2.4DW in VW LT - Overheating on short runs - no load

[v8volvo]

Based on the diagram, I don't see any reason why that dashed hole in the upper radiator hose pathway (as it passes thru the ET) would need to be there. I think the purpose of that hole would be to burp air from the upper end of the radiator/engine connection, but there would be no need for it since the small hose that runs from the junction at (5) to the ET would serve the same purpose. So maybe that's why it is not present, as it'd be redundant.

This is actually a pretty nice design as shown in the diagram, with what appears to be better self-bleeding capability than the Volvo version has, since in this scheme any air trapped in the high point of either the engine or rad has a path to escape to the expansion tank. That's unfortunately not true for the Volvo installation, which is why we were talking about our special burping procedure that you won't have to deal with. I think we can be confident in this design that it should not have air in the system, since after running for any length of time it should have purged it on its own.

When the engine is running, do you see coolant flowing out of that hose that runs from (5) to the expansion tank? A lot or a little? And how large is that hose? Is it just a little (like 5mm) air purge hose, or a hose more like the size of a heater hose?

Congrats on getting it back running and doing the whole TB/WP job, that's pretty significant work and you made it sound easy. If you got that done without much sweat then I think you'll figure out this cooling issue soon. It can't be that complicated.

Let me sum up where I believe you are saying things stand at this point, so that we are all sure to be on the same page with our thinking:
- Water pump is new and engine timing is set correctly (both cam and IP)
- Thermostat is a new 87C from a good quality manufacturer, installed correctly (block-off disc facing inwards to the engine)
- The engine doesn't leak or appear to lose any coolant (right?). It gets hot when running, at least according to the gauge, but never over-pressurizes the system, blows coolant out of the pressure cap, has coolant mysteriously disappear and need to be topped off, makes air bubbles in the coolant or sooty/oily deposits, or any other indications of a leaking head gasket?
- As best we can tell, the cooling system is full, with no air pockets, and coolant seems to be circulating correctly (heater gets hot on both supply and return sides when the heater valve is open? Hot air blows from dashboard?)
- The only symptoms we see are that the temperature gauge reading is very high when running after a short time, yet hot coolant does not seem to be flowing through the radiator.

If all of the above is true, then as far as I can come up with right now, there are only two basic possibilities for what is going on:

Variant 1: The engine IS getting excessively hot as the gauge indicates, due to the fact that for some reason coolant is not flowing correctly through the system and is not being cooled in the radiator. The obvious first suspect for this situation would be a thermostat that is not opening, or is installed backwards, or a failed water pump, but we seem to have pretty much ruled all of those out.

The other possible reason for it, though, is that coolant is somehow finding a large volume bypass route around the radiator. I'm looking at the diagram and at your notes, and seeing that mention of a 4.5mm restrictor in the hose that runs from the upper rad passage into the expansion tank as an important possible piece of this puzzle. If that restrictor were not present, and if the hose is relatively large, then the result could be that hot coolant pumped out of the top of the engine mainly just recirculates through the expansion tank, thus taking volume away from what should pass thru the radiator core and achieving no cooling effect for the engine. How big are those orifice holes in the pass-through pipe for the lower rad hose? Big enough to move much coolant? Could that restrictor exist at the connection point to the ET, since it's not in the hose on your van? Is it definitely missing?

And in a similar thought process, is there anything else in the cooling system, like an aftermarket additional heater circuit or something, that could allow a large volume of coolant intended for flow to the rad to instead just loop around straight back to the WP inlet without being cooled at all?

Note that in this scenario, if there were any possibility for coolant to bypass the radiator, that possibility would be amplified if the radiator itself contained any restriction to flow. Remind us once more: you said you did take the rad out during a previous repair step and confirm that it didn't appear to have any buildup, restriction, flowed easily, etc, correct?

If we think that required 4.5mm restrictor may be missing, then one test (now that the cooling system seems to be purged of air) would be to gently crimp that bypass hose shut. Like with locking pliers with hose sections or tape over the jaws. That would halt flow through that circuit and determine whether it is affecting cooling capability.

Variant 2: The engine IS NOT getting excessively hot as the gauge indicates, and the overheat indication is due only to an electrical fault resulting in a skewed high reading. Based on what we have learned so far, this is the possibility I would want to pursue first.

Here's why: everything you have described is more or less is consistent with a correctly operating engine and cooling system, during the short distance/light load runs you have used it on. The heater hoses and core sound like they warm up with the engine, indicating correct coolant flow. The top of the rad gets warm, which usually occurs mainly from conduction even if the tstat is still closed, yet the lower hose stays cool. That, in itself, doesn't mean there is any problem -- to the contrary it could mean the radiator is in very good shape. If the load on the engine is light, the tstat will remain shut or only minimally open as the cooling demand is low. In that scenario, no or very little coolant flows through the rad, and what does is cooled down to near ambient temp if the radiator is flowing well and cooling efficiently. The only time you'll feel that lower hose get "hot" is if the radiator is nearing its maximum heat transfer capacity, which only occurs when the engine is working very hard in warm weather, and when the tstat is wide open for max flow. Even then, it should always be cooler than the upper hose, and under light load and temperate weather it can seem to stay cool the whole time. It's entirely possible that in the short distance, easy driving you have done on test runs, the engine just never works hard enough to really get the cooling system into action.

Put differently: from a certain perspective, you could argue that the only sign of trouble at all is what the gauge is saying, and everything else indicates a healthy system. If true, then that suggests the trouble is with the gauge.

ngoma earlier suggested using an IR thermometer to measure actual engine temps. That would be a great step now (if you can find one in the Covid era!), measuring at the heater hoses most importantly. You could also try an aftermarket temperature gauge, or just try replacing the gauge sending unit right off and see what that changes, since that's a quick step that doesn't require draining all coolant. I think there's a strong chance that once you get a secondary reading of temperature, it will show as being right on.

You have to be close now -- let us know what you find.

[blix99]

Thank you so much for such a comprehensive reply. You come to more or less the same conclusions as me, all though I'm much less qualified : ) I generally make everything up as i go along!!.

So, here goes:

Based on the diagram, I don't see any reason why that dashed hole in the upper radiator hose pathway (as it passes thru the ET) would need to be there. I think the purpose of that hole would be to burp air from the upper end of the radiator/engine connection, but there would be no need for it since the small hose that runs from the junction at (5) to the ET would serve the same purpose. So maybe that's why it is not present, as it'd be redundant.

This diagram is actually from a slightly later manual (1986) so maybe they changed the filling hole from the smaller by-pass section in the ET (as mine has) to the larger one which feeds the rad? However, this van is almost 40 years old so can't see that the current system has had it overheating for all these years

This is actually a pretty nice design as shown in the diagram, with what appears to be better self-bleeding capability than the Volvo version has, since in this scheme any air trapped in the high point of either the engine or rad has a path to escape to the expansion tank. That's unfortunately not true for the Volvo installation, which is why we were talking about our special burping procedure that you won't have to deal with. I think we can be confident in this design that it should not have air in the system, since after running for any length of time it should have purged it on its own.

As above, I'm sure this whole system has worked fine for years : )

When the engine is running, do you see coolant flowing out of that hose that runs from (5) to the expansion tank? A lot or a little? And how large is that hose? Is it just a little (like 5mm) air purge hose, or a hose more like the size of a heater hose?

The lower hose of 5 is pretty big but just runs straight though to the top of the rad. The smaller hose that tees of it has an external diameter of approx 30mm (just over an inch) I've just felt the joint where this tees off and there does seem to be something harder molded within, so probably the 4.5mm or similar restrictor is in place. As mentioned, this is a slightly newer diagram so 4.5mm might not be accurate. However, the smaller hose is near the top of the expansion tank and I guess is only really for excess coolant under pressure so nothing really comes out of it that i can see. I've also blown down this hose to make sure it's clear and it seemed OK.

Congrats on getting it back running and doing the whole TB/WP job, that's pretty significant work and you made it sound easy. If you got that done without much sweat then I think you'll figure out this cooling issue soon. It can't be that complicated.

Ha ha. I fumble along. I wouldn't say it was easy but it's just one 'small' job followed by another. By small I mean 'uncomplicated' eg: Removing the crank pulley was just a matter of working out how to lock the crank and undo a large bolt : ) Then next small job is working out how to get said pulley off. Then on to the next thing and on and on ...
I think this is why it's bothering me so much; it's not that complicated but I can't seem to fix it by doing the things that should seem to fix it : (

Let me sum up where I believe you are saying things stand at this point, so that we are all sure to be on the same page with our thinking:
- Water pump is new and engine timing is set correctly (both cam and IP) - yes
- Thermostat is a new 87C from a good quality manufacturer, installed correctly (block-off disc facing inwards to the engine)- yes- also re-tried the old tstat back in and tested both in a pan of hot water
- The engine doesn't leak or appear to lose any coolant (right?). It gets hot when running, at least according to the gauge, but never over-pressurizes the system, blows coolant out of the pressure cap, has coolant mysteriously disappear and need to be topped off, makes air bubbles in the coolant or sooty/oily deposits, or any other indications of a leaking head gasket? - no. no leaks and coolant stays clear with level constant
- As best we can tell, the cooling system is full, with no air pockets, and coolant seems to be circulating correctly (heater gets hot on both supply and return sides when the heater valve is open? Hot air blows from dashboard?)- yes
- The only symptoms we see are that the temperature gauge reading is very high when running after a short time, yet hot coolant does not seem to be flowing through the radiator.- yes

If all of the above is true, then as far as I can come up with right now, there are only two basic possibilities for what is going on:

Variant 1: The engine IS getting excessively hot as the gauge indicates, due to the fact that for some reason coolant is not flowing correctly through the system and is not being cooled in the radiator. The obvious first suspect for this situation would be a thermostat that is not opening, or is installed backwards, or a failed water pump, but we seem to have pretty much ruled all of those out.- yes

The other possible reason for it, though, is that coolant is somehow finding a large volume bypass route around the radiator. I'm looking at the diagram and at your notes, and seeing that mention of a 4.5mm restrictor in the hose that runs from the upper rad passage into the expansion tank as an important possible piece of this puzzle. If that restrictor were not present, and if the hose is relatively large, then the result could be that hot coolant pumped out of the top of the engine mainly just recirculates through the expansion tank, thus taking volume away from what should pass thru the radiator core and achieving no cooling effect for the engine. How big are those orifice holes in the pass-through pipe for the lower rad hose? Big enough to move much coolant? Could that restrictor exist at the connection point to the ET, since it's not in the hose on your van? Is it definitely missing?

And in a similar thought process, is there anything else in the cooling system, like an aftermarket additional heater circuit or something, that could allow a large volume of coolant intended for flow to the rad to instead just loop around straight back to the WP inlet without being cooled at all?

As far as I can tell, everything in this system is original and correct. I also think the '4.5mm' hose is doing what it should; which is just allowing any excess air or coolant to be purged into the top of the expansion tank under pressure and not for anything else.

Note that in this scenario, if there were any possibility for coolant to bypass the radiator, that possibility would be amplified if the radiator itself contained any restriction to flow. Remind us once more: you said you did take the rad out during a previous repair step and confirm that it didn't appear to have any buildup, restriction, flowed easily, etc, correct?

I have checked the rad when out of the vehicle with hot water from a kettle and the flow / heat seemed OK. However, I think I'm going to check it again in situ. I have to drain the cleaner from the system anyway so will fill the rad directly from the top with hot water and see if the feed hose to the tstat gets hot. I'll also see how quickly this happens.

If we think that required 4.5mm restrictor may be missing, then one test (now that the cooling system seems to be purged of air) would be to gently crimp that bypass hose shut. Like with locking pliers with hose sections or tape over the jaws. That would halt flow through that circuit and determine whether it is affecting cooling capability.

As mentioned, nothing seems to escape through this hose but it will eliminate it as a possibility so will give it a try.

Variant 2: The engine IS NOT getting excessively hot as the gauge indicates, and the overheat indication is due only to an electrical fault resulting in a skewed high reading. Based on what we have learned so far, this is the possibility I would want to pursue first.

I had considered this and might have already mentioned it earlier. This would indeed be ironic. However, I had intended to change the WP and timing belt and check timing, so this time wasn't wasted. Aslo the tstat was a good thing to change / check. It's the rest of the time that's been a PITA!!
Getting an IR thermometer is definitely the next obvious step to save my sanity. It's not unreasonable to think the gauge might just be reading high.
As you say, the only thing alerting me to the possibility of overheating is the gauge : )


edit: I've just borrowed a BBQ thermometer that has a range -50 deg C to +330 deg C so that will at least tell me the temp of the coolant in the expasion tank.

I will certainly report back.

Thanks very much again.

[ngoma]

Originally Posted by blix99

I had intended to change the WP and timing belt and check timing, so this time wasn't wasted.

That is important to keep in mind, great job you did there.

Some of us have a tendency to over complicate things. It can be quite a struggle to keep it simple. At this point, I see really only two main possibilities:

1. As stated earlier, the temp gauge is reading incorrectly. This is not as remote a possibility as is commonly believed. You can either substitute another sensor/wiring/gauge (many use a mechanical version as in many ways they can be more accurate), or you can take readings with a non-contact thermometer to give you a good idea of what is actually happening. I gave you some suggestions where you could take readings back in post #8.
DO THIS FIRST. It involves the least amount of work and time and --sorry to say-- should have been done much sooner.

2. Radiator is obstructed. You indicated you tested the flow but what was the volume? I don't know what actual GPM flow should be but seems like it should easily flow the output from a garden hose on full blast. Doesn't need to be hot water to test the flow. Don't put full water supply pressure to it at first, to avoid bursting it if it is indeed obstructed. (example: put the garden hose end in the radiator inlet and stuff it with a rag. Slowly open the spigot to full and verify full flow is exiting the radiator outlet.)

[blix99]

So, it's been a massive delay since i last posted but, this is because of lockdown and much work to do, I haven't had a chance to actually drive the van any great length.

However, I finally got to give it a proper run on it's 'maiden' camping trip - this 2.4DW engine is in a 1980s VW LT Karmann motorhome.

Anyway, just to recap - after much work trying to get the engine running properly after the previous owner had running issues and didn't drive it for four years prior to us getting it.

This involved a service, timing belts, a new injection pump end seal (it was drawing in air / leaking; the main running problem), timing the pump properly, new injectors and glow plugs, local fuel return hoses, fresh coolant and several new thermostats, it was still overheating, according to the dash gauge - the needle of which sat the overheating zone on the gauge and the red led flashed, even after half mile journeys and on cold days (5 to 10 degs C)

So, after checking (and rechecking) the rad, reservoir, coolant hoses, thermostat the last thing I finally did was change the dash gauge.

On our recent journey, the gauge sat between the middle led and the hot zone for about 30 mins then dropped to just above the middle led, I guess when the thermostat and rad cut in. This was in around 20 degs c outside temp.

So, problems seems to be solved and I'm happy. My blood is caked on the engine block, my sweat and tears evaporated : ) It's be a journey but thanks for all your help.

I appreciate everyone's input.

Thanks very much.

[ngoma]

What a relief!

I have mixed feelings over the fake overheating problem.

Feeling good you finally solved the problem.

Also feeling good we gave correct helpful info to solve this problem (in post #s 8, 13, 21, 23).

Feeling bad you had to suffer all that angst dealing with the fake overheating over the whole time.

Final score 2-1, put it in the win column. Hoping you get to enjoy your ride in the upcoming seasons.

[v8volvo]

Yes great to hear the successful outcome. Thanks for circling back to let us know how it turned out.

You really earned the good result with a lot of head scratching and stamina, blood and sweat. But got a lot of good work done along the way too, what with the timing belt service and cooling system refresh plus the injection pump overhaul. No question it will all pay off in reliability on your future travels with it. Cheers!

[blix99]

Thanks very much both of you.

I appreciate it. I recently bought an old side-valve motorbike that I can't get running now. I must enjoy this stuff in some deep recess of my brain.

I'm a glutton for punishment, I guess : )

Cheers

[barkster1971]

MEYLE 028 280 0001 THERMOSTAT COOLANT. Currently £9.16 on ebay . This is the 80 degree one.