Urgent--need explanations: dodge 440 cooling system

[obleck]

Hello all!  Newbie here.  I'm urgently trying to get my "vintage" 1978 Dodge motorhome running, and it's got overheating issues.  It's running a Mopar 440 on all 8 cylinders and goes down the road fine, but it's getting too hot.  230 on undulating hills at say 60mph+/-, and 260+ on long steep uphill.

The radiator isn't original, but it's about the right size.  It also has two electric fans built in with a switch to turn them on (system is an add-on it seems).

The fan clutch seems fine--a buddy suggested trying to stop it from turning with a newspaper, and it just shreds away.

It's supposed to have a jacketed thermostat, but it's just got a normal one--availability issue.  The reason for the jacketed one is to limit the coolant flow to the radiator apparently.  However, I can't imagine that would make a 30-50 degree difference.

I flushed everything, and the radiator seems to be in good shape.

I don't know if there's a head gasket leak into the cooling, but I'm not getting any froth, maybe an occasional bubble I've seen, so if it is leaking, it's not much.

However...  I can't for the life of me figure out what's pumping water through the radiator.  It seems like it's passive!

I've attached an ugly sketch of what seems to be the coolant circuit.  You'll notice that both the top and bottom radiator hoses go to the low pressure side of the water pump housing (i.e. the back). 

Here's links to the water pump housing as well on 440source:

http://www.440source.com/1001074.jpg
http://www.440source.com/1001075.jpg

(3rd one down on this page:  http://www.440source.com/wpumphousings.htm)

Any thoughts?  Or am I missing something with regard to the water pump housing?

Thanks!

 

[Rene T]

The 3rd picture down shows a place for the thermostat right on the pump yet your diagram shows the thermostat near the radiator. Am I missing something? Do you have two thermostats?

 

[obleck]

Oh, sorry, just a schematic. The thermostat is mounted on the top port of the pump housing as usual and has the upper radiator hose coming off it.

 

[ijsa]

Have  you  tried the thermostat in a pot of boiling water to see if  it  is  opening  and  closing  properly?

 

[obleck]

New thermostat, same result as the old one.

As a side note, the radiator does get hot, so the thermostat does open or the water would be pretty much cold.

What's baffling me is that there doesn't seem to be any water being *pumped* through the radiator when the thermostat is open.  It's just passive.  Ordinarily you'd expect to see some movement when say the radiator cap is open.

 

[Rene T]

New thermostat, same result as the old one.

As a side note, the radiator does get hot, so the thermostat does open or the water would be pretty much cold.

Just the opposite. If the thermostat did not open, then the water would get real hot fast. Maybe it's not opening.
Maybe the entire system needs a good chemical flush.  You said you flushed it. Did you use just water or did you use a chemical like this:

https://shop.advanceautoparts.com/p/bluedevil-radiator-flush-00204/10449728-p?c3ch=PLA&c3nid=10449728-P&adtype=pla&product_channel=local&store_code=6753&gclid=EAIaIQobChMItdO4v9SP5AIVBeXICh3OlAX4EAQYASABEgJUYfD_BwE&gclsrc=aw.ds

 

[obleck]

If the thermostat is closed and thus no water is circulating through the radiator, why would it have have very hot water in it?  Maybe slightly warm from some heat conduction on the lower hose.  The upper hose is plenty hot too.  So I'm pretty convinced the thermostat is working.

Flushed with some Prestone flushing product.

Anyway, all that aside, my question is how is water pumped through the radiator?  It would appear I can take the thermostat out and still there is no active pumping of coolant through the radiator since no hoses are connected to the high pressure side, thermostat or not.

 

[SpencerPJ]

Are your upper and lower hoses old?  They could be collapsing under heat, higher rpm,  and pressure.  Is the belt around water pump in good order?  It could be slipping at higher rpm.  I've really never heard of a pump going bad, seals leak, but impeller ??  I suppose it happens.  And I know Rene is a smart guy, and I'm incorrect at times, but I too thought if the thermostat is stuck, it wouldn't allow the coolant to circulate, and the radiator would stay cooler, bottom hose hot, top hose cold. 

Edit: Water pump spins, circulates water if the thermostat opens.

 

[darsben]

I do not understand the high pressure side. The pictures you provided specially attached image number three  show two different housings for the  water pump. One is high output the other is not. The mounting seems exactly the same, could someone have replaced high output with a regular duty housing?

 

[Rene T]

I'm just saying that if the thermostat is stuck shut or not fully opening, the temperature would rise in the engine block and the temperature gage or idiots lights would indicate that.

 

[NewmanRacing]

If t-stat is stuck closed, top hose and radiator cool, bottom hose warm, engine gets quite hot fast!

I drove stock cars for many years. Keeping the engines cool was a task.

Your water pump will circulate the anti freeze. Check the radiator between the radiator and AC condenser for debris accumulation.

 

[obleck]

Hi Everyone, thanks for all the responses!  This is still baffling me.

A few responses to questions:

Correct picture is this one:
http://www.440source.com/1001075.jpg
]It has a very large opening to the t-stat, as opposed to some of the others.

Fan belt good, hoses good as far as I know (I'll take a look at the bottom hose for collapsing again next time I do a test).

Water pump fine, no leaks, blades are fine.

Darsben, you might be onto something.  So looking at this one, http://www.440source.com/1001075.jpg,  is that a high output or not?  The thermostat opening is ported to the rear of the housing, which is the intake side (i.e. low pressure) of the pump impeller.  What is baffling is that the lower hose/port is also connected to the back side as far as I can tell, and thus the high pressure side (i.e. the front of the housing) only feeds to the block (left and right), and the heater, but NEVER the radiator.  Yes? No?  Baffled, but not wanting to pull it out.  Like I said, if I shove a garden hose into the top/thermostat port, it seems to just comes out the bottom hose immediately.

Put another way, this thing seems to always be bypassing the radiator, except when the t-stat opens, the radiator is passively connected.  Makes no sense.

 

[darsben]

the image I am looking at has the caption
"Shown above is a 3751216 housing, Chrysler # 3751217. Originally used on motorhome 440's from 73-79. Nearly identical to the above car housing, as you can see by comparing the pictures, however the opening under the thermostat area is slightly different and much larger for increased water flow."

The image attached in your post immediately above is marked the same as the high output one seen in the original post image which i referenced above

 

[TheBar]

Are you sure the gauge is right? The springs in old gauges get weak and register too high. Shoot a laser thermometer at the engine block and radiator and see what the readings are.

 

[Lou Schneider]

The radiator isn't original, but it's about the right size.  It also has two electric fans built in with a switch to turn them on (system is an add-on it seems).

How deep is the radiator core?  It may be the right size dimensionally, but if it's not deep enough it won't have enough radiating surface to dissipate the engine heat under load.

Do you have the plastic radiator shroud so the main fan can suck air through the entire radiator?  If not this can also reduce the radiator's efficiency at dissipating engine heat.

 

[grashley]

As I understand, a CLOSED thermostat forces the water pump to recirculates coolant thru the motor.  No flow to the radiator, no heat to radiator.  An OPEN  (or no) thermostat and the water pump forces water to the radiator, thru the upper (hot) hose.  The lower (cooler) hose returns coolant to the motor.  The water pump low pressure inlet is the engine block.

Water pumps DO go bad.  Sometimes they leak.  Sometime there is no leak, but the propeller in the pump comes loose, and no water is pumped.  I have replaced bad pumps from each group.  Modern cars and trucks rarely have this issue, but we are discussing a late 70's engine.

Other issues may be a replacement radiator that is SMALLER than the original.  The dirty radiator may also be a factor.  Run with no thermostat and see what you get.  Thermostats are there to help the motor warm faster and prevent over cooling!  Checking temps with a IR gun is a good suggestion, too.

 

[cerd]

I would replace the thermostat with OEM equivalent. Some brands have a high flow thermostat for things like tow trucks and RVs that tend to operate in hotter environments, with more abuse. I would go that route. You can either use a 195 degree t-stat or a 180, but I wouldn't go as low as 160. That may prevent your engine from running at optimum temp.

There is a chance that your pump is bad. I have seen some that didn't leak, but had a damaged impeller, preventing proper flow.

You can always get some fittings from your local hardware store and make an adapter to connect your garden hose to the radiator hose to make sure the radiator is flowing correctly. The pipes in a radiator are usually pretty small with the fins descipating most of the heat. Almost all of the coolant is stored in the tanks on the top and bottom or sides.

Honestly, with an older rig like that, I would just replace the water pump, fan, T-stat, and hoses just to make sure that they are all in good working order. If you order from Rockauto, you're looking at about $80 worth of parts. Just change them and be done with it.

Clutch: $25
Pump: $20
T-stat:$3
Hoses: $15

There's probably a shipping fee, but its usually about $10-15.

 

[obleck]

Hi All,

Thanks again for the responses.  I'm going with what I got...

A buddy of mine had a slightly smaller but 4 level deep new-ish AL radiator, so we threw that on.

Also did Prestone coolant flush thing as previously noted.

Took out thermostat altogether, despite potential downside.

Coolant does flow in radiator but not as much as I'd like to see.  Still baffled by how this thing appears to be plumbed.  I'd have to take it all apart to see what is actually going on.  It is the high-flow version of the housing by the way.

Again, pump okay, hoses okay, gauge okay, etc. 

Anyway, some improvement but not 100% yet.

It stays around 210s, maybe up to 220 on the highway with some rolling hills.  I also took it up a steep 2-3 mile hill here (my "test hill") at 45 and it hit 235-240.  Just have to nurse it a little on those I suppose.

It's possible advancing the timing a little would help.  i.e. make it more efficient = less waste heat for same power.

 

[72cougarxr7]

If the radiator was replaced, it may have to small of core thickness.
A heavy duty application like an rv, tow truck, etc, traditionally has a 3 or 4 row radiator. If someone replaced it with a standard truck rad that was only  2 row, it might not have enough capacity.
Also, on the thermostat, I have had good luck with stant "superstat" thermostats. They are stants premium line and have a larger opening to flow better than the standard units. Also have bigger heat motors for more consistent opening, and are made of stainless steel.

A belt driven water pump rarely has impeller failure, if they fail it is typically in the bearings or seals and they l eak or get noisy. While not impossible, impeller failure is  very rare.

 

[TheBar]

The OP keeps repeating very little water flow. Even without the thermostat. That leaves the water pump, radiator, hose collapse, or a corrosion blockage in the engine block or radiator. I agree with Cerd. $80 in parts is cheaper than a mechanic. Who would replace all those anyway for twice the price.