1979 F100 Cooling System
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Cooling System

As part of the EFI conversion and AC additions, the cooling system needed some work. The original radiator was the oddball narrow/small one, and had been replaced with the more normal wider one shortly before I got the truck. The shroud was on it's last legs and split in two, but there and sort of functional. The heater hose hookups had to be modified to work with the AC setup and combine the Mustang bits as well. I also needed/wanted to hook up the heated throttle body setup on the Mustang engine.

The Mustang heater hose pipes that run along the intake manifold will not be used for my EFI conversion on this truck. The AC (or Deluxe Hi-Lo Heater) setup has the heater hose connections along the fender edge and they are about 2/3 of the way forward along the motor, so running the pipes to the back of the motor as they did on the Mustang makes no sense here. I'll be running the heater hoses directly from the intake/water pump to the heater, the same as they were run originally. That left an open question on what to do with the EFI temp sensor, though, because on the Mustang it installs into the heater hard lines along the intake manifold. To solve this, I opted to use the heater hose outlet on the intake manifold from a 1987-1989 F150 with a 5.0L - earlier or later years may work, but I know those years work for this. It has provisions for the temp sensor, has an extension tube for the heater hose outlet to move it over to the edge of the engine, and has a smaller outlet fitting for the heated throttle body (should I choose to go that route). I snagged this one from the original engine in the 1989 F150 I worked on, and that's why I knew about these fittings. I did have to massage the Mustang EFI hard lines that run down the front passengers corner of the motor to make it all fit, but it was mostly pretty minor hand adjustments to the hard lines.

For the heater core hose hookup at the water pump, I ended up using a Gates 18774. It's a 5/8 diameter hose with an S-bend in in it, and one short leg and one longer leg. I trimmed about an inch off the short leg and used that end to connect to the water pump. The long leg then goes up and over the alternator and has a straight union to connect to the regular heater hose going to the heater core. I also looked at a Gates 28467 which has a simple 90 degree bend in it and one short and one long leg. The old engine had a Gates 18800 on it which is roughly P-shaped, but without the back section on the P. This worked well with the old setup to run the heater hose under the alternator, but on the new engine the heater hose would not fit between the alternator and the smog pump (no space between the bracket for the hose), so I ran it up and over the top of the alternator. It's more noticeable, but it'll work.

The upper and lower radiator hoses are stock 1979 F100 pieces for a truck with a 302 and AC. I replaced the top radiator hose, so I know it's a Gates 20860. The bottom radiator hose was in OK shape and was simply reused, so I don't know what the exact "confirmed to fit" part number is. It should be easily available in any parts store, though, and you don't have to remember any special applications.

I looked into keeping or bypassing the heated throttle body system, and I've decided to keep it. These are the small coolant lines that go from the heater hose hookup near the front of the intake, into the EGR spacer, and then back to the rear of the intake manifold. This passes coolant through the EGR spacer and does two things - 1) it warms the EGR spacer and throttle body assembly quickly during cold weather operation, and 2) once up to temperature it acts as a cooler to keep excessive heat from the EGR from causing problems. If I wanted to bypass this, I could simply plug up the passages at each end - the rear coolant port on the intake manifold uses a typical NPT plug and you can put a similar plug in the F150 coolant outlet on the front of the intake as well. I don't know the size offhand, but you get the idea. I'm keeping the system functional, including the EGR and all the other pieces to stay as close to the factory setup as possible - I don't care about ultimate performance in this truck, I just want it all to work as the factory intended without odd problems. And since the heated EGR spacer/throttle body helps with cold weather drivability, I'd like to keep it. The EGR keeps emissions down for relatively no cost in power because it's not in use at WOT, which is nice. I intend to use this truck as a truck and hop in and drive it, even if it's cold and raining out when throttle body icing could be an issue. I did some research on carb icing, and it can happen well above freezing, especially if it's humid out. EFI systems are not as prone to the problem, but it does happen in various cases. Since my area (Seattle) is prone to very damp and fairly cold-but-still-above-freezing winter weather for weeks at a stretch, I'm keeping the heated throttle body system functional. Since the Mustang setup uses 1/4" coolant lines and the F150 outlet uses 3/8" coolant lines, I will need to change out the hose fitting on the F150 coolant output on the front of the intake to be one with a 1/4" hose barbed end on it - a small brass fitting from the local parts house should do nicely. I found that a 90 degree fitting worked quite well and could be installed without removing the temp sensor or the heater hose. Add in two short lengths of 1/4" heater hose to hook everything up, and it's done. The 1/4" heater hose is available from various parts stores, but you may have to order it in. Don't use fuel or vacuum hose as coolant hose - get the right stuff so it lasts a while. Also, be aware that many catalogs specify 3/8" hose for the small coolant hose hookups fittings on the Mustang EGR plate and on the back of the intake manifold, but that the fittings are way smaller than what you should use with 3/8" hose. I found this out the hard way. It is possible to tighten the hose clamps enough to make the 3/8" hose work, but it's far better to just get the right size hose in the first place.



I managed to track down an intact fan shroud from a 1978 F150 with a 351M, and it looked like it would work just fine. Later on I found out otherwise, but it was a cheap experiment. You guessed it - it was yet another Craigslist-sourced part.

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Here's the heater hose outlet on the intake manifold that came from a 1989 F150. The temp sensor, heater hose, and hookup point for the heated throttle body line are all installed. You can also see the Mustang EFI hard lines that come off the fuel rails and head down the front passenger's side of the motor. They are close to the heater hose, but there should be enough of an air gap to prevent boiling the fuel on hot days.

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Here's the radiator and fan shroud reinstalled. Too bad the fan shroud didn't work out - see notes in the Fan Shroud section for more details.

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Here's the heater return hose to the water pump installed. You can clearly see how the molded hose was routed, and the union the connects the molded hose to the regular heater hose. I left enough slack in the hoses so that the air intake and MAF sensor could go over them later. I may need to reroute things later on, but for now this is plausibly right and workable, at least well enough for more installation work to progress.

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Here's the fan temporarily installed, minus the 351M fan shroud that turned out not to work.

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Here's the upper radiator hose installed. I ended up using a Gates 20860 which is the listing for a 1979 F100 with a 302 and AC. It looks nothing like the original hose I had from before, but it works and clears the belt tensioner pretty well. It did need to be bent slightly out of it's natural shape to fit, but not much. It also touches the tensioner and the heater hoses in a couple of places, but it ought to do OK. Time will tell if rubbing-induced hose wear becomes a problem. If so, you can put various protectors over the hoses to help with that. Even a split open piece of old radiator hose wrapped around the new hose will work in some cases.

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Here's the heated throttle body hookups. When I filled the engine with coolant, I forgot about the rear coolant port on the intake manifold and since it was the lower than the front coolant port on the manifold, it started dripping first. It was a good reminder that it was there... :-) The second photo is the same as the first, but with the different ports for the heated throttle body hookups highlighted. The two manifold ports are circled in red, the two throttle body ports are circled in blue. When I took the picture, I had a long piece of fuel line on the rear port on the intake manifold in a vain attempt to keep it from dribbling. Also, in the photo above of the upper radiator hose, you can clearly see the F150 heater hose outlet on the intake manifold with the open port for the heated throttle body hose, plus the forward port on the EGR spacer where that hose would go to.

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Fan Shroud

Here's the original busted 302 fan shroud from the truck. The first picture shows it like it was installed on the original radiator, the second shows how it was spread (at the helpfully busted areas) so it would fit the wider replacement radiator that was previously installed. Compare the bottom of the fan shroud to the pictures of the 351M shroud below - note how the fan opening/circle protrudes below the bottom line of the shroud on this one, but not on the 351M shroud.

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Here's the shroud I found from a 351M equipped truck. It was the right width, but note how the bottom of the fan opening/circle stays at or above the bottom line of the shroud. Compare to the original 302 shroud above to see the differences.

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Judging by the measurements I took off the radiator and fan shrouds, the original "narrow" radiator in this truck was something of an oddity. Most truck came with the wider radiator, and thus the wider fan shroud. I guess I need to hunt around on Craigslist some more with some dimensions in hand...


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Page last updated 06/28/2009 01:44:19 PM