Want really big car comfort but don’t like the gas bills? Ditch that giant gas hog V8 and replace it with a little six! That’s what the owner of this 1973 Mercury Marquis did, even though he lives in high-altitude Colorado and sometimes drives in the mountains, albeit a bit slowly. I came across his story at the Fordsix.com forum. His handle is Mr. Highlander, and I’m going to let him tell you all about this rather unusual engine swap:
I live in Denver, Colorado. I will start my story in September of 2022. I had a 1989 Lincoln Town Car that I was using as a daily driver. Some U-Haul truck tried to do a sudden U-turn in a busy street, and I was the victim that couldn’t stop. By the way, my friend and I were fine, the Luxo-Boat saved us. I always loved the soft mushy ride of these cars, and their sheer size. So I set out trying to find another one for a good deal.
I found a 1973 Mercury Marquis in Grand Junction (200 or so miles away) for $3,500 with 110,000 miles. It was a great car, smooth reliable (carburetor excepted). Until about a year and 27,000 miles later (July of ’23) and when the transmission pump seal failed, the engine blew a head gasket, and gas became more expensive. So in a complicated month long ordeal involving a dud 460, re-headgasketing the 429 (ended burning oil after, and blew the HG again), and torque converter seal replacement that didn’t work, I didn’t know what to do. So I sat and thought about. changing the engine. I needed something reliable, something with economy, and something with serviceability. Speed doesn’t really appeal to me as long as I can do 65 on the highway. I was going to look into an inline 6.
The Beginning:
I first needed to confirm it was going to fit with some modifications. After confirming the transmission cross member could be moved up to accommodate a C4 transmission, I set on the search for an inline. I was looking for the 240 or 300 engine. I checked on Facebook market place, and I found a 200 CID from a ’65 Mustang. It had only 40,000 Miles on it, and was selling for $1000. The seller had a C4 transmission out of the ‘stang too, but he sold it. So I found a C4 from a 81 Mustang with a CID in Laramie Wyoming, from a radiator shop, for only $350. It was described as “In working Condition”.
The engine seller was on the way down, so me and my friend (again, same one) picked them both up same day. I negotiated the engine down to $900, and the transmission down to $300. The cost of the negotiations were offset however, due to the fact that the bellhousing and torque converter would not bolt up. Ford decided to throw a wrench in the typical thinking process, and used a bigger pattern for 80-83. I ended up using a bellhousing and a remanufactured starter from a ’78 Fairmont, and a remanufactured TC. Also I replaced the TC seal and the slip yoke seal. I also had to get a custom Aluminum driveshaft. That was nowhere near cheap.
The Process:
First, I had to change the front coil springs. I wanted the same soft quishy ride. The OEM ones are rated at 470 Lb-per-inch. So I subtracted the 429 weight with the 200 weight. I got a difference of 270 Lb. I divided that by 2, (number of coil springs in the front), and got 135. I took that number off from 470 and got 335. So I had to find coil springs with a spring rate of 335 Lb-per-inch. After looking on Rock Auto, I found that Ford has one height and length of springs for their full sized cars. Compressed height is 12 inches, with a diameter of 4 inches. Only the rates change, depending on car. So by looking up a car an engine with a light engine (For example, 1972 Ford Custom with the 240 engine). They specified a spring rate of 318 without the heavy duty suspension. Close enough. A 240 is heavier than a 200, by quite a bit. But a Mercury Marquis is heavier than a Ford Custom (Longer wheelbase). So I thought it would compensate pretty well.
Next on the agenda was finding a transmission mount. Again, this was pretty straight forward. I just found a mount that was used in a full sized Ford with a C4. I am sure the old transmission mount would do, but it was baked after 50 years. Some sources say that C4 mounting hole distance and C6 mounting hole distance are different. I can confirm this is not true. They are the same. The only difference between the mounts is the height, which is different. The shift linkage was different between the two transmissions however. The column shift trannys had the lever facing down, and the console shift was facing up. I just used some scrap aluminum to make an adapter between the two. It also doubled in making a mount for the ICM.
The engine mounts were less straight forward. I had to experiment with these. I had a wild scheme about using 2 OEM 200CID Mustang mounts on each side. That didn’t work to make a long story short. So after that failure, I looked at what Chrysler was doing in their cars. What made me look at them, was that their motor mounts were simple. So I made 4 brackets, 2 for each side. It worked beautifully.
Performance:
I wanted (more like needed) to pep up the performance of the 200. The Load-O-Matic system seemed like a real boggy dog. So I kinda did the typical mod, and changed out the Autolite 1100 carb for a rebuilt RBS from a ’73/’74 Gran Torino w/ 250 engine. Modified the air cleaner so it would fit on the carb.
Also changed out the distributor out for a Duraspark II. To accommodate all the vacuum hose, had to use expensive fittings from Advanced Auto. I used the oil pressure switch from the 429. I like using the lights. (I had replaced it one time before so it was relatively new). More on the temperature switch later…
The exhaust manifold opening was pretty small at 1 3/4 inches. I wanted a little bit of more flow, So I got a 2 inch manifold off of EBay. I didn’t need the dual exhaust. Just something simple. I changed the thermostat and the housing. I wanted to make things simple, so that a 1.5 inch diameter hose was used across the car.
For the throttle cable, I bought one off Autozone, for a 1992-6 Ford F150/250. It was long, just what I needed. And it fit too! Amazing! Got to hand it to Ford for making it relatively simple. One thing that wasn’t was the PCV valve. I had to add one, because they had to use the crankcase down pipe.
Getting it started:
So it was time, after 2 months, after getting everything planned out, and installed (Suspension was a PITA, with replacing stuck ball joint and crusty rubber bushings). It was at the end of October, and we just got our first snow storm of the year. It was 20 degrees out, and I didn’t put the muffler in yet. So I got it cranking and it finally started. Loud, lopey, but started. I noticed that the temp light came on. The folks at Autozone gave me the wrong temp light. So I got one that would turn on at 210 degrees from American Volt, here in Denver.
Later that week, I got the cooling lines for the transmission in, the exhaust, and tranny filled. it was ready to rock and roll. I started it, and put it in gear, hoping for the best, but expecting the worst. To my delight, the car started rolling, and I was off. I took it for a midnight spin. It drove great. Not bad for a $300 tranny, I must say! I drove it for a week. The biggest issue was the temp of the engine. The light kept turning on on the highway. It wouldn’t over heat, but it would get hot. I finally tracked it down to the water pump. Almost 60 years of sitting isn’t kind to a Water pump. The darn thing had more more rust than not. So after replacing it, it cools fine. No lights. Radiator is warm to touch, but not hot. Second issue was a hesitation. Autoline sent me a rusty carburetor. After rebuilding it, it runs fine.
Conclusion:
After 2 weeks and over 1000 miles put on the car, I would call it a success. Under normal driving, the transmission shifts around 2000 RPM. The engine can rev to 4000. Never tried any farther (Nor do I want to.) The highway on ramp is interesting. The car goes 0-60 in 17-18 seconds. You kinda have to put in in first, go to 40, put it in second, rev it to 60 and rest is third. It isn’t fast, but I don’t care. Its still the comfortable luxo-boat that it once was. My question is, was it too much car for such a small engine? Give me your honest to goodness thoughts! I am happy that I put such an engine in. It gets 17 MPG on average! It was a challenge, but loved it.
As to driving it in the mountains? Oh trust me, I giggle. And so do my passengers. Driving on I-70 in the mountains is a blast. 45 in second gear, near flooring it, and cars flying past? And then going 80 in third gear down hill, no throttle, passing other cars? It certainly is interesting. However, I still get 15 MPG in the mountains, so I am happy. On open, flat highway, cruising at 60-75 is no problem. I can get 20 MPG that way. The best I even got out of the 429 in open highway was 14. So yes, an improvement.
Anyway, Yes, I am making lots of memories. Not something everyone my gets to do with an old car.
Update:
Car has been running great. Did a transmission fluid change and band adjustment around 148,500, an oil change at 150,000. That’s 13,000 miles since I did this engine swap!
1971 Mercury Monterey: You Could Have Had A Marquis Jason Shafer
1971 Mercury Monterey: Why Am I Here? Eric703
1973 Mercury Monterey Custom: A Great Name’s Last Ride JP Cavanaugh
1973 Mercury Marquis Brougham: Time Can Change Me, But I Can’t Trace Time Edward Snitkoff
1974 Mercury Meteor Rideau 500: A Real Canadian Survivor VinceC
1976 Mercury Marquis: John And Margie Come Visiting From Cut And Shoot Jason Shafer
I like to to tinker (and have done an engine swap in the past) but all that work for a 6 MPG improvement? Surely there was a modern engine that would have made more sense?
Must be an engineer. Ooo, I’m in trouble now.
Hello? Did you read the article past the headline?
The old engine blew along with the transmission.
The work had to be done regardless.
Either a modern engine or rebuild the 429- or even a 351 with electronic ignition and fuel injection.
Brilliant and quite eccentric story, couldn’t be better fitted to the ethos of this site, “Every car Has A Story”. And thank you for telling it.
Honest to goodness? It’s a pity you couldn’t have waited for a 300 six. It would hardly make a rocket, but 1.7 litres (or 103 ci) extra would, I suspect, give considerable more oomph but about the same economy, and possibly even a bit better.
Oh, who cares? Some great old barge continues in use, and you enjoy it, and surely, that’s all that matters.
AMAZING story! You, sir, are an engineer of the homemade variety. The type of man who can change the way things are done. Love the story. Have fun with your Luxo-barge. You need some clothing to go with it, which I am supplying in the attached photo. The store is three blocks down from you on the left. Give them my name. Again, brilliant engineering and patience!
Is this what they call a “well-oiled machine”? lol
Looks like that one guy PEED himself.
He had the will and found a way! This is a wonderful way to keep an old Mercury alive and kicking. It also sounds like he is putting a bunch of miles on the old girl, too.
A couple weeks ago I stumbled upon a YouTube video of something similar, with a guy putting a Ford 300 in a ’73 Galaxie. Here’s a video…
Just wow. “Because I can” is as good a reason as any. I have to wonder if he might have gotten the same mpg results with a 302 V8.
Next up – convert it to a 5 speed manual?
Great story! It’s not the choice of engine for resurrection, that surprises me. Rather, the choice of car. Peak Malaise Ford.
This is the coolest! This is the kind of content I want to see on those YouTube channels – a methodical, reasonable swap, keeping it mostly all corporate. Well done!
Put the right engine back into that poor thing!
I had the same idea back in high school, I used to walk by a gigantic 1970 Polara that never moved, and trying to figure out how I could afford to drive it I had the idea to put a slant six in it. Nothing ever came of it, of course but I applaud this guy for making the dreams of a 14 year old come true.
Slant six was actually available in some C-body Polaras and Furys, I looked a a slant six ’71 Fury I once. Of course important changes like different axle ratios made it more viable.
I knew the 225 was offered in the C-body Fury, but didn’t know it was offered in the Polara! But I just looked it up in an auto encyclopedia and yep, looks like the Polara offered it for ’70-72. In 1970 I believe it was only the base 4-door sedan, but I guess they could have expanded that for ’71-72? Although hardtops were often considered more of a luxury offering, and probably less likely to have a smaller engine, and I’m sure there was no way they were trying to put the slant six in a C-body wagon by then!
318 was the smallest in a Plym/Dodge wagon, and 440 standard in most of the T&Cs!
It’s a very interesting story, and I’d bet he isn’t alone out of the relatively-cheap gas US.
Just as Paraguay has long been a diesel-engined country for a long time (even S-Mercedes were easy to find with diesel engines), Uruguay had a tradition for downsizing big cars engines, at the cost of no power at all to speak of, but at least being able to move the cars. That was before every other car had a downsized engine capable to sip fuel and move briskly most cars, so the trick lost favour.
All that for 15-17 mpg? Nope. For that gimme my Tahoe Z71 with equal comfort and space but a lot more features (heated seats, CD changer, power adj pedals, moonroof, tow pkg) and a WHOLE lot more acceleration!
Great story. I applauded you for your perspicacity and ingenuity in solving your problem. Not least in executing it once you mentally decided what to do. Engine swaps of this nature where the replacing engine was never intended can require much modification. If you are not an engineer you could be if you chose. Thanks for sharing your story.
I don’t get the negative grumbling. This guy is like The Professor on Gilligan’s Island. He thought it all up and figured it out and built it just the way he wanted it. Nice work!
I completely agree. Three Cheers For Mr. Highlander! Good for him. Here is a guy who knew what he wanted to do and had the knowledge and skills to actually make it happen. I hope he gets to drive the car forever.
PS To those who are so quick to criticize: Please post the details of the engine swaps you have done so we can see how you think it should be done.
Only the one. SBC/TH-400 replacing the 202/Trimatic in my HQ Holden.
3.36 Banjo to 3.08 Salisbury diff.
Did my own engine harness, accelerator and shift linkages. The latter was a challenge since the TH -400 has the shifter shaft on the left of the case, and I wanted to keep my column shift.
A whole day on that linkage.
I think the carping suggesting a small-block would have been a better choice miss the point. Yeah, probably an easier, more practical endeavor, but it wouldn’t have been half as cool for onlookers when he pops the hood of that big ‘ole seventies Mercury land barge to see a six.
It reminds me of that guy who put a 2.3L turbo four in an Edsel, or the one who put a slant-six in an early fifties’ Ford sedan.
Now, I’m kwondering what was the last year Ford offered a six-cylinder powered, full-size car.
I think 1972 was the last year Ford put a 6-cyl in a full-size. 240 6-cyl, something like 103 hp. I always wondered by Ford didn’t make wider use of the 240. Seems like it had a bit more power than the 250, for whatever reason. But, maybe it was a heavier block, more expensive to produce, etc?
The Ford 200 and 250 didn’t adapt well to emissions controls, and seemed a bit low on power, compared to similar displacement engines from GM and Mopar. I wonder if the same would have held true with the 240?
Its an interesting project that, like most, does not have a solid cost/benefit result but allows the builder to explore and create something they want. This one just subtracted performance rather than add it. For that I salute the builder. Unlike most projects he ended up with a functional vehicle at the end.
That 200cid engine does not look as lost in the engine bay as I thought it would.
Interesting but given the same effort why not the big 300 six, or at least the 240? We drive a lot in CO since 2 of our 3 “kids” live there. We’re going out again next week actually, and we even keep our RAV4 out there so as to have a car available without having have to rent for several weeks each time on our 3 or 4 yearly visits. So we do a lot of motoring in the mountains to daughter’s Silverthorne vaca condo and various road trips. I cannot imagine driving such an under-powered car out there… having to floor it all the time for the frequent ascents how much fuel would you save anyway? An axle ratio change would have been desirable. Nice job though.
It’s barely March, but I think this is a top candidate for best post of the year. Thanks Paul, for finding this and sharing it with us, and especially thanks Mr. Highlander for doing this and putting it out on the Internet. Anyone can do an SBC or 5.0 swap; this one required imagination, creativity … and self-confidence.
This is pretty cool for sure! I don’t drive fast anymore either. Right after my 06 Impala SS back in the day, I’ve slowed way down.
I must say this reminds me so much of my way underpowered 82 Caprice with the 229 V6!! Now that was poorly engineered. I’d imagine this has more torque.
Well done
Interesting project. I guess if you really like the car, the amount of effort to complete the job would be worth it all.
Case in point: I’m reminded of a guy in HS who had a ’65 mustang with the same 6-cylinder in this article, coupled with a 3-speed manual. He insisted on replacing the 6 with a 302 v8. What a mistake. The front and rear suspension, wheels, and trans needed to go, as the factory V8 and 6-cylinder had totally different underpinnings and requirements.
It would have been easier just to sell it and find a V8 version, which were plentiful back in the day.
Back in the day (well, 44 years ago) I had the same idea with a 1974 Ford Maverick that originally came with a 250 I-6. At the time, I worked for a Ford dealer whose service manager had a rebuilt 289 V8 at a good price. I thought it would be relatively easy to swap in the 289 in place of the 250. Not really.
As I recall there were some parts from the V8 Mavericks that I could use to help things along, but I had a fair amount of fabricating to do. And let’s not mention trying to jam headers into that incredibly tight engine bay. In the end, I had an even more nose heavy, poor handling car than when I started. On the other hand, it drove much better and actually got better fuel mileage than the six cylinder !
Like your example, it would have been simpler to find a V8 Maverick to make all of the changes I wanted.
Old TBI 350 small block chevy with the 700R4 transmisson did 18 city/25 highway in my 1991 Cadillac Brougham. That car had the trailer tow package with a 5000lb rating as well.
I dont get it. All this work, you could have swapped to a modern, smaller, more fuel efficient v8 with an overdrive transmission. Would have similar power output to the guzzling big cube v8 and get similar mileage to that six cylinder combo.
Some people need to have their fingers broken with their own wrenches.
Absolutely ridiculous. If anything, a 5.O from an old Mustang and an AOD transmission – to give the torque to move this car and get better mileage than this wretched old 6. On top of that ruining the electrics and A/C to do this too. Sacrilege. This is a beautiful car ftom the 70s and deserved more. Just because you can doesn’t mean you should do it – but in these times that’s out the window, even here. For Pete’s sake.
My only concern would be stressing the drivetrain over time to failure especially in the mountains. I dream of one day getting a 1978 Lincoln Continental and swapping in the bigger I6 from Ford or even a 2J from Toyota. Similar or greater power than the original 460 and less weight seems to be a win/win and probably more reliable overall.
This is a throwback special. My parents had one in silver blue with a dark blue top and interior, including the 8-track tape player and the big V8. I have fond memories of it.