I'm at a loss on this one and I need some new ideas. Been fighting this on my Ramcharger since the beginning. 1985 4wd with a 318/727.

Plain and simple, it won't control the water temp on the highway. It will idle at 160° until it runs out of gas, you could drive it from NY to LA as long as you never got on the interstate. But start pushing the speed to 65 and beyond and that temp needle will slowly climb and climb until you back it down to 55 again.

First of course you say this is classic symptom of a plugged up radiator. Second you think maybe there is an airflow problem. After that you start reaching for ideas. I'm well past all of that, well past the "replace everything" stage. I'll summarize with bullet points.

- new 3 core radiator (replaced twice)
- new hoses (lower has the spring in it to prevent collapse)
- thermostat (replaced twice)
- water pump
- all air baffles in place
- engine is clean, no dirt/grease blanket etc.
- coolant is perfect color, nice and clean, so no crud is circulating in it
- no water in oil, no oil in water, no exhaust gases in water, no leaks anywhere inside or out
- runs perfect


Basically I'm down to replacing the engine, but I refuse to believe there is anything wrong with this engine, I have to be missing a clue somewhere. I'm serious, you could idle forever in traffic on a 100° day and barely crack the thermostat open. You could drive around the world at 55 MPH. Oil pressure etc. is perfect. There is no way this engine needs to be replaced.

Any other ideas?

What fan assembly and you running. Is it a clutch type? Also how far into the shroud does the fan extend?

When I lived out in Pa. I had wrecked my then-new car and needed a bang-around. I found a `75 Dart (this was in `94) that had only 32K on it. Nice clean 4 dr. 6 cyl, A/C, automatic Brown & tan. The original owner, she said "it's never been out of Lancaster County. Never run on the highway". First time I attempted to drive back to NY with it to visit family I had the SAME EXACT CONDITION and eventually replaced exactly the same parts, PLUS I reverse-flushed the cooling system. Still overheated. At that point I wrote it off as sediment in the block from the car sitting that was fused in there…. and it wasn't until recently that I ran across the same condition in a late model Infiniti when I was still doing that. Here's what I learned.

When I reached-out to the factory service hotline for repair incidents similar, and what the resolution was, I was told that once a block is scaled-up around the cylinders it will never transfer heat correctly back into the water jackets. I had to replace the short block in the FX-35 to fix the overheat problem. We threw a whole bunch of parts at it too going from diagnosis to guessing. Is this a vehicle you've owned for a while? Or is it a recent addition to the garage? Granted, the Infiniti was aluminum, but it sounds like your gakked-up around the cylinders…..

Has it ever boiled over? Maybe there is no problem at all. Who is to say your temp gauge is working properly? What temp does it warm up to at 65mph before you back down the speed? What it the highest temp you have seen?

Might be leaning out as you press into the higher speeds. Does it miss at high cruise? faint lean miss? a lean miss also cause a slight hesitation as you press on the gas at a stop sign.
You may have to rejet the carb a little.

Vacuum leak?

Have you tried running the heater full blast while it's over heating? Does that help cool it down or does it even blowing hot air? That can give you a hint at what the problem might be.

thanks for the replies, I'll try to address them all

- stock clutch fan and shroud, replaced the fan clutch once (forgot that on my original list)

- have tried several different carburetors (not because of this problem, just because I have other 318s and carburetors get swapped around during various adventures) and the problem is always unchanged. So things like air/fuel mixture aren't real logical unless every 318 carb I have has the same problem, also unlikely cuz they run the gamut from 60's Stromberg to 70's Carter to 80's Holley models. BTW I have also been all through the ignition system and settings, checked for vacuum leaks, etc. The truck runs absolutely perfect, no hiccups, issues, weirdness of any kind. Starts instantly, runs perfect.

- it has always been this way. I bought the truck in a dilapidated state and restored it. So I don't know if it was going on before that.

- I have verified the aftermarket gauge reading two ways- with a Snap On thermometer in the rad neck and also with an infrared temp meter. It's right.

- basically, if you are driving around town or sitting in traffic it will barely hang out at the thermostat setting of 160°. If you start running down a two lane highway at 55-60 MPH it will climb a bit and stabilize around 180°. If you get on the interstate and run with traffic at 65-70 MPH it will slowly climb and climb and climb, I've let it get as high as 240° before I ran out of nerve and backed it down. If you take it down to 50-55 MPH it will come back down to normal. Again, jump out and shoot a few spots on the block with the infrared meter and it will be darn close to whatever the dash gauge says.


I've driven Chrysler products with every type of malady and in various states of disrepair, I've never seen something like this that had no reason to complain and still does. A d@#n 318 like this should be able to go to the moon and back. Frustrated.

How hot does it actually get? What gauge are you using? Factory or aftermarket? Where's the gauge hooked up...cylinder head,intake manifold? What does the timing curve look like...retarded timing will make heat. I had a BB Suburban I battled years ago with a temp issue pulling a trailer...it turned out timing was f'd up under load.

has the timing been checked, initial, mechanical, vacuum, and total ???

Restricted exhaust???? heat riser not opening all the way, cat plugged (if it's still there), Internal baffle in the muffler, or restricted in some other way

Converter slipping (long shot)

I am assuming if it has an a/c condenser that it is not plugged

My guess: youre not running a vacuum advance and don't have enough timing.

What is the timing set at?

Its a long shot, but what sizes are the crank and WP pulleys? Any chance they got swapped around and the water pump is turning too slow or way too fast? Also agree double or triple check timing and make sure the vacuum advance is functional.

Have you popped a freeze-plug and took a look inside???

I had the same issue with my Savoy and it turned out to be the pulleys weren't running the pump fast enough on the highway. I had underdrive pulleys on it from when I was racing it a lot.I got a set of repro pulleys from 440 Source and "PRESTO" an all stock cooling system with a 5 blade clutch fan cured the problem.Now instead of running 230 on the highway it stays around 190
Gus

I had this problem 7 years ago and then again this summer.My belt running the water pump was loose and when on the highway it was slipping and not turning the pump,sounds weird, but it was true!!!

Lots of good replies so far.
I was troubleshooting a '66 Valiant that had a surging problem at speed. It turned out to be a plugged fuel tank vent line. A whole different vehicle once it was fixed.

""have tried several different carburetors (not because of this problem, just because I have other 318s and carburetors get swapped around during various adventures) and the problem is always unchanged. So things like air/fuel mixture aren't real logical unless every 318 carb I have has the same problem, also unlikely cuz they run the gamut from 60's Stromberg to 70's Carter to 80's Holley models.""

Back when the 318 carbs were designed and tuned from the factory, I would guess that there was a different type of fuel than what we use today. If you tried several different 318 carbs, I would assume that they would all give the same results.

Todays fuel (E10) needs a richer A/F mixture than when these 318 carbs were designed. If the engine starts to warm up at 55-60mph, then gets even warmer above that speed, then I would at least try to richen up the jets to see if that helps out the temp at those speeds.

I have had to richen up my A/F mixture just over the last couple of years. I am assuming that this is due to change in the fuel at the pump over the last couple of years. I can't imagine trying to run a stock 318 carb on todays fuel without changing the carb setup.

I love the toughies . I gotta stick with the basics: not enough water flow or not enough airflow. I'd make sure there is adequate airflow thru the rad however way you choose to check that. I'd toss the stat for an hour test which wont hurt the eng it being gone for an hour. I'd double check that lower hose/spring & you could block the rods up so it's on the power circuit just to elim AF ratio/potential vac leak. You might pressure check the cooling system when hot to see if there is a minor pinhole leaking combustion into the coolant. Keep us posted! With it going up to 240 there has to be a severe coolant or airflow restriction showing up at higher RPM when the eng is producing the most heat & that is when the inadequacy shows up. I have the same vehicle ex it's 2wd. You wouldn't happen to have a shop manual or a wiring diagram for it would you? Gas gauge is non op

Can you post a picture of your belts and fan.

I'd make sure the rad hoses aren't being sucked flat. Spring in the lower hose?