Strange overheating problem

dfeazelle · 12-20-2020, 01:28 PM

2003 Thomas with CAT 3126 171K miles, had
161K when I bought it as a retired DUI Unit from NC. Was rebuilt at 107K...

When I turn the pump on to circulate coolant for driver heat (while accelerating) the engine overheats. It's fine while idling and will drive for DAYS until you turn the pump on to heat the cab.

Had the tensioner and belts replaced...no help. Had the coolant vacuumed and refilled... no help. That guy turned the valve down to allow less coolant to the front of the bus and thought it was fixed... it's NOT!

I've spent a ridiculous amount of time researching but really don't know all the right terminology/lingo so I came here to BEG for help. I'm 3 years in and it has been 1 step forward and 2 steps back from the moment I started. It would be nice to fix some of this stuff!!

Thanks in advance for any suggestions!

Brad_SwiftFur · 12-20-2020, 03:39 PM

My first thought is to wonder is the heater pump is "pumping" backwards, either by being wired backwards, or (more likely) the hoses swapped. It would make sense that it could be pumping backwards and making the cooling system unable to pump enough coolant through the radiator that it over heats.

EastCoastCB · 12-20-2020, 04:09 PM

Unrelated- but definitely check the condition, age, and tension of your water pump belt. Its BEHIND the serpentine belt and easy to overlook. Its crucial.

cadillackid · 12-20-2020, 04:41 PM

both brad and EC bring up great points... on my DEV bus the heater pump was pumping "backwards" when I got the bus.. it was trying to force flow back into the outlet of the engine... it didnt overheat my engine but my heat didnt work..

and yeah that little tiny belt behind the main pulley ive seen them loose many times

dfeazelle · 12-20-2020, 05:17 PM

Thank y'all! The "local" diesel mechanic did preventative maintenance on my bus recently. He changed oil and filters in the engine, transmission, and generator... replaced the tensioner and both belts. He also put 3 batteries in that I didn't know it needed �� $3,012.00 and a month later I got it back and he was SURE the loose belt/tensioner was the issue but it made no difference. So, I reached out to a few knowledgeable mechanics and they said it HAD to be air in the system. So I bought the vacuum/refill tool, gave it to a moron in exchange for his labor (never expected to need it again). He's the one who decided closing the valve most of the way/restricting the flow of coolant to the front "fixed" it. He claimed to have put a gallon more antifreeze in than he vacuumed out but there is antifreeze all over the engine, motorcycle carrier, and interior of the bus that he tracked in on his ginormous clown feet.
I've had SO much trouble finding help where I am!! I go full time in June so I hope to find plenty of knowledgeable folks wintering in AZ next year to get the million loose ends tied up.

Thanks again!

EastCoastCB · 12-20-2020, 05:59 PM

$3000 sounds like a ton of money for that.

I promise you- You can do all that stuff yourself with common hand tools for like $400.

dfeazelle · 12-20-2020, 06:06 PM

Quote:

Originally Posted by EastCoastCB

$3000 sounds like a ton of money for that.

I promise you- You can do all that stuff yourself with common hand tools for like $400.

It totally blew me away!
My brother was my go-to person to fix anything and he would show me how to do stuff. But I lost him to lung cancer at 45 years old. I watch a ton of videos and take on small projects but there is SO damn much to learn with a bus/rv it's overwhelming!

EastCoastCB · 12-20-2020, 06:09 PM

I could probably walk you through it. None of it is hard at all. You'll get to know your machine better doing it all... Not trying to be pushy. Its 100% awesome you got all that stuff done. Most people do very little to actually maintain their skoolies.

Brad_SwiftFur · 12-20-2020, 10:13 PM

$3K+ for that??? Maybe I'm not up on current prices but it seems to me that was way more expensive than it should have been, unless more work was done that wasn't listed.

The thing is with an issue like yours, mechanics work on multiple vehicles and never really get familiar with any particular one (except the ones they use frequently). You should/will get to know your bus and all its idiosyncrasies, better than any mechanic will.
Now, sure, there are some jobs requiring major tools that justify a trip to the shop, and some of us physically aren't able to do some jobs on our rigs, but many tasks will be far cheaper to do yourself, or shop around (if you can).

dfeazelle · 12-21-2020, 06:40 AM

I'm a few hours away from the bus and might not be home for a couple of weeks.
Sorry if this is a dumb question...
if I reverse the hoses on the pump (or turn it around) and that's not the problem, can it damage anything?

Booyah45828 · 12-21-2020, 11:19 AM

Will it overheat at idle with the pump on? When you say it overheats, you mean it blows the radiator cap right?

Like others have suggested, you likely have an issue with the pump being wired wrong/in the wrong direction. Couple that with air in the system and you're getting your issues.

dfeazelle · 12-21-2020, 11:31 AM

Quote:

Originally Posted by Booyah45828

Will it overheat at idle with the pump on? When you say it overheats, you mean it blows the radiator cap right?

Like others have suggested, you likely have an issue with the pump being wired wrong/in the wrong direction. Couple that with air in the system and you're getting your issues.

No, it'll idle all day long and circulate coolant to heat the cab. I did just have the system vacuumed and refilled and IF he did it right, it didn't fix it.

sportyrick · 12-21-2020, 06:06 PM

As booyah asked is it blowing it's top or could it just be a gauge/pump voltage problem?

dfeazelle · 12-21-2020, 06:31 PM

Quote:

Originally Posted by sportyrick

As booyah asked is it blowing it's top or could it just be a gauge/pump voltage problem?

No, it just sounds an alarm and lights flash that it's too hot and shut down the engine. I turn the pump off (usually before that happens) let off the accelerator and within 10-15 seconds the alarm stops and warning lights go off.

Brad_SwiftFur · 12-21-2020, 08:51 PM

Quote:

Originally Posted by dfeazelle

I'm a few hours away from the bus and might not be home for a couple of weeks.
Sorry if this is a dumb question...
if I reverse the hoses on the pump (or turn it around) and that's not the problem, can it damage anything?

I don't think reversing the hoses can make it any worse than it is now.

bus-bro · 12-21-2020, 09:30 PM

Maybe there's supposed to be an orfice plate in the heater loop, so as to regulate the flow rate?

On my bus the coolant that goes into the heater loop comes from the bottom of the coolant circuit; and comes back and outputs at the top of the engine. There is a pump in-line if needed.

In my way of looking at it, the heat loop is in parallel to the engine cooling loop. Too much flow through the heating circuit might starve the engine loop of cooling.

Then again you're coolant pump could be pumping backwards and be short circuiting the coolant system.

Be interesting to shoot points on the coolant system with an IR gun when things are up to temp. and the coolant pump is on.

Native · 12-21-2020, 10:41 PM

I can sure feel for you on this one. I have been looking for a flow diagram for our bus for a long time. I pulled out the heater loop's water pump years ago and did not note the direction of flow. I have since been looking for the afore-mentioned diagram.

sportyrick · 12-21-2020, 11:02 PM

Your looking in the wrong spot, check voltages on the temp sender and turn on your pump then and look for change. it's not a hot engine, it's a voltage, ground or feedback problem to the computer. It takes time for an engine to overheat, it doesn't happen immediately or cool down immediately as you describe, voltage does though. You should have been using a temp gun to substantiate the real temp when this happens to prove that it's not the engine but another gremlin hiding in the shadows. Looks like Murphy had everyone fooled on this one. It will be interesting learning what really was happening, were sitting on the edge of our seats waiting.

dfeazelle · 12-22-2020, 03:53 AM

Thanks so much for all the input everybody!!
I'll update y'all when progress is made!

Booyah45828 · 12-22-2020, 08:59 AM

Heater circuits are simple. The coolant supply for them will be at the top of the engine, either in a cylinder head or near the thermostat. Hot coolant will then go into the heater, and return to somewhere near the water pump or lower radiator hose. This way the engine water pump can circulate coolant through the heater loops, much in the same way it circulates it through the engine radiator.

If you have this backwards, you'll have lower heat production, and with an electric heater pump you could also cause an overheat because cool/cold coolant will be constantly going past the thermostat. The engine water pump and electric heater pump will essentially be fighting each other.

You can see the electric heater pump on either the supply or return, but typically it will be on the supply because they're better pushers then pullers.

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