Magnum Serpentine on a '91 TBI 318? Without changing the intake?

-
DionR

DionR

Well-Known Member
Joined
May 7, 2008
Messages
4,887
Reaction score
2,396
Location
Spokane, WA
I've got a '91 Dakota with the 318 TBI and the serpentine belt tensioner visually looks to be on it's last legs. I've had the tensioner go bad once already and the truck was down until I found a used one in a JY. They are a one year only part and are no one makes a replacement. The likely hood of finding another one that is good seems slim.

The ultimate fix is the 5.9 SMPI swap I am working on. I have most everything but am still assembling things and am not quite ready to do the swap. I also need the truck for winter driving and am concerned that the swap could run into a snag and sideline the truck for an extended period of time when I really need it. I've been planning to do this swap during the summer, but missed that window for this year.

The temporary solution that crossed my mind was to swap a full Magnum serpentine front end onto the 318. I have all the parts, including the non-AC bracket. This would also allow me to replace the cracked radiator with the new '92 one I bought for the swap.

The only issue I can think of is that the TBI thermostat housing could potentially cause an issue. It points at the wrong side of the radiator and might crash with the Magnum alternator.

Just curious if anyone has done anything similar. I figure I will do some more inspecting and see what I see but thought I would just toss it out there to see if anyone has any experience.

Thoughts?

Thanks.
 
Wouldn't you just need to switch the thermostat housing to a regular vertical hose attachment to fix this conflict?

Sounds like you are planning a non-AC swap. Is that correct? I am looking for pictures I posted once of a 91 Dakota I found in the junk yard for reference but have not found them yet.

I forget if the angled 91 Dakota thermostat housing is large or small style, but both are available in typical vertical layout.
 
Bobzilla said:
Wouldn't you just need to switch the thermostat housing to a regular vertical hose attachment to fix this conflict?

Sounds like you are planning a non-AC swap. Is that correct? I am looking for pictures I posted once of a 91 Dakota I found in the junk yard for reference but have not found them yet.

I forget if the angled 91 Dakota thermostat housing is large or small style, but both are available in typical vertical layout.
Click to expand...

I guess I was thinking that I couldn't change it. The thermostat gasket is leaking anyway and I had planned to fix that at the same time. I will look into it more.

Correct, the truck is a non-AC truck so I don't have to worry about a compressor complicating things.

I did take a peek last night and best guess is that even with the angle thermostat housing it would work, but the hose would be kind of weird. Changing it would mean I could run the '92+ upper hose at the same time, even more parts I wouldn't have to replace when I get the 5.9 Magnum swapped in.

Thanks!
 
Have not found my pictures yet. Can you post a picture of your intake showing the thermostat housing location?
 
Bobzilla said:
Have not found my pictures yet. Can you post a picture of your intake showing the thermostat housing location?
Click to expand...

Probably going to be a little while before I can. But will get something.
 
No hurry for me. I actually have a 89 model year 360 LA TBI engine sitting here right now and all the Magnum serpentine parts. I was thinking I may be able to mock it up for you but would need to know if your thermostat housing location is the same as mine. The only thing in your swap that I can think of that would not be perfect would be the bypass hose, but that does work it just ends up a little crooked.
 
Bobzilla said:
No hurry for me. I actually have a 89 model year 360 LA TBI engine sitting here right now and all the Magnum serpentine parts. I was thinking I may be able to mock it up for you but would need to know if your thermostat housing location is the same as mine. The only thing in your swap that I can think of that would not be perfect would be the bypass hose, but that does work it just ends up a little crooked.
Click to expand...

I meant to look into the bypass hose and then forgot. The 318 in a '91 Dakota seems to almost be a hybrid of the Magnum and LA stuff, so I was hoping maybe it would be the same as the Magnum.

But I have a Magnum intake on my LA 360 and had to mess with it there, so I figured worse case I would have to do something similar.
 
Got some pictures.

20221109_121138.jpg


20221109_121150.jpg


20221109_121144.jpg
 
Thermostats and gaskets appear to be a match between the '91 318 and the '92 Magnum. Don't think the existing brace will work so (in theory) the thermostat can be swapped and the '92 hose used with the '92 radiator I will swap in.

Bypass hose doesn't look to be an issue.

Water pump gasket is the same, so should be able to use my existing water pump so the fan shouldn't have to be changed. Pretty sure the pump is different and would require the screw on fan rather than the "traditional" 4 bolt fan.

Alternator is different between the 2 years. Hopefully either the mount accepts the 91 alternator or the 92 alternator works with the existing connections. And probably going to have to fabricate some kind of a brace for the Magnum alternator bracket.

Sticks in my head that the PS pump bolts to the TC cover. I know the Magnum TC cover doesn't have a PS mount, but I think the GC used a bracket that bolts to the front of the DS head that would duplicate that mount.

Going to have to look at the '91 and '92 TC covers. Maybe I can just swap the alternator brackets and leave the TC cover and water pump alone.
 
I think I can swing this except for one thing. The LA heads on the 318 are missing 2 of the accessory bolt holes on the end of the head that the Magnum has.

Luckily the PS pump bolts to the '91 TC cover and (I think) the cover won't need to be swapped. Dodged that bullet.

But the tensioner will be missing 1 or 2 of the 3 mounting bolts. Not really sure what to do there yet.
 
Is that a 6 rib belt? I think the Magnum is 7 ribs. If so, your crankshaft and power steering pulleys would likely need to change as well.

The 91 Dakota is already an oddball, but look at the alternator bracket on that one without AC. Wow. Never seen that one before.
 
Bobzilla said:
Is that a 6 rib belt? I think the Magnum is 7 ribs. If so, your crankshaft and power steering pulleys would likely need to change as well.

The 91 Dakota is already an oddball, but look at the alternator bracket on that one without AC. Wow. Never seen that one before.
Click to expand...

Never even thought about the belt being different. Will look into it.

Hope is kind of dwindling that this would work.
 
Yep, '91 belt is a 6 rib, '92 is a 7 rib.

Might not be the end of the world, in theory I could run a 6 rib belt (if I can find a proper length one). The big hang up I have is how to mount the tensioner.
 
I was looking at my LA engine today, wondering if it may be possible to modify a steel Magnum tensioner bracket to mount to the LA head. The lack of mounting holes like you mentioned would make that tricky.

What is wrong your tensioner? Is it no longer springy, getting stuck? Making me wonder if we can take these apart. I never tried before.
 
I was looking for pictures of the tensioner and came accross this video. Check it out. Guy used a tensioner from a Taurus and swapped on the old smooth pulley and it worked. Maybe this will get you by cheap and easy.

 
Impressive sleuthing! Thanks!

Video is only a couple of months old, makes me feel better that I didn’t find it on my own.

Mine isn’t as bad as his was, but it is starting to sit at an angle like that. I’ve got a pretty good squeak going on, too. I assumed it was the air pump, but he mentioned that so maybe it is the tensioner.

Looks like he is running an alternator for a Magnum, too. Belt looks to be one rib smaller than the pulley.

Really appreciate it!
 
You must log in or register to reply here.
-

Back
Top