RWD swaps & coolant flow (LX9)

[KLattig]

I've got an '06 LX9 (3500 from a Malibu) in an MGB, and have rotated the upper & lower intake manifolds to put the intake at the 'front' of the engine. I have a couple thousand miles on the swap, and it's running reasonably well.
I have 2 coolant temp sensors - one at the front of the head, and one at the back. I have noticed that the temp at the back of the engine oscillates from 180ish to 210F over a 3-5 minute period, while the front is reasonably steady at 195F. I'm baffled as to why the rear temp oscillates, but it's clear to me that the engine isn't being well cooled at the back.
Giving some thought to what happens with the rotated manifolds, I've concluded that the coolant is not forced to run the length of the engine - it is pumped into the left & right of the block, flows up to the heads, and out the t-stat housing - all at the front. In the original configuration, the coolant enters the block at the 'front', but the t-stat housing is at the 'back', so the coolant flows down the length of the block & heads before exiting.
Firstly, have any other 'swappers' noticed this? I've searched high & low, and no-one else seems particularly concerned (or has the instrumentation to notice the problem).
Second, I'm looking for feedback on a proposed solution: I'm thinking about drilling & tapping the rear coolant passageway in the lower intake manifold (1/2" NPT), then running the coolant forward to the heater intake pipe on the water pump. This would enable some coolant to flow completely through the engine, particularly when the t-stat is closed. The downside is that less coolant would be forced through the radiator when the t-stat was fully open. Also, I'm adding another possible failure point at the tapped opening in the LIM.
Any feedback or advice from prior experience would be appreciated!

[Guest]

Compare what you have to longitudinally mounted 60 degree V6s. You will see what you have is similar to what is laid out for them, and cooling is rarely an issue for them, except when there is a component failure or clogged system, just like it would be for any transversely mounted install.

The only thing I did differently in my longitudinal swap of my LX9 than other's do, is to add a coolant bypass from the block port above the oil filter to a bung I welded on the front cover inlet to the block above the port I had to weld closed to mimic the same potential. There is a potential other difference as well, and that is I removed the tube that runs under the upper intake manifold and moved the heater core return to the lower thermostat housing. I also used the hole that was left behind for the tube for my coolant sensor. The only change in flow here is that I no longer have the small restrictor plate behind the T-stat that would have been used for the original bypass.

If you ever have the heads off, you will see that when the gaskets are placed on the deck, that the holes at the front of the engine are for the most part blocked off, where as the holes at the rear of the engine are pretty open. This is to promote flow across the length of the head/engine block. Granted with the coolant exit at the opposite end of the engine from the inlet it forces the coolant to travel across the length as well, but I'm sure you'll find that after doing what you propose you will see little to no difference in the end.

I tried using the stock LX9 sender in the end of the head (front of the engine in my case) and saw large swings in temp like you are describing with your rear sensor. How are you reading the front sensor? Did you use the LX9 PCM and use the output from it? AFAIK, the GM PCM puts a buffer on the temp reading for the gauge and will dampen the swing.

I've thought about trying to play with the coolant flow and one day I might, but for now, it works and has worked for me on a couple swaps now utilizing the gen3 top end. A previous swap was a mixture of 3 generations of 60 degree V6. No issues with cooling there either.

[Superdave]

I noticed the same thing in my 3500 Camaro, never was an issue though. If I remember right it would even out at higher RPM's.

[KLattig]

Thanks for your thoughts, Raven - good food for thought...
I have two identical sensors in the stock holes in the heads. The one in the front is being read by the engine controller (Megasquirt 2/extra), and has no signal damping at all. The rear is being read by the stock MGB dash gauge, which has a lot of electronic damping.
I don't believe there are any RWD cars using the LX9. I think the most recent examples of 60degree V6s in RWD applications are the camaro / firebird from the late '80s & early 90's. I'm not sure any observations about coolant flow & head gaskets made on these old engines would apply to the LX9. If I'm missing something more recent or more relevant, please clue me in! Unfortunately, no one seems to have head gaskets in stock here (Phx area), so I can't check one out in person. I've looked at pictures of head gaskets online, and all the holes seem to be the same size.
I'm not sure I understand the point of the coolant bypass you installed. What was your reasoning for installing it?

[KLattig]

Superdave, it's interesting that you've seen the temp swings as well. I'm thinking that this is probably happening to everyone, but few have observed it since they're only measuring coolant at the front of the engine.

It seems that a lot of people have done the swap without taking any corrective action to improve coolant flow, which indicates it's not a big problem. One could argue that most of these swaps never see 50k miles, so long term problems never crop up.

[Guest]

The reason I mention the older engines is the coolant flow is identical to those. In the block from the water pump, a majority pushed to the back of the engine other than what escapes through the small steam holes that are present around each cylinder and then flows back forward through the head to the thermostat housing. When the intake gets rotated on a gen3 (or gen2 for that matter) the coolant flow matches what was used in the longitudinally mounted engines.

The idea behind the bypass was to mimic what GM did. In the gen1 engines (Which is where my front cover came from), there is a hole in the one coolant passage that lines up with a hole in the gen1 block. I wanted to mimic this, since I was eliminating the gen3 equivalent that is made up of the coolant tree attached to the top of the water pump and uses that S shaped hose that then attaches to the tube that runs under the intake. Most people just rely on the heater core as a bypass and it seems to work. I wanted to take it one step farther.

I've only started looking at the MS code, but I believe there is some buffering or damping of the coolant signal, so that any short term change is ignored to use only trends to enable and disable parameters in the engine control scheme. I'll have a look at that part again, since I need to anyway for another project of mine.

[KLattig]

Well, a bit of disappointment today. I removed the manifolds, and discovered that the crossover in the back of the LIM isn't actually a crossover! The ports in the back of the heads are 'blind', and what appears to be a coolant crossover from the outside is actually just the back intake passage.
Sure wish I'd remembered this when I rotated the LIM in the first place! (or that someone on the forum who'd had their LIM off recently had reminded me!)
Anyway, with the manifolds off, it's pretty clear that there is very limited coolant circulation to the back cylinders when the manifolds have been rotated. It's probably just some turbulent flow (especially when the t-stat opens) that nudges the coolant around. Interestingly, I observed some deposits in the 'blind' ports - looks to me like steam is building up back there & solids are precipitating out. The flowing ports near the t-stat were nice & clean.
So, now I'm having some deep thought about what to do next...
- I could massage my firewall a bit (a lot, actually) to enable the t-stat to return to it's original location (while still keeping the UIM in the rotated position so the intake is at the front).
- It might be possible to put some 1/4" fittings into the blind ports in the LIM & get some positive flow - but probably not enough to make much difference.
- I could pull the heads & try to narrow the forward coolant passages between the block & the heads a little - that might promote some front-to-rear flow in the block, and rear-to-front flow in the heads, but maybe at the cost of less-efficient cooling overall. Seems like I've heard of SBC guys doing stuff like this, but not sure what they were trying to accomplish. But looking carefully at online pics of the heads, it looks like there are a lot of coolant passages between the block & heads.

Still hoping someone else has tackled this problem & has some ideas for me!

[Guest]

You're WAY over thinking this....

The majority of coolant flow is forced to the back of the engine because of the headgasket passage openings and location.

Refer to this picture:


The only thing I've considered and have decided that the effort does not match the pay off is to add a couple tubes to the blind holes at the back of the intake and run these up and into the thermostat housing like some older engine designs can benefit from, but their cooling systems were not designed as well. This may actually make head cooling worse, by allowing too much flow around the heads, and not through the heads as it is now.

This is not a problem, never has been and never will be. You need to swap the connections to the sending units and I'm confident you will see the "problem" of the temperature swing also switch ends. Like I said I observed the exact same temperature swing from the sensor mounted in the front of the engine.

Notice the large hole in the gasket at the right side of the picture (back of the engine)? That's where the majority of the coolant will flow from the block to the head. Yes there will be some flow through the smaller holes along the head length, but not nearly as much as will flow through that rear hole.

And for reference of the block:


In the above picture you can actually see the deposits from the coolant left where the hole that is at the end of the headgasket is. The block and head gasket have been designed in such a way that a majority the coolant flow will be directed to the back of the engine before flowing into the head, where it will flow back to the front when the intake is reversed on a gen3 or in stock form on a gen1.