hey peeps - finally joining Moparts! Figured I'd chime in with my recent experiences with "RV-440-3" engines to help clarify some things, particularly with the water pump housings and thermostats. Some of this will be repetitive and some not. I think it's pretty close to accurate but welcome any clarifications.

Background. My truck is a 2002 Dakota quad cab; 78 "RV" 440 from a 79 Winnebago Motorcoach, 46RH trans w/SMR adapter, Atlas 4, D60/14B, 40" Toyo's on Hutchinson beadlocks - the truck is built for rock crawling and hard core overlanding - I call it my 'Rocklander'. Lots of strong hardware and modern touches including Holley Sniper EFI and a CVF Racing serpentine kit.

My particular 440 is date coded 1978, and because it was intended for an RV is actually has a few minor but important differences between it and a standard car or truck 440. First, the RV 440s were designated at a 440-3, whereas I think the car/truck 440s were 440-1. The major differences were mostly related to cooling, meaning as mentioned above two additional cooling ports at the outer edges of the cylinder walls, with (or in my case without) heads with the matching additional cooling ports, and, the big distinctive difference, the RV heads had 5/8-socket spark plugs with a non-crush-washer seal. The heads that were on my 440 are the typical 452s with the normal 13/16-socket plugs and crush washers, so either my 440 just didn't get 'em...or more likely the owner of the RV had the heads swapped out for non-RV heads - my engine did have Fel-Pro head gaskets on it, which was not original, so a head swap was most likely. Also, and here's the kicker specifically regarding cooling - the RV 440s also received a specific water pump housing, pn# 3751216, easily distinguished by either the CB on the front inlet or the additional bypass port under the thermostat, AND...a specific/matching thermostat, which I discovered is kinda important.

RV water pump housing (note the two cast recesses for the thermostat and bypass port) -



Also, I discovered that a "skirted" thermostat must be used in conjunction with the RV water pump housing - at least it does if you want it to be cooled properly. The 440-3 thermostat has a lower 'skirt' which when opened lowers down into the recess below it which blocks off the bypass port in the water pump housing, sending the majority of the coolant through the radiator...and without which (with a typical non-skirted thermostat) will not block the bypass port, which will not send the majority of the coolant to the radiator - it will just continually 'bypass/circulate' most of the coolant within the block/heads (the intent being to warm up the engine rapidly) and some will go through the radiator, but not all, which I believe is why my 440 wasn't cooling well (it was cooling so-so, but not great) - and yep I had a standard 440-1 thermostat in there. My intel indicates the Mr. Gasket 'stats are of marginal quality but the Milodon ones are good. Pics of the Milodon (silver top) and Mr.G skirted thermostats -





...compared to a non-skirted 'regular/non-RV' thermostat -



But wait - there's more. The RV water pump housing has a recess just below the top which fits the thermostat perfectly, but the non-RV pump housings do not. And, all of the upper thermostat housings I've found have a recess in them too, which according to the books is to center the thermostat in the 440-1/non-RV applications. Now, because the thermostat lower skirt is supposed to extend down into the lower recess and block the bypass coolant flow I chose to presume the thermostat...in the RV applications...is supposed to be placed in the pump housing itself, and not in the upper thermostat housing. I don't think the thermostat is supposed to go in the upper housing, because if it did then there would be the chance of it not aligning with the lower recess, so I went with the lower/below-the-gasket placement. Then, UltraGrey RTV, gasket, more RTV, and upper "thermostat" housing went on, bolted to 18 lb/ft. I'm pretty sure my cast iron upper thermostat housing is not for an RV application and is simply for all the 440-1 applications. I have not yet found a genuine "440-3 thermostat housing", but if I did I'd wager there is no recess in it for the thermostat.

But still, my thermostat housing had that recess in it...or at least it used to. To try to get maximum clamping and sealing potential from it I went ahead and had a local welding shop do the proper cast iron welding to fill in the recess, and I machined it flat - actually I machined it to perfectly match the pump housing with just the slightest detectable amount of center 'rise' to get that much more clamping on the gasket.

Here is my upper thermostat housing 'filled in' -



...and sanded flat -



...and Permatex 27036 'max torque' ultra grey to seal it all up -



Results: In the 2 hours or so of having my engine alive it had the standard non-skirted thermostat in it, and its been running between 210-225 the whole time. But after installing the skirted 'stat it got to 180* and tossed the anchor - never going a degree higher .

Anyway, hope this helps anyone else out there who has the RV hardware, especially in the cooling department.

Cheers,
- Sam