake gasket joints.
Water pump, radiator untouched. I replaced the 195 thermo with a 180 for fun. Car ran perfect for a few hundred miles, but interestingly, no cooler....

After 500 miles, car has slowly developed some very bad habits and getting worse now:

Idles 650ish OK but slight missing - idle quality 8 on a scale of 10 (perfect). Sounds like missing at each exhaust tip cold or warm.
Stumbles BAD and hesitates on accel, in park OR under cruise. Almost like a massive vac leak, but see below.
Best vacuum reading I can get by messing with timing (10 BTCS) and idle mix screws (out 3 turns) is 17-18 inches.
Heat gradually climbs past the "P" on the temp gauge, regardless at idle or cruising at 45
All eight plugs look the same and are gapped at 34
Oil remains crystal clean, good enough to sip on ice...
I am well aware of the reverse head gasket risk; I'm almost certain I installed them properly ... both 3" gasket tabs are exposed at both front, tops of heads
Lower radiator hose approx 2- deg cooler than upper

About ready to pull the intake and tear back down. Where/what else should I be looking at? Advice?








NOTE: Why the paint discoloration around all four pass exhaust ports?

[action]

The paint is discolored around the the exhaust ports because it is hot there.

The 180 stat will not make the system run cooler. If the coolant gets to 200 degrees both t-stats are open. The job of a t-stat isn't to cool down the engine, It is to heat up the coolant as fast as possible to a pre-determined temp. Beyond that a working T-stat is wide open and is no longer in the picture.

With that said seems like you have a cooling system issue. Likely you have found it in the radiator. A 2 degree change in temp from top to bottom is NOT good. Should be more than that. Way more!
Restricted radiator - either internally or externally and/or .....
Debris in the block
Water pump that is not moving as much coolant as it used to

The vacuum is a bit low. Is the vacuum steady at 17 to 18?
If yes, warm up engine, snap open throttle and close. What happens to vacuum reading then?
Recheck torque on intake bolts

Any spark knock or pinging?

Action

[Wixomhead]

Thanks much, Action.

Thermo function explanation much appreciated, that makes sense.

Sorry - I meant to type temp diff between rad hoses is indeed 20 degrees, not 2.

And exh ports - pass side is discolored as you can see, but driver side - much less so. Thought it might mean something.

Vac is 18, steady. No knock/pinging, even at heavy accel up hills.

I torqued intake (and heads) by the book. I didn't recheck all 16 intake bolts but a quick check of the 8 bolts at each corner shows they are indeed tight.

I stuffed paper towels town 8 intake ports and 4 coolant passages during assembly. Possible I missed removing one in the coolant passage, but wouldn't expect paper towel to last long in 200 degree coolant?

Rad cap off, engine warmed up to temp...I can see level of water in the rad tank drop a good 3 or more inches when throttle is applied. But I'm not seeing a lot of new coolant flowing in from the top row of fins to replace it, more like a trickle. This seems odd, but given the temp diff across hoses I wasn't giving it too much thought.

[Mike]

If you missed a paper towel you might have found part of the problem. It won't disintegrate. If it breaks down it turns to mush like wet toilet paper and drops further in or moves thru the cooling system.
When you get off throttle does the rad fill back up to normal level quickly?

[action]

Doing a vac reading snap the throttle and then let go.
Should drop to near zero, then up to 25 or so and then back down to the start point.
Which would be 18. While that is considered acceptable, I find it a bit low as in the engine isn't that healthy.
Do you have a vac reading before the work? If so post back
How many miles on the engine?
Popping the right valve cover and checking that both valves are fully closed at TDC might be worth checking. You are looking for a timing chain issue. The vacuum reading doesn't seem low enough for that. With the base ignition timing set to spec what is the vacuum reading?
Not sure what the spec for base ignition advance. You said at 10 BTDC the vacuum is 18. If you advance more does the vacuum increase? Say to 15 degrees BTDC. (Leaving it there you will have hard start on hot engine)


I would think a paper towel would cause considerable more issues in creating over heating.
After the coolant is cold is the level the same as before a heat cycle started?
You might be working some air out.
A 20 degree drop is better than 2 for a warmed up engine. But won't work on a hot day, under load with AC on. Likely the drop under those conditions will need to be double that to prevent over heating.
What is the temp going back into the engine?
What is the temp on either side of the T-stat?


I can not help but think the low vacuum reading and elevated cooling system temps maybe related

Action

[TonyC]

The problem could be more ingrained than almost anyone suggested. Yes, if you missed a shop towel in a coolant passage, that will be a problem. Also, if you've never removed the coolant drain plugs in your engine block, that will explain your underlying overheat problems. Nobody ever thinks about draining the block when they address a cooling system. Heck, even I was guilty of that until very recently. Take out the drain plugs, on both sides of the block, then run the most pressurized water you can through it. Hint: If nothing comes out of the block when you take the plugs out, or if coolant just trickles out, you've found your clogs and the cause of your problems. I suggest getting a strong, small-head magnetic probe to go into the block's coolant orifices, to bust up and fish out the rusty debris that doesn't immediately flush out.

---Tony

[Wixomhead]

Mike: YES, with rad cap off and engine operating temp, water level dips then rises right back up to top after throttle.

Action TonyC:

I cranked timing all the way to 12 where I heard slight ping on accel under load then backed off again to 10. Car has been at 10 BTDC since forever, no issues...
And: See vacuum test video. I may have found stumbling problem - note accel pump not doing much pumping - when hit, I see some fuel squirt but def not a strong stream.

https://youtu.be/nmYmgPg1yf4



PS: Why can't I embed video code?

[youtube]<iframe width="560" height="315" src="https://www.youtube.com/embed/nmYmgPg1yf4?controls=0" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>[/youtube]

[TonyC]

Okay, that has to be needed diagnosis. But it still won't address the heat buildup. What about the condition of the coolant in the block? Have you drained that yet?

---Tony

[action]

What about the condition of the coolant in the block? Have you drained that yet?

---Tony

Likely brand new. In the first post the OP stated he removed the heads due to a manifold crack and fastener mishap. Then replaced the thermostat.
I suppose reusing the coolant is possible in that scenario. Just not likely

However the answer to the second question is yes.

Action

[Wixomhead]

Hi folks - thanks again for all the quick replies and help. Did I mention the car has 100K on it, I bought it with 84K from orig fam and I could tell it was definitely well maintained but it also sat a lot (indoors).

@Tonyc: No, I never pulled the freeze plugs out of the block. Per earlier posts, with heads off I there was a million things I could inspect and replace (cam, water pump, flexplate (some worn teeth), timing chain etc) but I drew the line early - it's June, prefer to do that stuff in November...may end up doing freeze plugs after all - let's see: updates:

* The hard starting and stumbling is clearly from the accelerator pump 'stickiness'. The Autolite 4300 is only 4 years old, bought from Rockauto. I disassembled, found some silt in the bowls, confirmed correct float level (13/16") but the accel pump still not working properly. Ordered a rebuild kit which comes with new pump/plunger cup thing.

* I reserved and re used the coolant from when I drained the block to remove the heads 2 months ago. This coolant was only a couple years old/few thousand miles and a bright shade of green before the head R&R.

* Just drained the coolant again last night and removed the radiator. The coolant clearly had more brown tint this time...I would not classify it as filthy but I am going to refill with brand new 50/50 and distilled.

* I just dropped the rad off at local shop for test/flush/etc and they promised to get back to me tomorrow with info. Forgot to bring them the fan to inspect for me, there is soft crud all over the front of the clutch - fan only spins free 1/4 to 3/4 turns at most when hot or cold, respectively. Again - car gets hot in idle or highway speeds, no diff.

* I ordered a $28 infrared thermo gun from Amazon/be here in a few days. If necessary, hope to use this to isolate hot spots in specific areas of the motor for diagnosis. Now that I think about this, I don't think I ever even put paper towels in the heads...no need - I removed them right after the intake and cleaned/sanded the mating surfaces all on the bench. I'm was also in the middle of a top down removal of another 460 (another story) and for sure I blocked the passages on that engine, which is now back and running fine.

QUESTION: Does anyone run more than the fuel filter on the carb? I was concerned about the amount of debris in the bowl - should their be another filter somewhere that I am not aware of?

[tomo]

I would check the Shop Manual for the idle and timing settings and set them up as described in the manual. The timing setting could be part of the cause of your overheating.

Idle mixture screws turned out 3 turns sounds excessive to me and could be a cause of the low vacuum, but will have no effect on the overheating. Most carburetors have the mixture screws open 1 1/2 - 2 turns.

The idle speed also seems high to me. I would expect 500-550 rpm to be closer to the factory specification. This can also affect the vacuum readings and the initial timing.

While you are waiting for the radiator, I would recheck the valve lash to make sure that all of the valves are opening. I would also do a compression check. If the readings vary more than 5% between cylinders, also do a wet test with a few squirts of oil in the cylinders. Next I would check that the vibration damper hasn't slipped and that TDC agrees with both valves closed on cyl 1.

One fuel filter should be sufficient to remove troublesome debris. If your tank is rusty inside or the fuel line has started to rust inside, you should repair these as soon as possible because the rust could lead to more serious problems. I would check them out for the cause of debris in the carburetor.

The current blend of gasoline sold is very clean when dispensed. It can cause rust in the tank and steel lines because of the corrosive nature of the oxegenators added to reduce air pollution. I like to add Seafoam to every fill up and use Stabil 360 or Marine, when the car is not going to be driven regularly in the hopes that they will keep the corrosion to a minimum.

[action]

As long as the cooling system is open and you found some brown, get the garden hose and see if you can blow some fresh water through the block to remove any debris. The best time to do this is just before you put it back together. Fresh water left in the block will cause bare metal to start the rusting process. At least the old coolant has some anti-rusting chemical in it

And I agree with Tom on the ignition and fuel settings

Action

[TonyC]

Sorry, but I still feel I need to stress my suggestion, especially since it appears that Action feels similarly. If you still have rusty discoloration between flushes, that tells me the block needs flushing, which cannot be done by "standard" flush procedures. The sediment that settles in the block gets lodged in and will not go anywhere unless it's directly attacked at the block. And after 50 years of use/abuse/neglect, it can have enough deposits inside to clog up half the coolant passages in the block. When the coolant's flow becomes that compromised, the oil has to take on added burden of heat removal, more than it's meant to, adding more to the heat problem. Even going so far as removing the heads will not clear it out if you don't go into the block itself. I know this for a fact from recent experience. Garden-hose flushing may not be sufficient, although still doable; if you have access to a pressure washer, I recommend that. Plus, keep some magnetic probes handy; you will need them to drag stubborn deposits out even with a pressure washer. You will certainly require them if all you have is the garden hose.

That established, I also need to clarify the difference between freeze plugs and drain plugs. Freeze plugs aren't meant to come out except for block repairs; and if there is no sign of leakage around them, it's best to leave them be. Drain plugs, on the other hand, are meant to be removed with regular tools, sockets or Allens or the like, and reinstalled with hardly an issue. It's the drain plugs, not the freeze plugs, that I'm advising to remove. That will give you an idea of just how much rusty crud you still have to get out of the block, and thus out of the system. Clearing the radiator, heater core, intake, heads, et-al is smart, yes, but not complete if the block itself is not addressed.

As for the fan clutch, I inferred that you see clutch oil on it...? If it's been a while since you replaced that clutch, I recommend doing that as well.

---Tony

[tomo]

Tony, your experience with crud in the block is very common. It should be cleaned out, but it is difficult to remove the crud with the engine assembled. A reverse flush will remove the loose stuff.

The OP said that the engine ran at normal temperatures before the exhaust manifold and the valve job and even ran at normal temperatures for about 500 miles after the work was done. This leads me to believe that the crud in the block is not the reason for overheating. The rust in the coolant could have been loosened from the walls of the block by the overheating condition. This leads me to think that some condition has made an abrupt change.

Overheating can be caused by plugged radiator, crud in the block, timing, and a lean mixture. Sticking or maladjusted valves can also cause a rise in operating temperature. My guess would be that the valve lash might have changed after run in or that the head bolts need to be re-torqued.

[TonyC]

It could still be the reason, Tom. I ran for 16 years with only sporadic overheat issues which seemingly were resolved with the typical services. But meanwhile half the block's coolant passages were still clogged, which must have contributed at least partially to the holes in the sides of the pistons and that crack between the #2 and #3 cylinders. It could be that some crud in the OP's engine occasionally comes loose to clog other things, but there's still so much in the block that the problems will linger on and reoccur unless it's all removed directly...which means, of course, the "nuclear option" as you correctly indicated.

---Tony