2H cooling puzzle/questions (1 Viewer)

[repentsinner]

Hi team Mud-

I've got a 2H that has been giving me cooling troubles lately. I'm not sure the issue is specific to a 2H yet, but thought I'd start here before asking more generally.

Some background: I rebuilt the head about 2000mi ago to fix some worn valves. Reassembled with new gaskets, everything torqued per FSM. I flushed and refilled the fluids, ran it around the city for a few weeks, and then did a ~1300mi trip with no problems.

Earlier this year I had to move houses so I put the vehicle in storage for a while, pulling it out in July to do a long weekend trip. On the outbound leg of that trip the engine overheated, with the stock gauge just touching the red. I stopped at an Autozone, cooled things off, topped up the coolant, and continued on my way. The engine stayed above operating temp but largely out of the red for the rest of the trip, although it kept needing to be topped up with coolant. On the way home, it started getting really hot any time we'd slow down - moving was fine but stopping at traffic lights would cause the temperature to rapidly increase.

From this behavior I assumed the cause was a bad fan clutch, but it still seems to spin fine. I've not worked up the balls to stick my hand in it yet, but I can't seem to get it to slow down like the youtube videos of bad fan clutches that don't take much of anything to cause them to stop spinning. If I turn it by hand with the engine off there's definitely the same amount of viscous resistance I always recall feeling.

I back-flushed the coolant system with a hose through the heater core until clear water was coming out everywhere. It doesn't seem like anything is blocked, but I'm not certain how to confirm that all passages are flowing.

Next I pulled and checked the thermostat. It opened fine in a pot of boiling water, but they're inexpensive to replace so I put a new one in. Running the vehicle with the thermostat out results in the coolant temp as being below operating temp as expected, unless it's really being pressed. Any time the new or old thermostat is in, the vehicle quickly overheats while operating under very low load.

While doing all of this, I noticed some bubbles at the radiator cap. I got a combustion gas tester, confirmed that it sees combustion gases at the tailpipe, and checked the radiator neck where I couldn't get it to register anything. There's definitely some sort of gas coming through the coolant system, but I can't tell if it's due to coolant boiling or a cracked head or head gasket leak. There's no sign of oil in the coolant or vice versa.

The coolant system is pressurizing well beyond what the radiator cap is rated to, causing the coolant reservoir to fill and overflow. After the engine cools, the coolant system never develops a vacuum to draw back from the reservoir - the system holds positive pressure more or less indefinitely after cooling. I assume this constant cycle of pushing coolant out generates a trapped air pocket that just gets worse, but any amount of topping things up doesn't seem to get rid of it.

The last thing I just checked was the water pump - I thought if it wasn't moving coolant effectively that'd explain the boiling over, as well as the significantly different behavior when the thermostat is in, as well as the inability to purge a trapped air pocket. I pulled the pump impeller and it seems clean - I replaced it a few years ago and it still looks effectively new. I don't really know how to check the specs of the water pump, all of the surfaces look like they're essentially where they should be, but I don't know how tight the tolerances are supposed to be.

I'm running out of things to diagnose here. The radiator is relatively new as well, and as far as I know there isn't a whole lot more to the 2H cooling system. Am I overlooking something obvious? Or do I have a cracked head or bad head gasket and it's just not pushing enough exhaust gas in to register in a hydrocarbon tester? I assume with a diesel, even a fairly small leak would cause the coolant to turn black like the oil does, but maybe it doesn't work like that. There was some sediment in the reservoir last time I drained it, should I try and get this tested somehow for hydrocarbons?

Thanks so much!

 

[coldtaco]

One of the things I would do is install a aftermarket water temp gauge. I did the same thing, but with a turbo. I had the water temp reach close to the top a few times on my drive home from Georgia to Alaska. After installing the aftermarket water temp gauge hot was just above the middle, like 245F if I remember correctly. I hate to guess what near or at red line would be. I had over heating issues and finally got it fixed with a new custom built radiator that I had extended another two inches on the bottom. Then last summer the coolant started to overflow while driving above 55mph. So today I finally pulled the head off to check where the problem is, but so far can't find any obvious problems, unless it is the pre-chamber cups (I think that is what they are called). I did the "smell" test and it showed exhaust in the coolant.

 

[repentsinner]

Thanks @coldtaco. Definitely not looking forward to pulling that head off again. Good to know that you had some success with a custom rad.

I put in new pre cups when I re-built the head - the old ones were cracked, but my understanding is that they all crack pretty much immediately anyway.

 

[roscoFJ73]

The coolant system is pressurizing well beyond what the radiator cap is rated to, causing the coolant reservoir to fill and overflow.

Its got to be something to do with compression gasses escaping into the coolant system.
Water pumps keep pumping till they stop

 

[wedgetail]

It could be as simple the fan hub needs a re oil. The over pressuring could easily be it boiling as it’s over heating. Some bubbles are always present due to the water pump.

It can be very tricky and inconclusive to try and diagnose a loose hub, much easier to just Change the oil. If you’ve never done it you should as part of routine maintenance anyway.

I’ve found in stock diesel cruisers 90% of overheating is radiators, 9% is fan hub and the final 1% other mechanical issues

 

[repentsinner]

@wedgetail thanks for the suggestion about the fan hub, I'll change the oil in it and see how that does. Any suggestions on diagnosing a bad radiator?

This cruiser does have an aftermarket turbo, but it's super low boost and has been on for a few years w/o issue.

 

[wedgetail]

Ah well that adds more probabilities in... 2Hs with turbos can (but not necessarily) have chronic over heating issues. Have you got a pyro?

Radiators can be blocked inside and out. You can sometimes see if they’re blocked on the outside - get someone to shine a torch in the fan side and see how blocked the fins are, can Be tricky with a ac condenser. You can’t effectively cleaned them in car you must pull them out.

They can also be blocked inside from scale. If it’s second hand or you haven’t been keeping up to date with the right coolant this is a Definite possibility. If there’s scale floating around in the system it’s a guarantee it’s blocking the rad too. Again it’s hard to tell, if it’s a swan neck rad especially, but see if you can look in to the core, maybe with a mirror. Rad shops used to service them by pulling the tanks and “rodding” them (pushing a thin rod through each tube), but most wont bother with a cruiser size rad they’ll just want to sell you a new one. But it could be acid bathed then flushed.

An infrared heat gun can be very useful to diagnose cooling issues. There’ll be a spec on top and bottom rad hose temp difference, unfortunately I don’t know the spec for a cruiser (I know for most cat earthmoving gear it’s 14*c at full operating temp and engine rpm). Too little and the outer fins are blocked, too wide and there’s an internal blockage

 

[roscoFJ73]

After the engine cools, the coolant system never develops a vacuum to draw back from the reservoir - the system holds positive pressure more or less indefinitely after cooling.

This is usually a symptom of compression gases escaping into the coolant. I had a vehicle once with a cracked head and it did exactly this. I would come out to the car in the morning and check the hoses and they would be rock hard after the car had sat overnight.
At first there was no milky gunk under the filler cap, but it began to form after few days.

 

[repentsinner]

Well it definitely seems like I've got a blown head gasket - I re-ran the combustion gases test on the gases being pushed out the rad and it turned from blue to yellow pretty quickly this time.

@Onur, you helped me source a 2H head gasket (11115-68020) last year, can you point me in the right direction to get another one? I can't DM you here for some reason

 

[repentsinner]

My reading of the old gasket is that there is a breach in the paper/fiber portion surrounding cylinder #2 to the small hole here (coolant port) as well as larger hole (head bolt). The bolt leak seemed to be mostly contained - although they're not explicitly sealed on top on a 2H, I guess it is snug enough to not leak out the top although the threads were pretty gummed up with cooked coolant.

I had the head checked for cracks and re-surfaced. There were some small cracks, but nothing that should have interfered with the gasket (e.g., inside edge of precup hole). There was a 0.004" warp in it which seems pretty minimal to me but I'm not a diesel mechanic.

I suspect that the gasket failed due to an initial overheat event caused by low/bad coolant (?), which then caused more overheating as the gases pushed even more coolant out? It seems difficult to deduce the actual initial cause here. Seeing how this failure works, I have a hard time understanding how the stop-leak additives work - presumably they'd have to fill whatever gap is formed at the metal part of the gasket?

Everything is back together now, and hopefully it stays that way. Although the FSM doesn't mentioning anything about hot torquing the head bolts, some of the other forums I've looked at suggested this. I got a little bit more out of maybe 4-5 bolts after bringing it up to temp. If I can stay motivated, I may check the torque again after 1000mi or so. It's too bad one of the rows is buried under the rocker assembly, as it requires two hot passes to check the bolts and then re-adjust the valve clearances.

The amount of gases in the coolant before and after the gasket replacement is night-and-day different. Previously it was continuously pushing gas out even when cold. Now I'm not able to detect any gases even after the thermostat opens and cycles through to the radiator.

Thanks everyone for weighing in! Appreciate the help with diagnosing this.

 

[repentsinner]

Some other notes for future Googling- apparently the OEM 2H head gasket is no longer available on its own, but as of late 2019 it is included as part of the engine rebuild gasket kit (04111-68022).

Also the water pump cover gasket (16129-68010) wasn't available when I went to order one, so I drew up a DXF and laser cut it from a sheet of fiber gasket from Napa. If anyone wants a copy of the DXF let me know - this is still a file type that can't be attached to mud. It might actually be in the engine rebuild gasket kit, I haven't sorted/identified all of the miscellaneous parts that came in that thing yet.