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1979 Mark V Overheating Issues

Hi Bill –
Thanks so much for your time. Quickly about myself. I’m ASE and I-CAR certified in many areas. I own and run a small business in classic car restoration named ‘Take It To Hart’. Auto repair and restoration has been my passion for well over 35 years. I eat, sleep, dream and at times bleed oil.
Much of the comprehensive work you will read isn’t just due my dilemma. Moreso, this is just the way I tend vehicles and/or provide maintenance.
The vehicle: In using the ‘Condition Rating System’, I’d rate my Mark V continental as category 2. No real restoration has ever been needed. Other than belts, tires, carb., etc., things remain original and intact. This Mark was issued an appraisal several years back of over $12,000.
I am the second owner of this ’79 Mark, with only 59xxx original miles. I know the original owners quit well. The Mark looks fantastic, rides and preforms just as fine as she purrs.
Over the last month; motor/trans. cleaned and detailed. Oil/filter, trans. fluid is either fresh or at manufactures acceptable range/viscosity/life expectancy…
Tune-up: new is/are the control mod., coil pack, resistor, cap, rotor, alt., wires and plugs. All air filters too have been replaced along with the snorkel tube and the likes.
Cooling system (no kinks) new: radiator just before I purchased made purchase, cap (16lb.) water pump and gasket, coolant; correct type correct with the correct mix balance, coolant hoses and clamps, second thermostat and gasket, all vacuum lines and a number of vacuum/sending units, (water valve and the like are operating as designed).
The A/C is 134a. I only operate the a/c for liberating itself. I want to recall the car having an air pump for emissions. I also want to recall not having a belt installed. If this is correct then the car has been this way prior my ownership, and long before any overheating / boil over issues. All other belts replaced and adjusted to the correct tension specs. Shroud is fully intact and without flaw. The fan too is undamaged. (I don’t see, nor can I find any info. on-line as to a clutch like drive to the cooling fan. I want to recall however that when I replaced the water pump there was only a very small coil spring. Hum, maybe not. At present I would have to say the fan is directly driven off the crank.
Last week when I replaced the coolant hoses, I took off the heater core cover cap. There wasn’t debris inside the case. All was resealed at re-assembly.
I haven’t any fluids mixing together, nor do I blow smoke from the tail pipe at any point in time. No kinks and/or obstructions in the exhaust lines/pipes. I could stand to tighten the exhaust manifold to tail pipe a bit.
Am I missing something? Lord, I don’t want to hear heads, or block in your reply…. just kidding on this last part. I can’t tell you how appreciated any food for thought would be at present. A mere and measly 4xxxx mile is all I’ve been able to put on the vehicle since ownership. For over 6 years it’s been one thing following another. Literally. The prior owner has no recall to overheating. They are even older school then I, and only provided service when something broke. Today I’ll install a back flush. Old school thing for me be this un/necessary.
Again, many thanks!
Suffering from the Queen Mary blues
Darrell –
For your overheating issue I need to ask you a couple of important questions before replying. Does the overheating occur at a steady highway speed or is it during times of idling or in heavy hot traffic? When the overheating begins do you notice the Hot engine light is on or do you only notice Boiling over and steam etc. from the engine?
Wow, Bill, what a quick reply. I was only hoping to have such a turn around time. I’d be happy to send you pixs of the Mark if interested. Thanks also for your compliments on my tending her and her needs. Most importantly, I’ve very excited to be a part of the group. I hope that in some way I can make my own contribution.
I’ll be short and brief at this hour. As for your questions…
1. Does the overheating occur at a steady highway speed or is it during times of idling or in heavy hot traffic? The actual spew/boil over is when the car is shot off. I’m unsure if I’m spilling during idle. As you could imagine, I don’t want to be idle when I’ve begun to smell the coolant, so, I’ll slow up so I don’t have to stop. During these conditions I do most anything to be making my way home. I’ve had this car towed 5 plus times as I was just too far from home. I’d hate to do any permanent damage. This car isn’t new so a limp hope is more less out of the question.
2. When the overheating begins do you notice the Hot engine light is on or do you only notice Boiling over and steam etc. from the engine? I’ve learned to keep an eye on the instrument panel light but am always disappointed. The light lights, but never during the moments I’d expect it to. When the ignition is turned off, after about or around 1 minute, I begin to hear the boiling from the overflow can. I keep the hood closed as not to damage the paint. Once i know any possibility of spewing is over, I allow the hood open for a quicker cool down.
I hope I’ve answered your questions, Bill. So, in other words, I’ve not really allowed the car idle when on the road to know if spew, boil, boil over would occur if idle. I’ve NEVER noticed the instrument panel light on during any time I’d think it should be on. When cranking for motor start, the light in fact lights.
I’ll attach one of my most fav. pixs of the Mark. It was taken a year or so back. Even then I was having issue.
Regards, and again, thanks so much Bill.
PS, I hope you enjoy the pixs I’ve attached.
mk v.jpg
Hi Darrell –
From your description of the parts that were replaced to correct the overheating and loss of coolant it appears that you have covered all of the bases . I also notice that you state that the radiator was replaced prior to your purchase of the vehicle. This suggests that someone was addressing an overheating or a loss of coolant issue at that time. Since you don’t say if anyone has tried to diagnose the problem when it occurs and I am not there of course at the time I will give you a “laundry list” of possibilities for you or your mechanic to consider. These suggestions are based on our experiences at Lincoln Land with these conditions.
Coolant strength may be too weak
The thermostat could be installed upside down
The rad. cap could be incorrect or defective.
Engine timing could be incorrect.
The cooling flex fan could be installed backwards ( these 400 cid engines had a 5 blade – 18 ½ inch diameter blade )
The radiator ( even if new or newly re-cored ) could be incorrect, faulty or woefully undersized.
Internal engine gasket problems
As I stated above Darrell these are only suggestions and possibilities. In cases such as this we sometimes need to backtrack and carefully consider that there may be problems with some of the work that was previously performed. If all of the above is “correct” in all respects then and only then the engine should be inspected by a good known engine technician for an internal problem. I do hope that this helps you and turns out to be an easy repair.

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