Coolant loss

[Ryker]

I saw a recent post about this but I think mine is different. I replaced the radiator in my 8v71 in my GMC 4905 and since then I lose a couple gallons of coolant about once/month. The low coolant alarm goes off, and I now know that is 2 gallons low. I can't find a leak, so is there a chance that it is somehow burning off or evaporating? I ask this because I recently noticed white smoke at start-up, and even when warm, I can see a little white smoke when I step on the gas. The engine was rebuilt about 10 years and 60,000 miles ago.

[richard5933]

Have you checked your oil level? The missing coolant may be finding its way into your engine oil. Is the oil milky? You can have it tested to be sure there is no water in it.

Did you replace the radiator due to an overheating incident? If so, that might be an indication of something inside the engine with a problem. There are others on this board with much more knowledge about this that will join in.

[Ryker]

I did check the oil. It does not burn much oil at all and it does not look milky. I replaced the radiator because I went over a bump and destroyed it. The fan blade went into it and cut a few lines and I saw coolant blowing out so I turned the engine off within about 2 minutes and before it overheated. I've driven it in over 100 degree heat and the temp gauge never goes above 180 degrees. Kevin suggested that the white smoke might be a cracked or leaking injector sleeve but that was in reference to the white smoke. I did not ask him about the coolant loss yet. I feel bad peppering him with questions!

[Geoff]

My Detroit started smoking white at startup and leaving a film of unburnt fuel on the back of the bus and it turned out to be a broken top compression ring on one clyinder.

It sounds like your cooling system is leaking externally rather than an injector tube which would put coolant in your oil.

[richard5933]

When you replaced the radiator, did you close the valves to isolate the front of the bus from the engine compartment? Or, did the coolant leak out before that was done?

There is a huge amount of coolant in the front loop of the bus, going to both the main HVAC heater core as well as the front defroster core. On the way to the front the coolant goes through the water modulating valve and the coolant circulating pump. On my 4108 these are both located in the compartment with the OTR a/c condensing coil.

To properly refill the system it is imperative that the complete loop be bled. If this is not done, there will be an air pocket up front. This could be what's happening - as you run the bus some of the air pocket is being filled with coolant. When my system was opened last spring the front loop was not properly bled, resulting in a huge drop in coolant once the coolant made it to the front. My low-coolant light went on, and it took about 8 gallons to refill it.

A potential casualty of running the system low on coolant, especially if there is an air pocket in the front loop, is burning up the seal in the coolant circulating pump. This seal is lubricated by the coolant, and it only takes a few minutes of running it dry to have the seal fail. Rebuild kits are available, but it's a major PITA to get to it and do the repair.

Of course, if your circulating pump has a bad seal, this could be the source of your leak. The pump runs with both heat and a/c use. You also could have a leak in the front of the bus at the defroster heating core, or in the main heater core which is located towards the front of the bus in the center. And then there is the length of coolant lines running from the engine bay to the front of the bus. There should be a plywood cover which you can remove in the very front bay on the curb side of the bus (the bay that uses rubber hold-downs.) Removing this cover will permit you to get a really good look at the heater core to check for leaks.

Some of these leaks are difficult to find, so get out your strongest flashlight and start the hunt.

[Ryker]

Thanks for the detailed response, Richard. I did not close any valves but I had Ted in Williams replace the radiator, and he knows what he is doing. I tried to get ahold of him to ask him about it but he no longer answers his phone or emails, so I hope he is ok. I know he is getting older and his health may be failing. It would be nice if the system is still filling as I drive.

As an update, we drove to San Francisco and back and the level did not go down at all! So maybe it is filling up through the system and pushing some air out. We are taking another trip this weekend, so I will keep my eye on the level to see if it continues to hold. It is definitely still blowing white smoke at startup.

Looking for the leak today, I did discover that the coolant is hooked up to one of the 3 hot water heaters, so I guess this is how they ran the bus in Canada. I keep learning new things about this mystery bus. I also have no idea how to get heat in the front of the bus, so maybe something is closed off. I do not have any OTR heat or AC, or even fresh air. 

[chessie4905]

Is the heater core behind the center of dash? If so, there is a screw head looking at you through sheetmetal dash. It is a bleeder screw to remove air from core. Below this core should be two blower moters mounted in a vee configuration.

[Geoff]

I'm wondering if Ryker has a working booster heater pump to push antifreeze/coolant to the front of the bus, if not, that would explain a lot.  In fact, that could be his whole problem.  If the booster pump is working it can bleed out the air without having to crack a line-- they are that powerful.

[richard5933]

...Looking for the leak today, I did discover that the coolant is hooked up to one of the 3 hot water heaters, so I guess this is how they ran the bus in Canada. I keep learning new things about this mystery bus. I also have no idea how to get heat in the front of the bus, so maybe something is closed off. I do not have any OTR heat or AC, or even fresh air.

The coolant in the hot water heater is probably going through an exchange loop so that you can make hot water while driving down the road.

You may not have OTR heat or a/c but still have the defroster core. It is located in the front center of the dash. If you still have the access panel on the dash above the stairs, you should be able to see the end of the defroster heat core and the petcock for bleeding it.

I'm wondering if Ryker has a working booster heater pump to push antifreeze/coolant to the front of the bus, if not, that would explain a lot.  In fact, that could be his whole problem.  If the booster pump is working it can bleed out the air without having to crack a line-- they are that powerful.

The pump is powerful, but only if it has liquid in it. The seals in these pumps can be ruined if run dry for more than a very short time.

How far forward are you able to trace the coolant lines? Looks like you know that there is a loop going as far forward as the hot water heater. Do you see any signs of the copper lines further forward? What about in the OTR a/c bay? Is the pump still there? What about in the dash defrost area? If you have access to the ceiling in your baggage bays, you can pull the cover on the tunnel and see if the copper lines are still there, and then you can check to see if they are carrying hot coolant. If they are there but not getting hot, then perhaps the valves on the engine bay firewall are closed. There should be two valves there. If they are closed, be prepared - they could have been closed due to leaks in the areas forward of the valves.

[Ryker]

Oooh weee, I have my work cut out for me. We are taking a trip tomorrow evening through the weekend, so I will not have time to go over anything until the following weekend. Thanks again, everyone, for all of the ideas.

[richard5933]

Have a great trip. Bring along some coolant just in case and check your level before starting each day just to be certain.

[Ryker]

Well, that was easy. I parked on blacktop and noticed a coolant leak. It was the large hose at the bottom of the radiator. I know Ted was feeling weak when he replaced my radiator, and the clamp was just not tight enough. I checked the others and tightened a few. No leak! One more thing to check off my long list. I still have to go through all of my coolant pipes to determine what is open and closed.

As an aside, I replaced another bay door rubber hinge with the metal hinges from Ed. I have to say, these are slick and everybody should know about them. Will last forever but also so much easier than trying to string that rubber hinge into place. My first hinge took me awhile but I did this one in about half an hour.

[Ryker]

Quick update on the smoke when starting. It finally got cold in Northern California so yesterday I tried out my block heater. I had it on for about 8 hours. When I went to unplug it, I could feel the heat from the engine, so it was doing a great job warming things up. When I started the engine, it fired immediately and had very little smoke! I was happy to see that, of course. So my engine smoke was just as the weather was changing, even though it really was not that cold here, it still made a difference.

[dtcerrato]

Sounds like your rings are getting tired. BTDT but they'll continue to run run run.