I've tried three new thermostats all the way down to a 160F model.  The thermostats don't change anything.  She warms up and just goes to the end of the temp gauge and stays there just hover over the edge of the what I assume to be the "normal" range indicated by the white stripe between C and H.  but if I get on her she will close in on the end of the temp gauge range.  She hasn't bubbled over yet but...I've been pretty careful.

When I used my infrared thermometer on the radiator return hose after the engine is warmed up and running Im' getting temps in the 195-200 range, over 230 on the thermostat housing and this was with a 160 thermostat!

I feel like there are only two possibilities.

1) radiator is clogged and not flowing

2) water pump isn't pumping.  (is this possible?  The belt is going around.)

Can anyone think of any other possibilities?

My next step is going to be to stick my garden hose in the radiator, unook the upper radiaotr hose and point it into a bucket and wait for the engine to warm up and then see how much flow comes out once the stat opens up.  How fast should it flow if the pump is pumping properly?

If the pump seems to be flowing well, then I will disconnect the radiator lower hose and power water into the filler opening and see how fast it flows through the radiator and out the bottom outlet.  What should this look like? How fast should it go through? 

Are these good ideas?  Are there different better tests? Anything I'm not thinking of?

Try draining the radiator out the lower drain port - and when she stops flowing - close the valve and refill the radiator with (cheap) white vinegar. Run the engine and let the mild acid clean up a bit of the old lime that may be in there - then drain it out and refill with water.  

What poppet size have the thermostats been? Its common for them to be only about an inch in diameter - and there are some bigger more free flowing parts available. 

The one on the left flows about a third less than the one on the right. For obvious reasons.

The above large poppet thermostat is a "Robertshaw" type that has huge flow capability - and it has been modified with three 3/16 bypass holes. When modified as shown - the short bypass hose at the front of the engine (below the upper rad hose) can be partially blocked with a brass 3/8 pipe plug -also drilled with a 1/8 to 3/16 hole - so that more water goes to the radiator rather than short circuiting back to the pump.

The thermostat being installed backwards is also a possibility.  Is the bypass hose hooked up?  A secondary function of the bypass hose is to remove air from the waterpump and upper end of the timing cover which creates an air lock if that air stays in place.

To it seems more like nothing is flowing at all.  On my other cars I can watch the temp gauge to see when the stat first opens up and the cold charge of water from the radiator enters the engine, you can actually see the needle drops a little.  That is definitly not happening the customline. 

Right now when I start her up and let her sit and idle in the driveway, the needle just slowly climbs to the top and stays there, even if it is just idling in the driveway, it idles way at the top of the gauge range almost to the end.  It never comes down.  Then, if I drive it starts moving even more towards hot so it is almost touching the "H". 

Maybe I will try the vinegar thing too.

T add to what Steve said. After my rebuild including a new radiator (high efficiency 3 row) and electric fan I installed a 160 degree thermostat like the one on the left. O cool days or higher speeds the engine temp was 160, too low really. When it got really warm or I was at low speeds the temp would slowly creep up to 195 (maybe higher I never let it go that high). I switched to the thermostat on the right in 180 degree a drilled one 1/8 inch hole in it. The engine now runs 180 at all speeds and outside temps. And because it runs hotter it runs better, idle is noticeably improved. Mike

1) Water pump is pumping water (pumped water out even when hose was off)

2) Thermostat is working

3) Water does flow through the radiator.

3) As long as I had the hose on at a high enough flow rate (providing as much water as the car could use, so extra water was actually overflowing at the radiator filler cap), the car maintained great temp, it actually got cold enough to close the t-stat.  The temp gun reading below is a reading of the water stream coming out of the engine into the bucket. (the t-stat closed shortly after taking the picture)

4) If I slowed the hose flow rate down.  The water coming out of the engine still flowed well, but temp of the water flowing out of the engine went up to 179-180F?

I don't know what conclusions to draw.  Assuming the water pump is pumping at the correct rate, I guess the only component left in the system that isn't proven by this experiment is the radiator itself.  My hose was providing 55F water (well water) and the engine was able maintained temp with this.  But obviously when I'm driving my radiator isn't cooling water to 55F.  The only other possibility besides the radiator is a timing issue right?

Another would be to run the engine and cooling system - closed - and use the infrared thermometer to "map" the radiators front surface. Looking for hot and cold flow paths that might indicate a blockage. I'm still an advocate of a giving the radiator a nice dose of vinegar and letting it "cook" a while to see what sort of lime you can get out of there.

Your vacuum advance canister - this vehicle has a "Load-o-Matic"? It might be that it isn't advancing as the venturi vacuum rises - could have a bad diaphragm. Try introducing a seperate vacuum source and see if the operating arm moves.

Another idea - check the timing at idle - and raise it manually to about 10°-12° by rotating the dizzy and clamping it. Don't want to drive it this way - simply run a temp test at idle with a bit more spark advance.

I'm going to do the vinegar next.  No this car doesn't have a load-o-matic, it is a manual (does this change the possibility of a timing-related heat issue?).  I will check the timing and see where it is at too.

Pull the radiator and have it cleaned out, flush the block while away and get it over with. Sitting for so long just builds up scale and dirt that goes straight to the radiator cores when started.

Lower center you can see the operating rod of the vacuum pot just between the two point plate springs. It operates on vacuum developed by air flowing through the carb venturi - adds advance as the airflow increases. Test it by opening the dizzy cap and applying vacuum to the pot to watch it move - or not.

The carb vacuum line should show an increasing amount of vacuum as the revs go up - but you may have to have it on the road to test. The vacuum in this line doesn't show manifold vacuum - it operates on the "pitot tube" principle of air flowing past an orfice.

Well if the radiator should be able to flow enough water to never back up out the filler then the radiator is definitly plugged up.  Becuase if opened my spigot all the way when I was doing my expirement, water would start to overflow out of the radiator filler.  It just couldn't handle the hose flow on full blast (I don't have very strong water pressure).

Bill, I hope you're right that I just need a "flush" or as Talkwrench says a "pressure flush".  Are these services that any radiator shop will offer?  Can anyone describe what is involved in these services?  I'm always nervous that I'm going to pay $100 to have someone else run a hose through my radiator when I can do that at home for free.  Do they use chemicals and a special machine or something?

Also Bill you say "flush the block".  I know I asked about this before, but what is involved in the flushing the block?  Just stick  hose in the thermostat housing opening and run water through the engine and let it drain out the bottom (with the engine not running of course)?  Do I use vinegar or something else?

I think the full flow hose through the radiator comment - refers to an open lower rad hose - not the little spigot. Mine won't do that either.

The vinegar treatment - will do wonders for both the block and the radiator - just be persistent.

Many of these outfits (old orignal stockers) have suffered from the retarded ignition - I'd still recommend setting up the advance at idle to see if it does you any good (while circulating the vinegar).

When I referred to the "spigot" being fully open I meant the spigot on the side of my house controlling the water flow through my garden hose.    The lower radiator hose was connected to engine and the engine was running, the little spigot on my radiator was closed.  The upper radiator hose was clamped to shop-vac extension and was pouring into a bucket in front of my car (see pic below).  I plugged the upper hose connection on the radiator by zip-tying a blue latex glove over the connection.  How about in that situation?  Do you think the cooling system should've been able to take in the full flow of water from my garden hose?

No, it wasn't raining.  The hose water that would overflow the radiator filler was spilling onto the fan and flinging all over!

Big6ft6 (8/29/2011)

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Oops , yes my car has a vacuum pot on the distributor.  Thanks for the education!

Bill, I hope you're right that I just need a "flush" or as Talkwrench says a "pressure flush".  Are these services that any radiator shop will offer?  Can anyone describe what is involved in these services?  I'm always nervous that I'm going to pay $100 to have someone else run a hose through my radiator when I can do that at home for free.  Do they use chemicals and a special machine or something?

Also Bill you say "flush the block".  I know I asked about this before, but what is involved in the flushing the block?  Just stick  hose in the thermostat housing opening and run water through the engine and let it drain out the bottom (with the engine not running of course)?  Do I use vinegar or something else?

Nate, i was actually referring to sending rad out and have the lower tank removed , dipped in chemicals, usually rods are pushed through each core to remove stubborn debris, tank refitted and pressure tested, it is a normal procedure. While thats away, flush the block with hose through all openings in turn. At least you know the rad is unblocked and block is free as possible from junk and system should work efficiently.

If the thermostat was in place during your flow test, then the water would back up and come out the filler neck.  If you had no thermostat, then you really do have a restriction, probably the radiator as others suspect.

Marvh, that collapsing hose is often from no thermostat at high speed, causing a partial vacuum behind the flow and has been cause of many high speed over heats also. good point.

With little or no budget money - I'd still try the vinegar first....

I called a radiator shop in Madison today to ask about "rodding" a radiator and the guy wouldn't answer me.  Instead he told me to feel the radiator when the engine is hot to see if there are cold spots, then he also said to pull both hoses, put my hand over the lower hose opening and fill it with water.  Then quickly remove my hand and he said the water should shoot "straight" out, not fall like a water fall.   If it doesn't shoot out then it is clogged.  All good advice that you all have already told me and I plan to do, but didn't answer my question about rodding.

I asked again about "rodding" and he again didn't answer, just told me to feel for cold spots and also check my radiator cap.  I can't quite figure how a malfunctioning radiator cap could cause a car to overheat?

I've been keeping an eye on the lower hose, the spring is good enough that I can't collapse the hose with my hand, so I don't think the hose is collapsing.  Maybe tomorrow night I'll get a chance to feel for cold spots, then I'll run the vinegar through too.  See what happens.

In the morning, I'll hook up the shop vac attachment and garden hose and run her through with well water.

I disconnected the hoses to the heater core and bought a new hose and just bypassed the heater core so I can clean that separately.  Here is what  I found in the original heater hose when I cut it off my poor cooling system!  The hose on the engine side of the manual valve was literally solid with blue-green goo!