Cooling System Plumbing: What am I doing wrong?

PradoTDI

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1997 Jetta TDI, 1991 Toyota LandCruiser LJ78 with ALH Swap
I have been daily driving my ALH swapped Toyota LJ78 for the past few months and the cooling system has been just fine, but recently I had to replace a couple of bypass caps, one of which is on the little nipple on the back of the cylinder head. I was informed that rather than being capped off that should be plumbed back into the cooling system to bleed off any trapped air in the cylinder head. I teed it into the return line from the heater core and oil cooler, and have since been experiencing erratic and high coolant temps, probably due to air trapped in the system.

I am not using the VW expansion tank because there wasn't a good place to mount it in the engine bay that was high enough up, so I am using an inline radiator cap and the factory Toyota expansion tank. My coolant temperature sensor is in the coolant outlet pipe coming off the back of the cylinder head. I disconnected the hose at the heater core valve and found it empty, but the radiator fill cap is full to the brim. I still get good heat from the heater core. When I first filled the system it bled out just fine.

My question is: is it necessary to have that small return line plumbed in, and if so how should I go about bleeding the air out of the system? I realized after I made all of the radiator piping that I have the inlet and outlet to the radiator switched, but until now I haven't had any issues with it. Are there any other glaring issues with my cooling system? I have attached a rough diagram of my cooling system and some photos.



 

CasaEd

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There looks to be a space next to the fuel filter where you could possibly mount a VW expansion tank. You should not cap off that pipe on the cylinder head because it is a bleed for trapped air and there is usually also a second air bleed in the hose that go's to the top radiator hose. I don't have a picture of the piece at hand unfortunately.
 

PradoTDI

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Thanks for the info. I realized the way I have the radiator hoses plumbed there are a couple of high spots that can trap air bubbles, and one of those spots is right where my temp sensor is located. I plan to redo the rad hoses to the correct orientation at some point, but don't have the time or space right now, so I'll do my best to get the air bled out of the system and see if that makes any difference.

I would love to be able to use the VW expansion tank, but the only places it fits in the engine bay put the fill level lower than the top outlet of the radiator. The space next to the fuel filter would put the tank right over the oil filter housing.
 

CasaEd

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From the pictures and the diagram you have drawn I cannot make out were the thermostat is plumbed into, it should be going into the bottom hose of the radiator, also the expansion tank you have fitted next to the radiator, is that original to the jeep ?
 

PradoTDI

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1997 Jetta TDI, 1991 Toyota LandCruiser LJ78 with ALH Swap
The thermostat outlet is plumbed into the top of the radiator. Toward the end of the swap I got a bit of tunnel vision and routed the radiator hoses where they fit best rather than where they should have gone 🤦‍♂️. I need to swap radiator hoses but don't have the time or space to do it right now. With the hoses going to the correct locations on the radiator I will only have one high spot that will be able to trap air, but should be able to make something like this to bleed off the air:

The expansion tank is original to the vehicle, it is hooked up to an inline radiator cap. Here is a better photo of the engine bay, the expansion tank is just visible in the lower right:
 

AndyBees

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I admit I hurriedly read thru this Thread.

Anyway this is my experience with the ALH and my swap into a VW Vanagon. Every "return hose" is important to coolant circulation. They should be connect/routed as close as possible to the OE set-up.

All the returns from the small hoses (non-radiator) should connect to the Black Steel Pipe that goes into the WP Housing (cast part of the block) just under the IP. The return coolant via that black steel pipe is what affects the functionality of the T-stat. If it comes back too cool, the T-stat will either never open or only open slightly. Example: The heater hose long run to the front and back on my Vanagon has a significantly lower coolant temp on the return when in use, which results in the engine temp running a bit higher than normal, even on cold days because that coolant keeps the T-stat, well cool and shut or barely opening.

As for the nipple on the back/end of the head, well, I have it plumbed to the expansion tank and a Tee-off to the out-going big hose to the Radiator via nipple as in one of the pics above in this Thread.

So, in my Vanagon, which has the engine in the rear with long hoses to the front mounted rad, I have never had any issues related to air traps, expelling air, etc. The Water Pump in these engines does and will move a lot of Coolant very fast.......... faster than you might think. Example: I have a Mechanical Pressure Gauge with pressure source tapped near the top of the Expansion Tank. When the pressure is near normal (7-9 lbs), when I accelerate (rev the engine), due to WP suction, I can see the Pressure drop as much as 5 PSI almost instantly for a coupe of seconds. That tells me the WP is robust with its purpose.

EDIT: Looking at the drawing again, I don't think your set-up provides enough coolant movement, especially with a heater valve shut-off. Otherwise, the only circulation is thru the oil cooler when the engine is bone cold. That's another reason to run a hose from the nipple on the head to the expansion tank. Also, on the Rad hoses, the Hot Coolant Hose coming off the end of the head should connect to the top of the Rad. The Return Hose from the Rad should connect to the black plastic T-stat Housing Flange.
 
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CasaEd

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That part you posted normally goes into the top hose, the small tube is then Tee'd into the pipe that comes from the back of the head and then joined to the top of the VW expansion bottle. If it were me I would ditch that original fuel filter assy, fit a mk2 golf filter closer towards the engine and then fit the VW expansion tank there.
 

jimbote

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So if I'm understanding your post correctly you have routed the hose from the thermostat housing to the upper part of the radiator? And the cylinder head outlet is going to the lower hose? If so, you absolutely must correct this! It's a fatal flaw and will cause an overheat situation. There's a very good reason the lower rad hose always goes to the water pump inlet (in this case, also the T-stat). In automotive applications, if the water level drops for any reason, the system will still pump coolant through the block and back to the upper part of the rad where gravity lets it fall to be picked up again by the pump. If you have those reversed, as soon as the level in the rad drops to below the bottom of the upper rad nipple, the pump stops pumping. I can 100% guarantee this is the cause of your problem. It's also possible that because you've starved the pump and t stat for water one or both may be damaged.
As for your question on the small nipple. It is for bleeding air and helpful to plumb it to the upper rad hose as high as you can get it in the system. You can also solder a nipple into the upper rad tank and plumb it to there.
 
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PradoTDI

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Thanks for the input, its very helpful in putting together a plan for redoing the cooling system. Unfortunately, I custom made metal piping for all the radiator hoses and currently don't have access to my fabrication tools, so I'm somewhat stuck with what I made for now. That said, I'm working on piecing together a temporary way to reroute the radiator hoses to the correct locations.

Interestingly, until I put in the little bleed hose from the back of the cylinder head, I had no cooling issues at all, even on a 6 hour highway drive.

So, here's my plan: stick one of these coming off the end of the inline rad cap, which will then go down to the metal pipe I made that comes from the flange on the cylinder head; that should take care of bleeding the air out of that hose and the little nipple.

Then, I'll need to find some radiator hose that has approximately the right bends in it to go from the thermostat outlet to the pipe I have going to the lower radiator port. That hose will still have a high spot that could trap air, right at the top of the thermostat outlet flange. Should I put in another bleeder for that one, or will it be ok?

As far as flow for to the thermostat when cold, the only difference in flow for my setup is that I have the line that would normally go to the EGR cooler blocked off. Is that an issue? If so, I could install a tee from the upper radiator hose just off the back of the cylinder head that would route down to where the coolant overflow return normally hooks in:
(Don't worry, it has a new plug on it!)
 

jmodge

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You are still referring to the thermostat housing as the outlet, it is the inlet, with the pump directly behind it. Air won’t get trapped in the lower hose because gravity is pushing coolant to the pump from the bottom of the radiator. Pumps need head pressure not to cavitate. So the outlet is at the top in the cylinder head. To prevent cavitation any air bleed goes to the top of the system. To dissipate heat, the coolant enters the top of the radiator and cools as it drops because heat rises. Air also rises above fluid, the reason for air bleeds enter high or they aerate the fluid. Hopefully this helps you understand the theory so you can think this through.
 

oilhammer

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There are just too many to list....
I'd like to add in that, in addition to the need for that bleed hose, you really should get the proper type tank in there. The truck has no "expansion" tank, it has an overflow tank. Which is not the same. Even modern Toyotas have a proper pressurized expansion tank.

The reason the old fashioned overflow tanks are bad, is that they allow certain parts of the coolant to evaporate away as a normal operation of the engine heat cycles. Which is why these older vehicles required periodic coolant checks and changes. Modern vehicles (and by modern, I mean Volkswagens all the way back into the '80s) don't do this. The only exception was the water cooled Vanagon, which in addition to the standard sized expansion tank also had an overflow tank. But this was mostly because of the sheer volume of the system made it difficult to deal with (and as anyone who knows Vanagons like I do, the waterboxer's cooling system was not without its issues anyway).

Another issue that people run into with this sort of swap is the heater. VAG (with rare exception) uses a constant flow of coolant through the heater core. Toyota doesn't. So when you switch your heater off in your truck (and some just close the valve when the temp knob is ALL the way to COLD), you block off that necessary flow. What is an easy fix for that, is a heater control valve that doesn't block the flow, but just sends it a different way. The H-shaped heater control valves like many Fords use work great for this. Because it allows that circuit to continue to flow like normal, but blocks it from going through the heater core. It just makes it take a U-turn at the firewall.
 
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jimbote

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I'd like to add in that, in addition to the need for that bleed hose, you really should get the proper type tank in there. The truck has no "expansion" tank, it has an overflow tank. Which is not the same. Even modern Toyotas have a proper pressurized expansion tank.

The reason the old fashioned overflow tanks are bad, is that they allow certain parts of the coolant to evaporate away as a normal operation of the engine heat cycles. Which is why these older vehicles required periodic coolant checks and changes. Modern vehicles (and by modern, I mean Volkswagens all the way back into the '80s) don't do this. The only exception was the water cooled Vanagon, which in addition to the standard sized expansion tank also had an overflow tank. But this was mostly because of the sheer volume of the system made it difficult to deal with (and as anyone who knows Vanagons like I do, the waterboxer's cooling system was not without its issues anyway).

Another issue that people run into with this sort of swap is the heater. VAG (with rare exception) uses a constant flow of coolant through the heater core. Toyota doesn't. So when you switch your heater off in your truck (and some just close the valve when the temp knob is ALL the way to COLD), you block off that necessary flow. What is an easy fix for that, is a heater control valve that doesn't block the flow, but just sends it a different way. The H-shaped heater control valves like many Fords use work great for this. Because it allows that circuit to continue to flow like normal, but blocks it from going through the heater core. It just makes it take a U-turn at the firewall.
On the ALH, heater control valves don't block flow from the rear outlet because the heater nipple shares a flange with the main return. As far as the coolant bottle on swaps i haven't used one for over ten years on my toyota. Rarely have to add coolant either, and quickly closing in on 200k miles 😃
 

AndyBees

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OP, in addition to what I said in Post #7 :cool: , these last three posts from Jmodge, Oilhammer and Jimbote have armed you with everything you need to clean-up the coolant plumbing on your conversion project.

Have a great day!
 

PradoTDI

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You are still referring to the thermostat housing as the outlet, it is the inlet, with the pump directly behind it. Air won’t get trapped in the lower hose because gravity is pushing coolant to the pump from the bottom of the radiator. Pumps need head pressure not to cavitate. So the outlet is at the top in the cylinder head. To prevent cavitation any air bleed goes to the top of the system. To dissipate heat, the coolant enters the top of the radiator and cools as it drops because heat rises. Air also rises above fluid, the reason for air bleeds enter high or they aerate the fluid. Hopefully this helps you understand the theory so you can think this through.
I guess I shouldn't be posting late at night :rolleyes: I get my terms all mixed up! That makes total sense, reading through your post makes me realize that I already knew all that in theory, but somehow didn't apply it here. Going to make a run for parts later today, hopefully the local stores will have enough stuff in stock that I'll be able to cobble something together to get me to the end of the month when I can rebuild the whole system.
 

jmodge

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I think The placement of the thermostat at the engine inlet throws peoples thought process off track, I have noticed some on the TDI swap page reverse their hoses and have cooling issues when they work the engine
 

AndyBees

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PradoTDI, when I did my conversion, I noticed in the Classifieds that several people had replaced all the hoses on their TDIS (MK4) and were offering the old hoses for free plus shipping. I grabbed a couple of those and used them to fabricate the cooling plumbing for the ALH engine swap in my Vanagon. Obviously, one end of those hoses was a perfect........... and, fortunately, the original steel plumbing on the Vanagon was basically the same fitment. So, a little deciphering and cutting, I came up with a good plumbing system with no issues except the slight hotter engine temps in winter when running the heater as I mentioned previously. Based on real-world gauges, the engine never goes about 202f under those circumstances.

Back in 2014, on the first day of a major 31 day 12k mile road trip, the mechanical coolant pressure gauge pipe come loose under the dash .............. long story short, I did the entire trip without the cooling system being pressurized with no issues period! I never had to add coolant, no high temps, etc., even though I was pulling a popup camper. Point is, if it is plumbed properly, the cooling system will work just fine!
 

PradoTDI

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So, I was finally able to round up the various bits and pieces to swap the inlet and outlet rad hoses. Here is the temporary solution I came up with:


After burping the system to get all the air bubbles out, I took it for a long test drive (~45 minutes at highway speed, 1hr slow off road, another 45 minutes on the highway). The ambient temperature was around 40ºF (4.5ºC). While the temperature is more under control than it used to be, it still seems to run hotter than I'd like. Temps seemed to settle out at around 200-207ºF (93-97ºC) on the highway. Before I changed anything at 32ºF (0ºC) ambient temperature the coolant stayed between 188-195ºF (87-91ºC) for hours on the highway, and after I added in the bleed hose to the heater hose I would get temperature spikes above 210ºF (99ºC) even on short drives. I did notice on my test drive that while the top of the radiator got hot, the bottom was always cool to the touch, as was the return hose to the thermostat. My radiator fan is programmed to turn on at 198ºF (92ºC) and off at 188ºF (87ºC).
So, is my temperature sensor placement giving me a higher reading than would normally be seen, or should I be looking for something else wrong with the system?

Just for kicks, here's the rig in question:
 

jmodge

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Does it make any difference if the heater valve is open or closed?
 

jmodge

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I don’t know if this is relevant, but on the car that small bleed hose off the head goes into a T and the third and goes up to the expansion tank. But anyway, It sounds like it is not circulating if the lower hose is cool. Does it ever warm up?
 

PradoTDI

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Does it make any difference if the heater valve is open or closed?
I did run with the heater valve closed a little bit of the time, but because it was chilly out (trying to snow) that got uncomfortable. I didn't notice any difference, but I may not have had it closed long enough. Hopefully it will be warm enough this weekend to do another test run with the heater closed.

I don’t know if this is relevant, but on the car that small bleed hose off the head goes into a T and the third and goes up to the expansion tank. But anyway, It sounds like it is not circulating if the lower hose is cool. Does it ever warm up?
I only checked the lower rad hose once, after about 30 minutes on the highway. It was cool to the touch apart from right at the plastic neck that goes to the thermostat, which was warm. So either coolant isn’t circulating past the thermostat properly, the thermostat isn’t opening like it should, or the radiator is amazingly efficient (doubtful). Looking at the ALH cooling system diagram, I think I may need another coolant line to circulate coolant to the thermostat, since I only have one circuit currently.
 

jimbote

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temps you describe are within normal range and the hot at top cool at bottom rad is normal. If you want lower coolant temps try a cooler t stat. I promise your t stat is opening and coolant is circulating. If it was not you would have already experienced old faithful syndrome. 210f is not hot in a properly functioning cooling system. In my Tacoma ALH swap i ran a "hot" t stat for over a year with temps @ or slightly above boiling (212+) with zero issues.
 
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jimbote

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The radiator is designed to efficiently scrub heat so there will always be reserve cooling capacity. If the lower rad ever gets as hot as the upper you're in trouble because all the reserve capacity to cool is gone and you'll soon experience an overheat if load conditions persist or increase.
 

PradoTDI

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temps you describe are within normal range and the hot at top cool at bottom rad is normal. If you want lower coolant temps try a cooler t stat. I promise your t stat is opening and coolant is circulating. If it was not you would have already experienced old faithful syndrome. 210f is not hot in a properly functioning cooling system. In my Tacoma ALH swap i ran a "hot" t stat for over a year with temps @ or slightly above boiling (212+) with zero issues.
Thats great to know, thanks! I guess I'm just used to the temp gauge acting like it's glued to the 190ºF mark in TDI's. If temps are a problem in the summer I'll look into a cooler thermostat.
 
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