Coolant Loss

VerMonsterRV

Gotta Be Nuts
Hi guys, well we seem to be losing coolant. I have spent time working around the engine and have not seen any leaks. I also keep watch beneath the truck for any leaks and so far nothing. I do not notice a white smoke once warmed up ( though I do notice in the cold morningswhen we start up). The engine seems to sit at the same temp with only occasional runs of the fan when warmer out (above 70f under load). Once settled in Guadeloupe N.P. I will tip the cab and try and see any leaks. Any thoughts on how to track this down? We fill the black plastic coolant tank to the edge of the fill (what we understood from the manual).
 

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luthj

Engineer In Residence
How is the overflow/reservoir designed on these trucks? A weak pressure cap and altitude changes can sometimes cause coolant loss through the overflow.
 

Neil

Observer
Is your hydronic heating system sharing the same water or did you keep the circuits separate.

We have a small tube that runs from the top of the radiator into the side of the neck of the filler on the expansion tank. Its about 10 mm diameter. Not sure what it's function is.

The filler cap has two seals with a spring for the lower one. This pipe feeds pressured water into the neck between the seals.

If I fill the system to the max it pumps pressured water into this void and instead of it returning down into the header tank it vents steam out of the cap.

The loss had me baffled for a while.

The solution is that I keep the water level down to a minimum and it doesn't vent.

Changed the cap, it made no difference

Something to look at

Neil
 

VerMonsterRV

Gotta Be Nuts
Is your hydronic heating system sharing the same water or did you keep the circuits separate.

We have a small tube that runs from the top of the radiator into the side of the neck of the filler on the expansion tank. Its about 10 mm diameter. Not sure what it's function is.

The filler cap has two seals with a spring for the lower one. This pipe feeds pressured water into the neck between the seals.

If I fill the system to the max it pumps pressured water into this void and instead of it returning down into the header tank it vents steam out of the cap.

The loss had me baffled for a while.

The solution is that I keep the water level down to a minimum and it doesn't vent.

Changed the cap, it made no difference

Something to look at

Neil
The hydronic hookup is still on the TODO list, though the water to water heat exchanger is already installed.

I think we may be seeing what you are talking about. Each time I check the coolant there is a bit of coolant in the between seal area. We do smell a bit of coolant while driving, I think coming in thru the heater. Since that bit takes cabin air near that vent pipe that would make sense.

As far as altitude, we are up and down now, started at sea level and was up to 5,000 feet.
 

loonwheeler

Adventurer
I found the same issue with our truck, no matter how often I would check the coolant tank the levels would seem to settle at or just below the MIN level. I hypothesized that with the engine circuit, hydronic heater, calorifier, and heater matrix installed all on the same loop, the system volume had increased so much that the OEM coolant tank could not handle the expansion volume of fluid coming from ambient temps and increasing to full operating temperature (~83 C).

My solution was to add another coolant tank with the fill cap / overflow a the same height as the OEM coolant tank to add negative volume to the system. Since install, I have not had these issues and the coolant level stays near the half way mark between MIN and MAX fill.

To be honest, I never estimated the increase in system volume nor did I do the simple math to calculate the theoretical change in volume with different temps, but the solution did work well for the truck with the two circuits combined.
 

eilatmar

New member
you can disconect the heater pipes ans see what hapens. mabe you have a small leake from the heater radiator.
 
What vehicle is it? If it’s a 2005-06 U500NA it’s a leak in the EGR cooler. The item was redesigned with a different part number after numerous ones sprung leaks.
PM me if that’s your vehicle.
 

VerMonsterRV

Gotta Be Nuts
The truck is a 1988 1120 AF with the OM366LA engine. We plan on being in El Paso in a couple of days and I hope to take a look then.
 
The white smoke on startup suggests at least the possibility of coolant getting into the combustion chamber. Cooled EGR is a common cause but not the only cause.
 

Neil

Observer
I am not sure that this engine has an EGR valve. Sounds a bit too technicalit advanced for this era of mercedes.

Might be wrong , I am only comparing it to my OM352a 1988 engine which is very similar

Neil
 

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VerMonsterRV

Gotta Be Nuts
I also want to add that the smoke is only when it is cold out (say close to freezing). From what I have seen online I think this is normal for these trucks? As far as I have been able to figure out these trucks do not have what I would say is a typical American coolant tank with the hot/cold markings. All I see is a flat black tank with 2 caps above the radiator. No way to see externally the level, just got to open it a look in. From what I gather from the German owners manual we are supposed to fill it to the top of the opening. We are heading to El Paso today to meet up with the new rear leaf springs hopefully I will be able to get this fixed also while there.
 

Neil

Observer
Jon, sorry not coolant related but can you take loads of before after and during photos of the spring change over.

I am very interested in this conversion

Thanks from a sweaty Rio DJ

Neil
 
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