Might have a heater core job coming up on my '94 pickup because I've recently flushed it and it's intermittently smelled a little like coolant inside for the past decade of ownership.

I don't like the idea of the 2-piece heater cores that the pickups have, where there's a separate pipe joined to the core under the dash with an o-ring and a clip that holds the flanges together.

Strangely, Toyota seemed to do the preferred 1-piece design on about half of their models, generally being lower-end ones (Corolla, Tercel, Celica) whereas the more flagship models (Camry, Cressida, Supra, Land Cruiser) all got 2 or 3 piece heater cores.

Also strange is that the '90-'95 4Runner got a 1-piece heater core, unlike the '89-'95 pickup that of course uses the same dash.

Comparing pics of the heater core boxes on ebay shows they are different, with the 4Runner holding the core parallel to the firewall and the pickup holding it at an angle, but the mounting areas and duct connections appear like they might be compatible. Any idea if one could easily swap a 4Runner heater core box (ie, the whole assembly) into an '89-'95 pickup?

Pics for comparison:

 

Bump.

 

Welp, here we are about 4 months after making this thread and my '94 pickup's heater core just started leaking on my passenger floor board last night.

Really a best-case-scenario for me, cause my fiance caught it right as we were leaving the house for dinner, so it was no problem to turn around immediately to swap to my '87 4Runner. Plus, I've got some of those Husky hard plastic floormats, which contained the coolant like a tray so it didn't soak the carpet.

A month or 2 ago, I tried flushing my heater core with hose water, and shortly thereafter I tried adding some CLR cleaner in there to let it sit for 2 rounds of 30 minutes each. Saw some small, dark flakes come out, but nothing wild. Seemed to flow ok. Probably made the leak happen sooner.

Was hoping to make the heater a bit hotter since it's always been just kinda warm, especially compared to my '87 4Runner's heat, which is by far the hottest of any vehicle I've ever been in, and it's delightful. Both 22RE.

Never heard back from this thread regarding swapping to the 4Runner heater box, so still don't know if they'd fit.

Plan is to just replace the core with an FVP brand from RockAuto (already ordered; was the last one remaining at this time). It's just a regular pickup-specific core. Also ordered an OEM o-ring on eBay for $10 shipped. Just disconnected the firewall hoses to start the removal process.

If I run into some big issue with this pickup's heater box and/or the replacement core, I think I'm gonna take a swing at trying the 4Runner heater box by purchasing one on eBay since there tends to be 2 or 3 for sale at any given moment. But for now, just for simplicity, I'm gonna stick with the normal pickup heater box arrangement. Fingers crossed that the pipe to the heater core is in ok shape.

 

Sorry I don’t have the answer but my heater in my 91 is atomic!!!! Maybe it is clogged and a new one will do the trick, but I can tell you it should be atomic, have you made sure the linkages are going full on to heat? I have never had to mess with the heat valve unit(not sure what it’s called) on the firewall? Idk just throwing stuff out there let us know what happens!!

 

Yeah, all the HVAC control cables have been in good order, and the coolant heater valve on the firewall has been working a-ok.

I actually just replaced the original valve when I did that 2nd flush job over a month ago. -- Reason being, when I did the first flush like a week or 2 prior, I noticed the tip of one of the 2 plastic nipples on the valve had broken off. There was still enough nipple left for me to slip the hose on, but that let me know the plastic had unsurprisingly become brittle, so I ordered a non-OEM replacement valve online and kept driving with the original one for a few weeks till it arrived to then swap it on. The end of the other nipple broke off when I was removing the valve. Coolant flow through both the old and new valves looked to be excellent.

Unsurprisingly, replacing those valves is a piece of cake. If you've still possibly got the original early 90s plastic heater valve on your pickup, I'd definitely consider replacing it preemptively. The exterior of mine looked like it was still in great shape, but it's the non-visible surfaces that undergo the harshness of hot coolant.

Not sure if anybody's had one of these valves fail in a way where they let the coolant out, but I could totally seeing that being possible, like one of the nipples breaking completely off and letting coolant spew out everywhere. Also, I became worried when that first nipple end broke off that it might be clogging stuff up somewhere in the system.

 

I still have original heater cores in my 86 and 88 pickup. The only leaks were from the O-rings. I measured them and looked up the best material options on McMaster-Carr and ordered a bag of them.

Lack of heat can be either lack of coolant flow through them or lack of air across them. In my case it was always from the Evaporator being turned into a dirt brick over the years choking off any air through the system. Whenever I have the entire box out for rebuild/reseal I run phosphoric acid in the heater core. That was enough to get mine clean anyway. Old school radiator shops can rod out heater cores just like they do with a radiator but hard to find those shops these days. I'm sure many of you already know this, just throwing it out there.

I have seen some forum posts where guys soldered the tubes to the heater core. IDK.....I guess it works but it's not that hard to get a couple O-rings for another 20-30 years of use. Personal preference I guess. These are the O-rings I used. https://www.mcmaster.com/1295N241/#:...n,16%20mm%20ID

I'd like to hear if the other heater box will fit as well.