Hi,
I am new to this forum but no stranger to the slant six engine. I have somewhat of a mystery on my hands here though and would appreciate a few ideas on where to look next. I will attempt to be brief.
I have a 79 D100 with a 225. My engine is out of a 78 and was rebuilt 6000 miles and 2 years ago. the head was also rebuilt and came from my original 79. I have eliminated virtually all of the emissions on this thing (smog pump, Catalytic converter etc.) There are still some remnants of the emission system plugging up a few holes. I mentions these remnants because I suspect that my problem may have something to do with them. Other than the slight mods to the emissions, the engine is totally stock and still running the 1bbl carb, stock intake and exhaust manifolds.
The problem I am experiencing is that the truck runs hot at high speeds/RPM's. At idle, it will stay at 185 all day. The faster I drive the hotter she gets. It will run about 235 degrees at 65 or 70 MPH (in third gear of course, tranny is 3 on the tree). I replaced the thermostat with a 185 degree, thinking it might be stuck open and not allowing the radiator to hold coolant long enough to cool. I was running about 17 degrees BTDC. So I tuned it to the recommended 12 BTDC and fattened up the fuel mixture on the carb thinking I might be leaning out. No difference at all. I readjusted the valves to .010/.020 eliminating that as a possible cause. I replaced the water pump and flushed out the entire coolant system (running out of good ideas at this point) and again... no difference. The only thing that will lower the temp at higher speeds is dumping the heater core into the system which drops the engine temp from 235 to 215. Unfortunately it raises the temp in the cab to about 210 degrees as well makes driving this thing less than fun.
Being that the radiator is only 2 years old and clean as the day I installed it, coupled with the fact that the entire cooling system is brand new, I can't see the problem being there. I don't believe the problem is with fuel delivery/mixture either, the truck just runs too damn good for that. I am now starting to look at the exhaust as the possible culprit. This exhaust system was definately designed to run with the emission system installed. I will admit that some of the stuff I tore off I can't even name. If it didn't help the engine run and could be taken or cut off...it went. The smog pump had some pipe that went into the downpipe and I welded it closed. As I mentioned earlier there some remnats. Specifically I am referring to a heat valve thing that is located in the top of that stock manifold and has some counterbalance weight that opens and closes the valve depending on engine RPM (or so it seems to me). I also left the EGR because it seals a hole on the intake, or more specifically, where the intake and exhaust manifolds meet. I think maybe one or both of these parts may be interfering with the exhaust flow at high RPM's and causing the head to heat up.
I am afraid I failed at my attempt to be brief (sorry about that). I am hoping that someone out there may have encountered a similar situation or has some idea of what could be causing this slant to act like air cooled VW instead of the heartiest American made engine ever built. Any ideas/input is greatly appreciated.

Thanks

Even though the radiator looks clean, it might have sludge in the bottom tank that is reducing flow. I would pull the radiator, and have a shop flow test it. Reasoning that the additional heat rejection of the heater core helps quite a bit.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I agree with the above. Just cause radiator is new doesn't mean it's ok. Hard/mineral water dicks up a system real quick! I would also flush the snot outta the whole system before running to a radiator shop. Drain the system and run a couple bottles of radiator flush with water for a few days then flush, back flush, flush again. If still nasty stuff comes out, go buy more flush. Then drive for a day with just water to see how it behaves. That way you don't waste antifreeze if you still have a problem. If all is ok, drain as needed then fill with required antifreeze. Good Luck

I suppose that flow testing the radiator will definately not hurt. I have already power flushed it with one of the prestone kits that allows you to tie a garden hose to the heater hose and run fresh water through with the engine running. I ran it until I got nice clean water running for 10 minutes. The only question I would have is: If the radiator was clogged or obstructed, wouldn't the engine run hot at idle as well? I suppose it is possible for it to be just limiting the flow in such a way as to cause these symptoms but I have never run across this in 20 years of wrenching on cars.
I do appreciate the input and will get this radiator flow tested. I will post the outcome as soon as I can the truck in and out of the shop.

From reading your post it sounds like your EGR is Non-Op.


Try something. Retard your timing five or six degrees and see if it cools down.


CJ

Edit: Brain damage. Still, I'd back off to initial of zero and see what happens.

Engine heat-up that increases with vehicle speed is usually down to a water flow problem, a heat-rejection problem, and/or an exhaust flow problem.

Water flow problems can be caused by a clogged radiator (even if it's relatively new), a block with mud built up in it (remove the freeze plugs from the side of the block, scratch around in there with straightened-out coat hanger wires, and flush the crud out through the detached lower radiator hose), a lower hose that's collapsing at higher engine speeds, or a faulty thermostat.

Heat-rejection problems can be caused by insufficient radiator heat-transfer capacity (because the radiator is poorly specified or built, or because it has deteriorated, or because its front surface is clogged with bugs and road dirt). Such problems can also be caused by improper timing advance at high engine speeds. Insufficient advance (timing too retarded) will cause overheating without pinging. Excessive advance (timing too advanced) will cause pinging and overheating. You'll want to check and make sure the distributor's two advance mechanisms (vacuum, mechanical) are working correctly to advance the timing in response to increased engine RPM (mechanical) and vacuum. Sounds like your base timing is set correctly at 12°; you should not need to retard it significantly unless disabling the EGR has caused a great deal of pinging, in which case try 10° instead of 12°. Also keep in mind the camshaft timing. If the timing chain has a lot of slop in it, the cam timing will be off (retarded) which will not only kill power but also can cause overheating.

Exhaust flow problems are caused by...restrictions in the exhaust system! Collapsed baffle in the muffler, manifold heat control "heat riser" valve stuck in the "heat on" position, crimped pipe somewhere along the line, etc.

The 185° thermostat is an interesting find; I normally see them offered at 160°, 180°, or 195°. My pref is usually a 180° Stant Superstat # 45358.

Your mixture adjustment on the carb really affects only idle operation, not the high-speed operation at which you're getting overheating, so you might as well set the idle mixture correctly and save your gas money and spark plugs.

Your manifold heat control valve is working if you can see the round counterweight rotating as you rev the engine. Leave it alone. The EGR valve isn't interfering with anything. You can leave it alone, too, aside from removing and plugging the vacuum hose that goes to it.

I suspect in the end you'll find the radiator isn't up to the job you're asking it to do, but before reaching that conclusion, there's one more thing to check: Is the engine fan installed the right way round? If it's on backward, it will be trying to push air through the radiator from back to front, and once you reach high enough vehicle/engine speeds, the rearward flow from the vehicle's motion will fight the forward flow from the backward fan to the point that almost no air will flow past the radiator in either direction!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I am not sure of the different radiators offered on the Dodge trucks, but I'll say this. I had a mid 70s Dart w/o a/c, and it had a smaller radiator (maybe 20 inches wide) as opposed to the 23 inch wide radiator offered on the air conditioned models.
My car always ran hot at high speeds, and the only thing that ever solved it was installing the slightly wider 23 inch radiator from an a/c car.

After that, the car always ran cool and I never had problems like that again.

The fan does need to be installed correctly, but it will not push the air back to front if it is on backwards. It will still pull, but very inefficently.
PS: I just went out to the shop to confirm this statement.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Depends on the fan blade design. Many cooling fans won't push air if installed wrong way round, but some of them will. I'm thinking of two particular variants of the cheap/basic 4-blade fan used on a lot of slant-6s. The one that basically consists of just two crossed, bent "straps" of metal. There were about four different variants of it, of which at least two will push air if installed wrong way round.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Wow!! lot's of ideas...Thanks
I have checked the fan (flex fan by the way) and it is on correctly and pulling great air. The vacuum advance seems to be operating correctly but I do not have a timing light that will measure out at those higher RPM's. All I have is an inductive light, so when it advances so far beyond the graduated marks on the harmonic balancer I can barely guess. However, I do not think that it is malfuctioning. Out of all of the ideas so far I am leaning towards a poor radiatior design. It appears to me to be a bit undersized for the job. It is just a little dual core. Of course, I am no engineer so I can't imagine that Dodge would put too small a radiator on a truck this heavy.
Has anyone heard of having to go to larger or triple core radiators for these? I neglected to add earlier that I did change the rear end in this truck to something higher geared to give it longer legs and improve highway gas mileage. I am also running 31 inch tires which is demanding a little bit more from the stock engine. I have shopped around a little bit (mainly at regular parts stores) and only one radiator seems to be available. As always, I appreciate any and all info.
Many thanks for the help so far...

Run it until it warms up and shut it down. Before it gets a chance to sit and percolate feel around the radiator for any "cool" areas. If the radiator is blocked, the restricted areas will be colder than the rest of the radiator. MBF

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Good gun control is hitting your target repeatedly

Ahhh...but Dodge didn't. You did! The quality of aftermarket parts is all over the map. There's nothing that can't be made cheaper and nastier, and that is the rapid and accelerating trend in auto parts these days. I've had many radiators upgraded over the years to 4-row (or 3-row high efficiency) cores. If you have a good radiator shop in your area, they can handle the job.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Those are the kind I checked 65-66 "A' body slant six 4 blade. Even if you install the blade backwards, the leading edge is forward of the trailing edge, and the rotation of the engine did not change. the only thing that changed is the "angle of attack". Instead of "scooping air (like a cupped hand, in swiming) it is pushing the air, with what was the backside of the blade.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I gotta go with Charlie on this one.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Different variants, different blade shapes. The '65-'66 A-body units probably would behave as you say, when I think it over. Some of the other variants (the one with the notched corners, the one with the rearward-bent ends) behave otherwise. I'm sure you observed what you say you observed and have no reason to contradict you; I played with different fan blades. :shrug:

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一期一会
Too many people who were born on third base actually believe they've hit a triple.