Weird D24T Cooling system?

[volvo-dennis]

Hi Guys.

I have been looking through all the "coolant related" posts on this wonderful D24 forum. And i can't seem to find an answer to my strange D24-cooling problem. But i hope someone here, can help me out with my strange problem.

Here is the story: I live in Denmark (in scandinavia), and was on a 4000km road trip in my beloved 740 TD. Driving through austria, i suddenly see smoke/steam in the rearview mirror. The temp gauge was (of course!) in the middle = Everything is all-righty! But i pulled over in the emergency lane immediately, and found out the engine was missing about 5 Liters of coolant (1.3 gallon!). I added some water, and let the engine idle and cool a bit down.
I found out that the visco-bastard was not "engaging" correctly, so that was why the engine ran hot. Luckily for me, I had some tools i the trunk, so i unbolted the visco-fan, and "massaged" the little bimetal-thermal spring in the middle of the clutch. It was stuck, by the way… I continued my journey, and the D24 ran perfectly.. But the visco-fan was now fully engaged all the time.
When i got back home, the D24 suddenly had a strange habit to make the coolant disappear, sometimes. There were also air in the upper coolant hoses. The head was cracked, and the gasket were shot at cylinder 6.

And now to my strange problem: A used, but O.K cylinder head installed, with the correct MLS headgasket. My problem is that i can't seem to bleed the cooling system correctly.

While driving, the temp gauge is in the middle as it should. But if you park the car, with the engine running, then in 1-2 minutes does the temp gauge start to drop. bit, by bit by bit. And the idle-revs suddenly rises to 1000-1000 rpm, just like if the engine is cold. There is not really any pressure in the cooling system. The hoses are soft and squishy.
It idles in 30 mins, without getting hot or anything. It just runs high-idle all the time. If you take a drive after 30mins of idle, the gauge starts to rise again after a few hundred meters, and the idle drops to normal again. The outdoor-temp is about 50f degrees in these days.

- Engine runs perfect (timing is set, new timing belt + pump belt)
- The cab heater is working 100%, lot of heat!
- Rad is new (the big full-front type)
- Thermostat is new, but a cheap-o brand
- Visco fan still runs at full power
- Waterpump is ok (metal blade type)
- The little bleed-hose from rad top to reservoir is not bleeding coolant, unless the hose gets under rad-top level (?) If the hoses gets "squished", then coolant appears in the little bleed-hose.
- Upper rad hose is hot, and the thermostat housing is almost cool.. maybe about 70-75f.

Best regards

Dennis, from Denmark.

[RedArrow]

Hi Dennis,I`m not much help really, i know; but knowing `diesel volvo death-statistics`, i`d start with a perfect quality Thermostat like Wahler & a digital (infra red) temperature gun to see it better what`s going on exactly... and where...
Who knows the cond of that Tstat?
About air in the system you `can`t bleed`...: I`m sure you checked a million times for *any* possible leak too... any fluid loss!?!?? (radiator,rear coolant hose by firewall, clamps etc.
About pressure...: a retarded exp tank cap(??))


5liters is a lot. My story is: Once I lost more than a G of coolant due to a (not-tightened properly) expansion tank cap... system couldn`t get pressurized (thus being extremely ineffective)...was going strong,steady,loaded, in 3rd gear, m46 at 35-40mph, as part of a 30-40mile huge uphill highway around 3000meter elevation (togwotee pass), then suddenly hearing car burping up constantly like a vomiting baby then i saw my freaking gauge skyrocketing in a second, from center to all the way up but no steam, no drama (later I knew it was just Zerex g05 escaping quickly at the 75kpa cap. )
Obviously my heart stopped *before* i stopped the car itself... we both survived it.
Almost 2G of coolant lost&poured in, car kept burping for a while, I waited some, while calling my BeSt Volvo friend G As soon as gauge went back to normal I continued the trip with absolutely no issues relating to cooling system. Let me quote his words: `80C Wahler t-stat, part # 035 121 113, is the best one`.

PS.The gauge we have in there is an ignorant piece of junk, a lazy thing. A digital gauge is suggested best investment combined with a level sensor. Still haven`t done it, &%4#! If going crazy, you could wire up a small led test-light for you to indicate when fan starts. Drivers with ac,in traffic, will get annoyed by that.
I`m very curious what the big dieselers will suggest to solve your rpm issue.

Oh hey, nice job.Congrats driving home 1000+ kms with a sick HG. (wow) Welcome to the diesel forum!

[745 TurboGreasel]

One day my 6.2 tied the alt belt in a knot around the visco fan locking it solid. My only cue was climbing the mountain it was a little cooler than normal, and when I went down the other side, it cooled so much the glow plugs started cycling.

I bought a new $$OEM thermostat for my 740 that never opened, and I'd overheat past about 1/3 throttle. It didn't have the little hole you are supposed to install pointing up.

I second using the IR pyrometer to tell what is really happening.

[volvo-dennis]

Update:

I took your advice, and I have now changed the thermostat to an 80C, and the temperature gauge does not drop anymore, with the engine idling But I still have the strange rpm-problem. The cold-start do not lower the rpm's all the way down, when the engine is at normal operating temperature (starts at 1100 when cold, and stops dropping at 1000-950rpm).

But a now I have another problem with the darn' D24 I have now driven about 100 miles since the cylinderhead/headgasket change. And suddenly there is a little bit of engine oil in the coolant reservoir. I emptied and cleaned the expansion reservoir, and took a short drive. When took the rad cap off, i got disappointed. The coolant is covered with engine oil again. Isn't it always the oil cooler who is the culprit here?

[RedArrow]

Originally Posted by volvo-dennis

Update:

I took your advice, and I have now changed the thermostat to an 80C, and the temperature gauge does not drop anymore, with the engine idling But I still have the strange rpm-problem.
...
The coolant is covered with engine oil again. Isn't it always the oil cooler who is the culprit here?

Sadly, it did it again!? Better not driving it.
Wondering why it happened in such a short time/distance...
I`ve read it here a LOT that installing an MLS HG requires more attention than doing fiber ones; u Must* have Perfect* surfaces, etc & can`t just attack it the `regular` way (scratch).

[volvo-dennis]

Today i have flushed the cooling system with water, and bypassed the oil cooler. Afterwards i took a 15 mile test-drive. Sadly, the oil shows up again

It was not the oil cooler who was the culprit. Something must have gone wrong when i was putting the engine together. I do not think it's possible that it has been an error in the MLS gasket..

Now I will separate the head and engine block again, and check for errors.

Thanks alot for your answers so far. I will post an update again soon

[volvo-dennis]

Disassembly has begun...








The old cylinderhead. The prechambers (in US?) is leaning a bit. An old Volvo mechanic told me that this happens, if you often run a D24 at high rpm.


Engine block is being prepped' for new gasket.


The "new" cylinderhead.


MLS Gasket!






About to prep the new cylinderhead.




The old crack-head, about to be taken apart






The new head: It was a good thing I took the new head apart for valve-grinding. There were some soot on one of the valves.






Valves on their way out...


Hmm... inspection ongoing.

[volvo-dennis]

New valve stem seals fitted.


Ready to fit the cam, and valve adjustment.








The cylinderhead about to get a good cleanup.


MLS Gasket fitted!


Ready for manifold-fitting...






...Almost there!


After some miles, this happened...

...Story continues!

[745 TurboGreasel]

Ouch that sucks.
Pressure test the oil cooler, I haven't had great luck with them

Dishwasher machine powder (about a pint of it) run to operating temperature seems to do a good job of removing oil residue from the cooling system.

[volvo-dennis]

The oil cooler was not the culprit. It seems to be that there was something wrong with the MLS gasket I have now fitted an ordinary fibre gasket, and flushed the cooling system with some "Radiator Cleaner".

So far I have driven about 160km without any issues, so I really hope that it works now (knock-on-wood)…

/Dennis