Overheated - Now starts hard, runs rough

[Boomvang]

Well I guess I get to join the dummy club. My 1984 351 PCM (no elec ignition) got overheated the other day. When I realized it I idled back to the dock. I found a leak in the hose to the water pump (hence no water leaking when I checked).

The motor didn't seize, it ran fine idling back to the dock. When I got home and it cooled down, I started it briefly, seemed ok. The next day I changed all my hoses, new impeller (old one was destroyed). Now the motor is very difficult to start. Cranks like crazy, acts like it wants to start but can't "catch". Then when it does start, it runs very rough for a minute or two and then dies (like it's not getting enough gas).

One oddity - took off the distributor cap, cleaned up points and rotor, put cap back on and it wouldn't even TRY to start. Took the cap off, confirmed that I had put the rotor back on (I had), put the cap back on and it immediately changed back to the earlier symptoms of (hard starting, stalling). Seems to indicate that the distributor is somehow involved?

Sorry for such a long post. Thanks in advance for help.

Steve

[pistnbroke]

Compression test to see if you have buggered the bores

Clearly you did not seat the dissy cap properly .....forget that go with what goes wrong when you over heat it ...????

[PAR]

Sounds like a head gasket(s).

[Boomvang]

I was thinking (fearing) head gasket as well. I drained the oil today and was happy to see...just oil, no water.

Am I correct in thinking that rules out head gasket?

[Frosty]

No --the head gasket could have blown into the water, actually could have been the reason for overheating. Fit 2 new gaskets, plugs ,oil and thermostat.

[pistnbroke]

may have blown between cylinders which is common .. or between cylinder and water gallery then the pressure stops the water circulating ....only water in oil if the leak is between oil and water gallery ..at least you have not buggered the bearings !!!

get the head off ...

[PAR]

Diagnose properly first, before you start ordering parts. There are several test you can do, try a leak down test first.

[Frosty]

A leakdown test will show that, but thats expensive equipment.

A top end gaskets set is what 20 dollars and 4 hours work?

[CDK]

A blazing hot engine and just a few splashes of cold water from a damaged pump, that's a recipe for expensive trouble. Pistnbroke's gasket, blown between the middle cylinders is very likely, so is Frosty's leak to the cooling circuit.

But there may also be cracks in the head itself, where cold water hit the metal. And the risers will have suffered, together with the hoses attached to it.
The engine is 25 years old: this may be the moment for a complete overhaul.

[gonzo]

You can buy a compression tester for about 25 buck. They are not professional grade but will do. It would seem odd that the head gaskets on both sides are so bad that it won't even fire. Check the sparkplugs. Sometimes in an overheat the oil thins out and fouls the plugs. Changins parts without troubleshooting first is stupid. You end up not knowing what caused the problem.

[Frosty]

He did'nt say a compression tester he said a leak down tester.

Its just 2 head gaskets. I could have done it by now.

It does run Gonzo but runs rough.

[PAR]

A compression tester will work too. Clearly the poster is in over his head or would have sorted out the symptoms by now.

[Frosty]

A compression tester tells you what your compressions are . A leak down test puts in air from a compressor and gives you a % reading of leakage,then if you listen to exhaust, intake, crank case or radiator you can see where its leaking to. Totally different machine one is expensive the other is not.

[gonzo]

A leak down tester at Harbor Freight is selling for about $70.00. That is not so expensive. I don't think that you can see where it leaks in a gasket with a leak down tester. The air will go from the combustion chamber into the engine.
The engine is not running, it only cranks

[mydauphin]

Pull the plugs see if it turn over easily. But chances are your are going to have to pull heads... You may have damaged bearings...

[Frosty]

When doing a leak down test you are supposed to lock the engine or it will move--very quickly and can be dangerous. You would normally lock at TDC. If your gauge showed leakage beyond what should be normal it would /could be going to the next cylinder where it would have a valve open.

Iether way the head gasket has gone.

[Boomvang]

Thanks to everyone for the input. For the record, most input seemed to indicate that no water in the oil meant probably no head gasket issue. Shop suggested that the inside of the exhaust tubes had blistered and was cutting off the exhaust. (said they see this frequently). I checked and the exhaust tubes were fine.

They also mentioned a slight chance of fried condensor. Put in new condensor (as well as cap and rotor). VAROOOOOOOOOM! Wow, what a relief. I'm back in the saddle.

My sincere thanks to those who took time to respond.

Steve

[Frosty]

You know theres lots of threads like this.

The owner knowing nothing buggers up something by checking it out.

The experts!! not even contemplating damaging a cap and a condenser doesn't put that into the equation.

Ive never see a fried condenser and I would have thought that was electronic anyway??? But to fry a condenser way up in the distributor without damaging any engine components????? still not right.

I don't think you overheated it in the first place.

[PAR]

I've burned up lots of condensers over the years, it's not hard to do.

Any respectable mechanic would have a diagnostic routine to preform, which would include all the "usual suspects", normally this encompasses the ignition parts too. At least my routine does.

[Frosty]

I cant Imagine how on earth you fry up a condenser. Replace then yes fry No.

But if he brought it into your shop and said Ive overheated the engine you would'nt look at the condenser and see if the dizzy cap was seated --or would you.

How do you do a routine on the internet?

As I say I dont think it was overheated, some guy on the slip with his hands in his pockets said "Oh youve probably overheated it"

[Boomvang]

Dear Frosty,

I'm sure you're a fine chap and we'd enjoy a cold one together...in fact, I'll buy. Can't help but mention that your comments do come across, a bit...well...Frosty. Perhaps that's why you chose the name. I actually did the things mentioned on this forum first.

The owner knowing nothing buggers up something by checking it out.
-While I'm sure I can't match your level of expertise I wouldn't say I "know nothing". Kind of a leap on your part, wouldn't you say. ;) I'm not sure why you think I "buggered something".

The experts!! not even contemplating damaging a cap and a condenser doesn't put that into the equation.
- I changed the condenser because my local shop suggested that they have seen them go bad on an overheat. I, like you, would not have thought of this. I'm quite sure that I damaged neither the cap or the condenser, however the shop had stripped one of the hold down screws a couple years ago and I wondered if lack of proper seal had allowed oxidation (a bit of grasping at straws, I'll admit). I basically changed the cap (and rotor) because I bought a tune up kit and it was easy to do while I was swapping the condenser.

Ive never see a fried condenser and I would have thought that was electronic anyway??? But to fry a condenser way up in the distributor without damaging any engine components????? still not right.

- I have the same question as you. Since the "fix" came when I changed cap, rotor and condenser, I can't be sure which was the actual culprit. I thought about swapping back to find out, but I don't think I will. As I have stated, I did clean up the (1 year old) cap and rotor, so I'd be surprised if they were the problem.

I don't think you overheated it in the first place.

- I can only chuckle at the pomposity of this remark. Maybe if you had seen the temp gauge, the smoke, the discoloration of the valve covers and the melted plastic shield covering the solenoid, you would feel differently. Alternatively, if you questioned that it really overheated, you could have asked why I thought that.

As I mentioned in my original post, I used my basic engineering problem solving to deduce that the problem was somehow associated with something under the distributor cap, since a simple removal, clean up and reassy changed the symptoms so radically.

Thanks again for your input, and I hope I can look forward to your expertise in the future. Guys like you who take time to share your knowledge on forums like this are much appreciated.

[Frosty]

Maybe if you had seen the temp gauge, the smoke, the discoloration of the valve covers and the melted plastic shield covering the solenoid, you would feel differently. Alternatively, if you questioned that it really overheated, you could have asked why I thought that.
.

Boom Thanks for your Post , very nice, Shame it was'nt that long on the diagnosis and included that bit,-- but never mind.

yes Im a bit short, thats me.

Yes you can buy me a beer, and Im sure we would get on fine once you got used to the short bit.

I will take your advice and next time I will ask "why do you think you over heated it". The loose cap would have been moving about as the rotor arm turned. its not so much being water tight.

Oh well--watch that temp gauge!!

I assume you found what overheated it in the first place?

[Boomvang]

Thanks for the kind response. Yes, I could have included more info. When asking for help, I try to balance between enough info and making it too long.

As to the "loose cap" being the problem, I don't think so, and here's why. I mentioned that one of the hold downs is stripped. Now that I think about it, it's been that way for at least a couple years. I just snug it down as much as I can and attach the spring clip and it's been good to go.

In addition to this:

1. When I was having problems, I pushed down on the cap while trying to start to see if I was having any issue with the cap moving...no change.

2. I replaced the dissy cap but the stripped screw is still in the same condition that it has been for the last few years, and everything is fine. (It's actually the threaded portion of the dis assy that's stripped, I meant to get a tighten up on the protruding portion of the screw/bolt).

As to "what actually overheated"...it's still a mystery to me. As I said, I changed the condenser, rotor and cap at the same time and the difference was huge and immediate. Since I did it all at once (poor problem solving technique, but good way too finish when it's late at night), I can't be sure. Given that the shop suggested the condenser was fried, and they work almost exclusively on boats like mine. I'm going to go with that. Like you, I have a problem with this because from a heat transfer standpoint, there are a lot of things that suck heat and get way hotter than than the condenser got. Maybe they very are sensitive to temperature???

It's a mystery. But I prefer mysteries with gear that runs vs. gear that won't run.

thanks again,

Steve

[pistnbroke]

sorry I am with frosty ( again) condensers dont fry ..go open or short circuit but its more likley that the heel of the contact breaker wore away reducing the contact gap eventully to nothing on at least one cylinder and retarding the timing so it started to missfire..some of the newer versions of this old technology are thermoset plastic....