Overheating 345? Help!

Brian K

Brian K

Member
Hi!

I'm almost embarrased to post a thread about an overheating engine....you'd think it's a pretty easy problem to find and correct....yet here I am. Geez.

'79 Scout, 345. It used to always run right below even the "range line" on the gauge. Suddenly, overnight (it seemed), it started riding in the middle. So, I:

1.) changed the sender as I thought it was strange -- the cooling system was otherwise perfect. (didnt' help.)
2.) changed the thermostat to a new robertshaw style (the old one was fine.)
3.) removed and had the radiator "rodded out."

put it all back together, "burped" the coolant when adding it, and still no better!

Gauge runs very hot and the engine is clearly hot as it starts to pop the pressure safety on the radiator cap.

Any ideas? Thanks!!
 
Robert kenney said:
fan clutch?

Does it run cool on the highway and hot in town?
Click to expand...

Hey Robert! Nope. Hot all the time. Didn't matter if I was on the freeway with lots of airflow or none at all. Leads me to believe it's not airflow or a problem with the thermostatic fan, but it's got to be coolant flow somehow.

Can a water pump, based upon it's design, go bad without ever "weeping" out the weep hole? It's the only thing I haven't pulled.

Thanks!
 
If its the steel finned water pump, it could be rusted away, which makes bigger gaps & tolerance's for water flow.is it original wpump ? Are you getting bubble's in the overflow tank /Jeff ( get a cast iron finned wp, if you can find 1.
 
Have you checked the vacuum line to the vacuum advance can on the distributor? If it fails, the ignition timing won't get the extra advance at driving speeds - in effect, the timing is retarded by the amount normally supplied by the vacuum advance. Also check the mechanical advance of the distributor. Retarded timing can cause the engine to overheat.
 
So if I read your first post correctly, the temp is at the middle on the gauge (not hot really) and you have the pressure cap blowing off at that temp?
If you are using a coolant recovery bottle and it is working correctly the cooling system will be solid coolant after several heat cycles. So as the system heats up the water expands and the cap allows the extra water to push out and into the bottle. That coolant expansion easily reached the cap pressure. This is totally normal, but once the engine reaches temp the system will stabilize for the most part. If you continue to see bubbling or a constant flow of coolant into the bottle you could have a problem. Basically something is displacing the coolant and that could be combustion gasses entering the coolant system.

If so you are probably looking at a combustion leak of some sort.

Don't jump to any conclusions yet. Run a couple of tests.
Try to verify the true temperature with a ir thermometer at the thermostat housing or mechanical gauge.
Them run what is known as a block check or combustion gas presents test. Napa sells them. Fairly simple test.
 
Thanks for all the tips. I know that water pump has been on there a long time and it's on a truck that isn't used that much. I'll yank the thing and report back.
 
Several people have suggested a combustion leak. For around $25 you can purchase a tester and you'll know in about 10 min if the head gaskets are tight. I've had 3 different 345's leak into cyl #5. It's best to catch it before you need to bore the engine.
 
Well, I yanked the water pump. It looks perfect. It's got the better cast iron impeller, too. I looked very closely at it and it also looks like there is no way that the impeller has ever rotated separately from the shaft. Their is plenty of gunk in the seam to suggest that.

So. I guess I put everything back together and get a combustion tester. If it shows positive, can anyone recommend a method to determine which head gasket is leaking? Also, is there any sense in just taking off the valve covers and trying to retorque the head? Or once the gasket goes, it's gone?

Interestingly, this engine was rebuilt ten years ago or so, it's only got 10k miles on it. It was rebuilt initially due to an overheat problem which "shrank" a piston and caused a knock. I'm wondering if the heads were properly machined flat prior to rebuild.

Thanks! Brian
 

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You can now accomplish a "static" differential-pressure compression check to each cylinder to determine which cylinder(s) is bad.
 
Brian, don't take offence to me explaining the following if you know. It's much more for people who are not familiar with terminology and processes.
So let's explain what to look for while doing the leak down or differential compression test.

First we might explain what a dct is. Basically air from your compressor at a regulated pressure @ 100 psi for this discussion, is forced into the cylinder while at tdc on the compression stroke through a calibrated orifice. On the cylinder side of the orifice there is another pressure gauge that reads the pressure the cylinder will hold. The air that enters the cylinder will find the leaks in the cylinder head gasket and valves. Example 100 psi in and the cylinder will only hold 90psi. This is a 10% leak down. While the cylinder is being pressurized you can listen for where the 10% is going. Either the carb for an intake valve, the exhaust for an exhaust valve the oil fill for rings and with the rad cap off bubbles in the radiator or a rise in the level of coolant.

A head gasket leak May be subtle and hard to see with the dct.
A combustion gas test is better. They are pretty much absolute. Very little in the way of gray areas.

A hg that is passing combustion gasses is gone once that happens. The hot gasses erode the gasket and it will never seal again. If you can see what type gasket was used it May help determine the issue. Steel ones are more sensitive to head warpage.
 
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Robert,

thanks. I appreciate the deeper explanation for sure. While I'm waiting for my shipment of new hoses and belts, I took all the plugs out last night and did just a crank-style compression check.

All cylinders came in at 125-127 except for #6 which came in at 120. For the hell of it, I'm going to go repeat the test on #6 just to be sure.

Is that enough of a differential in compression in one cylinder to arouse suspicion?

Regardless, I'm now going to yank and clean and inspect the coolant tubes and reassemble the whole shebang. I'll then proceed to the coolant test I suppose. The head gaskets are the composite type, not metal.

More answers forthcoming, I suppose. Thanks again!
 
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I have to ask for clarification again. I might have missed it but here it goes.

When you say "hot" where is that on the gauge? The middle?
The middle on the IH gauge has been about 180 on my 2. You're
digging around for a problem that May be nothing.

Do you think there is a problem with the tubes? Simply no way there could be. If they aren't leaking they are fine.
 
Brian k said:
well, I yanked the water pump. It looks perfect. It's got the better cast iron impeller, too. I looked very closely at it and it also looks like there is no way that the impeller has ever rotated separately from the shaft. Their is plenty of gunk in the seam to suggest that.

So. I guess I put everything back together and get a combustion tester. If it shows positive, can anyone recommend a method to determine which head gasket is leaking? Also, is there any sense in just taking off the valve covers and trying to retorque the head? Or once the gasket goes, it's gone?

Interestingly, this engine was rebuilt ten years ago or so, it's only got 10k miles on it. It was rebuilt initially due to an overheat problem which "shrank" a piston and caused a knock. I'm wondering if the heads were properly machined flat prior to rebuild.

Thanks! Brian
Click to expand...

Wow that's cool you have the cast iron impeller.

See if you can borrow an irgun they are helpful in know the temperature.
 
Robert kenney said:
I have to ask for clarification again. I might have missed it but here it goes.

When you say "hot" where is that on the gauge? The middle?
The middle on the IH gauge has been about 180 on my 2. You're
digging around for a problem that May be nothing.

Do you think there is a problem with the tubes? Simply no way there could be. If they aren't leaking they are fine.
Click to expand...

All,

I think I figured it out. So I took everything apart. Water tubes, hoses, etc. I'm glad I did. The water tubes at the ends were a bit corroded, the water neck same thing. The hoses were fairly hard. It was time. Fresh water tubes, o rings, hoses, wire brushed everything, fresh paint on the thermostat assembly.

Then time for the rebuild. Good so far.

Until it was time to put the belt back on the air pump. The pulley will literally not move, even with both hands on the thing. I think it's damn near frozen solid. I'm surprised the thing even went around without breaking the belt or causing it to slip.

I suspect it was causing so much drag on the engine that it's my source of the temperature rising. Damndest thing.

I'll finish the re assembly and take it for a spin.
 
Craig said:
wow that's cool you have the cast iron impeller.

See if you can borrow an irgun they are helpful in know the temperature.
Click to expand...

Agreed! I May keep it and take it to a local rebuilder. Those are hard to find anymore. It's in great shape too.
 
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