351C 2v overheat, rough idle - Thinking head gasket?

[LoveThatHood]

Good evening all,

1971 H code convertible w 351C 2v and FMX.

As a bit of background, I found this car a few weeks ago and the previous owner had it since 1989. During the time he owned it, it was driven less than 2500 miles, most of which was prior to 1992. So... when I got it it hadn't moved much. I took it out <5 miles when I put it in storage after buying it, and then drove ~50 miles last weekend. When I got back to storage, I noticed that it was idling a bit rougher and when i parked it, the radiator was draining fluid out the overflow. Never lit the idiot light in the dash (that I saw) , but I honestly don't trust lights because of experiences like this. Add to checklist...

Between work and weather, I didn't have much time to do anything to it, but did manage to get a thermostat, knowing that the cleveland had a history of getting the wrong one. When I swapped it out, I looked in the intake and saw the restrictor plate was in place, so I purchased the Napa THM 297 which was recommended somewhere on the forum, and also had comments about it being the right one for the cleveland. When I removed the other thermostat I did notice that the housing was pretty cruddy, so I cleaned it out as best I could with a screw driver but wondered if that isn't representative of other crud in the cooling system.

Anyway.. top off coolant. Go to fire up, and it was hard to start and when it did start, I had to keep some gas on it to keep it running because of a rough idle. Whenever I let off, it died. I didn't see any coolant or abnormal exhaust color, but it just didn't feel like it was firing on all cylinders. Pulled the distributor cap and looked at the rotor and points to make sure everything still looked OK and it did. Finally felt the top radiator hose and noticed it was hot and hard. Keep in mind that I only had it running for maybe 2 minutes, so I wouldn't think the thermostat would have even opened that much, but nonetheless, both top and bottom hoses were hard and radiator was quite pressurized and warm to the touch but not hot.

My suspicion is that I'm looking at a head gasket, but thought I'd see if any Cleveland or Ford wizards can chime in with other troubleshooting thoughts.

 

[vintageman]

Not sure if this will be the issue but the head gaskets can be put on backwards and prevent coolant flow. One of our members, David (Carolina_Mountain_Mustangs) found one of his had that issue on a car that he picked up and was causing overheating issues. Maybe try the Search function to see if you can find his posts on the subject because David has not been on much over the last few months. Good luck.

Tom

 

[351c1971]

My recommendation is to first use Radiator Clean & Flush to clean the system. Also run the heater during all tests to eliminate bypass issues. Is the water pump stock or aftermarket? Finally, with the radiator cap off, check for bubbles in the coolant.

 

[jpaz]

Pull some plugs to see if there’s any coolant on them. Running rough can be a number of things, vacuum leak, crapy gas, timing not set correctly or carb issues.
As for the coolant coming out the overflow, I have found that I can’t fill the radiator to the top, have to leave the level about 2” down from the top. I have a new stock radiator with the proper 195* Cleveland thermostat. No overheating problems at all.

 

[Sheriff41]

In addition to theabove, check if it has a fan clutch and make sure it is good.

 

[basstrix]

The first thing I'd do is pull the plugs, inspect them and if there's not an obvious problem, run a compression check.

What is the condition of the coolant? If the car was stored full of coolant since 1992, I can't imagine it won't have some major corrosion inside.

 

[351c1971]

You might also check the oil level. If it is creeping up, it is likely coolant leaking into the oil via the head gasket.

 

[LoveThatHood]

Thanks for all the troubleshooting ideas folks. I had family stuff today and didn't make it back to storage to look at it, but that is on my to-do for tomorrow morning. My thoughts

Remove rad cap and look for bubbles - that seems like the first and easiest place to go other than the fact that I can't keep it running long enough to get up there. I'll bring my daughter to see if she can keep it running while I look.

look at oil - I didn't see any indication of coolant or any fluid lighter than oil, but then again sometimes it is hard to see. I'll double check that too.

pull plugs and compression test - this was originally my next plan so I'll probably hit it soon too.

On coolant/water pump/etc - This is my first go-round with a Cleveland and first with a Ford in 25+ years, so a few behaviour questions - how quickly do you expect these to warm up? That was a big part of my concern is that in addition to high pressure, both the hoses were quite warm to the touch and radiator was hot enough I didn't leave my arm there. This was only after 2-3 minutes from the time I started, while feathering the gas to keep it at ~1000 rpm's. (guessing, as I don't have a tach yet) I don't think any of my GM 350's would even open the thermostat that quickly let alone get the rad warm, so I'm curious if it is common for these to warm up that quickly?

 

[351c1971]

You might also check the oil level. If it is creeping up, it is likely coolant leaking into the oil via the head gasket.

 

[351c1971]

Check if the water pump is aluminum. If so, the problem could be lack of bypass flow. If cast iron (stock) the bypass should be internal to the pump.

 

[Topless73Qcode4SPD]

Good evening all,

1971 H code convertible w 351C 2v and FMX.

As a bit of background, I found this car a few weeks ago and the previous owner had it since 1989. During the time he owned it, it was driven less than 2500 miles, most of which was prior to 1992. So... when I got it it hadn't moved much. I took it out <5 miles when I put it in storage after buying it, and then drove ~50 miles last weekend. When I got back to storage, I noticed that it was idling a bit rougher and when i parked it, the radiator was draining fluid out the overflow. Never lit the idiot light in the dash (that I saw) , but I honestly don't trust lights because of experiences like this. Add to checklist...

Between work and weather, I didn't have much time to do anything to it, but did manage to get a thermostat, knowing that the cleveland had a history of getting the wrong one. When I swapped it out, I looked in the intake and saw the restrictor plate was in place, so I purchased the Napa THM 297 which was recommended somewhere on the forum, and also had comments about it being the right one for the cleveland. When I removed the other thermostat I did notice that the housing was pretty cruddy, so I cleaned it out as best I could with a screw driver but wondered if that isn't representative of other crud in the cooling system.

Anyway.. top off coolant. Go to fire up, and it was hard to start and when it did start, I had to keep some gas on it to keep it running because of a rough idle. Whenever I let off, it died. I didn't see any coolant or abnormal exhaust color, but it just didn't feel like it was firing on all cylinders. Pulled the distributor cap and looked at the rotor and points to make sure everything still looked OK and it did. Finally felt the top radiator hose and noticed it was hot and hard. Keep in mind that I only had it running for maybe 2 minutes, so I wouldn't think the thermostat would have even opened that much, but nonetheless, both top and bottom hoses were hard and radiator was quite pressurized and warm to the touch but not hot.

My suspicion is that I'm looking at a head gasket, but thought I'd see if any Cleveland or Ford wizards can chime in with other troubleshooting thoughts.

Good evening all,

1971 H code convertible w 351C 2v and FMX.

As a bit of background, I found this car a few weeks ago and the previous owner had it since 1989. During the time he owned it, it was driven less than 2500 miles, most of which was prior to 1992. So... when I got it it hadn't moved much. I took it out <5 miles when I put it in storage after buying it, and then drove ~50 miles last weekend. When I got back to storage, I noticed that it was idling a bit rougher and when i parked it, the radiator was draining fluid out the overflow. Never lit the idiot light in the dash (that I saw) , but I honestly don't trust lights because of experiences like this. Add to checklist...

Between work and weather, I didn't have much time to do anything to it, but did manage to get a thermostat, knowing that the cleveland had a history of getting the wrong one. When I swapped it out, I looked in the intake and saw the restrictor plate was in place, so I purchased the Napa THM 297 which was recommended somewhere on the forum, and also had comments about it being the right one for the cleveland. When I removed the other thermostat I did notice that the housing was pretty cruddy, so I cleaned it out as best I could with a screw driver but wondered if that isn't representative of other crud in the cooling system.

Anyway.. top off coolant. Go to fire up, and it was hard to start and when it did start, I had to keep some gas on it to keep it running because of a rough idle. Whenever I let off, it died. I didn't see any coolant or abnormal exhaust color, but it just didn't feel like it was firing on all cylinders. Pulled the distributor cap and looked at the rotor and points to make sure everything still looked OK and it did. Finally felt the top radiator hose and noticed it was hot and hard. Keep in mind that I only had it running for maybe 2 minutes, so I wouldn't think the thermostat would have even opened that much, but nonetheless, both top and bottom hoses were hard and radiator was quite pressurized and warm to the touch but not hot.

My suspicion is that I'm looking at a head gasket, but thought I'd see if any Cleveland or Ford wizards can chime in with other troubleshooting thoughts.

Hi LoveThatHood,

I'm a believer in the keep it simple approach.
For a rough idle and engine dying symptom, a vacuum leak
is a strong candidate. Take a can of ether and spray it around
the base of your carburetor and intake manifold. If you get a
idle change then you have found the source of the vacuum leak.

Overheating.
I had a similar over heating problem.
One of the first things I did was change the thermostat.
Great improvement but my car still ran hot when sitting in traffic
so I started chasing other sources.
Replaced the water pump and fan clutch. Had my radiator cored and cleaned.
Added a expansion tank. All to no avail.
So let's start back at the beginning. I took out my new thermostat and
tested on a stovetop. The #$&% new thermostat was not only slow to open but
did not open all the way.
I put in a second thermostat and problem solved.
KISS...
Hope this helps...You'll figure it out eventually.

 

[mrgmhale]

The high pressure in the cooling system after only 2 minutes of running is a strong indication of a head gasket leak where combustion gas is getting into the cooling system. To make absolutely sure that is what is going on I suggest you go to a parts store and either purchase a Block Check kit, or rent/borrow one from the parts srore. They may charge you for the blue test liquid. To see how to use one you can loo at my YouTube video I did when showing how to use it on out 1973 Mach 1 (it did not have a cooling system issue, I just used it to show how to do the test, then showed what happens to the fluid;\'s blue color if it does detect combustion chamber.

https://www.youtube.com/watch?v=OhNQVEp7Kxw

 

[mrgmhale]

The high pressure in the cooling system after only 2 minutes of running is a strong indication of a head gasket leak where combustion gas is getting into the cooling system. To make absolutely sure that is what is going on I suggest you go to a parts store and either purchase a Block Check kit, or rent/borrow one from the parts srore. They may charge you for the blue test liquid. To see how to use one you can loo at my YouTube video I did when showing how to use it on out 1973 Mach 1 (it did not have a cooling system issue, I just used it to show how to do the test, then showed what happens to the fluid;\'s blue color if it does detect combustion chamber.

https://www.youtube.com/watch?v=OhNQVEp7Kxw

I neglected to mention that if you do end up replacing a leaking head gasket(s), or for some other reason end up having to drain out coolant, you should burp any trapped air in the engine before starting the engine. Otherwise the coolant in the engine that is present will end up getting far hotter than necessary before the thermostat eventually opens, as the trapped air in the engine will prevent coolant from reaching the thermostat's wax pellet enclosure. But burping (bleeding) air from the block initially you prevent having the thermostat from opening too late, and having alower level of coolant than desired. And, yes, of course I have a video showing how to do that also, at:

https://youtu.be/ESdDLBEUPU0

 

[LoveThatHood]

For those playing at home, here is.... "the rest of the story".

• Replaced antifreeze, thermostat, and radiator cap.
• I got the head gasket leak test kit and it didn't show anything. Stayed the same color, no yellow.
• Replaced distributor cap and rotor.
• Didn't have a compression tester handy, but looked at all the plugs and wires which all looked perfectly fine.
• Chased the few vacuum hoses I have and nothing felt cracked or out of place.

Finally gave in and decided that maybe there was just something in the carb that was gummed up that I hadn't found yet. As I was getting ready to pull the carb off I started taking photos to make sure I got everything back in place and noticed that there is a port on the back of the carb that would normally go to the brake booster, but since I have manual brakes it doesn't. However, it appeared to be open, and I found a hose that I assume runs down to the FMX transmission. Shoved it back on good and tight, fired it up and voila.... back to running smooth.

So - as called out by @Topless73Qcode4SPD - Keep It Simple Stupid. On the bright side, chasing down all this other stuff gave me a great opportunity to introduce myself to the 351C. Thanks everyone for your contributions to getting it back on the road!

 

[351c1971]

Could the port on the back of the carb be for the pcv hose?

For those playing at home, here is.... "the rest of the story".

• Replaced antifreeze, thermostat, and radiator cap.
• I got the head gasket leak test kit and it didn't show anything. Stayed the same color, no yellow.
• Replaced distributor cap and rotor.
• Didn't have a compression tester handy, but looked at all the plugs and wires which all looked perfectly fine.
• Chased the few vacuum hoses I have and nothing felt cracked or out of place.

Finally gave in and decided that maybe there was just something in the carb that was gummed up that I hadn't found yet. As I was getting ready to pull the carb off I started taking photos to make sure I got everything back in place and noticed that there is a port on the back of the carb that would normally go to the brake booster, but since I have manual brakes it doesn't. However, it appeared to be open, and I found a hose that I assume runs down to the FMX transmission. Shoved it back on good and tight, fired it up and voila.... back to running smooth.

So - as called out by @Topless73Qcode4SPD - Keep It Simple Stupid. On the bright side, chasing down all this other stuff gave me a great opportunity to introduce myself to the 351C. Thanks everyone for your contributions to getting it back on the road!

I also think the initial testing you did will be helpful in future troubleshooting efforts.

 

[AcesArneson]

You might also check the oil level. If it is creeping up, it is likely coolant leaking into the oil via the head gasket.

You could also just drain some oil from the pan, oil floats on water so if you have water in your oil you will find it in the lowest point of the pan.