[eeyang92]

Hey all,

I recently had my engine replaced with a used engine out of a non-LCI M2 (my car is an LCI) due to cracking a piston.

Everything seems fine, however once the car is fully warmed up and cruising on the highway, the coolant temp slowly approaches 100C, even in sport mode. I see the computer attempting to target 80C, and thus the fan and water pump are both running at near 100% capacity. To reiterate - this is just holding a 70 mph on the highway. As a consequence, oil temp also approaches 220F whereas it used to hold 195F before, which was right at the 2nd line on the oil temp in the cluster.

I know for a fact that the car was able to hold 80C coolant steady prior to the engine swap and I have datalogs from last year showing a steady 80C coolant temp when under light load. The log above was a 3rd gear pull - note how the coolant temps are just about 80C with oil slightly above that. After the pull, the coolant temp quickly returns to 80C.

So far I have swapped out the radiator (due to concern about a possible blockage), thermostat and water pump to remove any doubt that the failure might be in these components. I am running 50/50 water/coolant with water wetter. Situation remains the same - the coolant seems to be pegged to 100C all the time. This work was done by myself.

View post on imgur.com

Note about the image above - I captured after refilling at a gas station and starting to drive off - the oil temp dropped below 100C while the coolant remained at 100C, which leads me to believe this isn't a case of the oil running hot and pulling up the coolant temp along with it.

I know that the N55 thermostat fully opens at 100C, so perhaps this has something to do with this situation, but since the car was capable of holding 80C (and the ECU is trying it's best to do so by running the fan/water pump at 100%) I feel like this isn't related to the thermostat per se.

A few questions:

1) Is it possible that one or both of the oil and coolant sensors are faulty? I feel like this is unlikely since I have no codes and the values they report are consistent.

2) Is it possible there is a blockage in the coolant lines, near the engine? (Or even worse... in the engine block itself?) Is there a way to test for this?

3) Is there a second thermostat in the block itself that strictly opens at 100C? Is there some incompatibility between non-LCI and LCI engines? Note: I did instruct the shop that did the engine swap to use as many parts/accessories off of my original (damaged) engine, which includes the ECU. However, the entire small block is from the donor car.

4) Should there be shielding between the metal coolant hose and exhaust manifold? I see the clearance is very tight (1-2mm), which seems to me there might be a lot of heat from the manifold being put into the cooling system, but given the small gap, I doubt a heat shield would even fit there (and I don't recall seeing one before).

5) Is the fan and water pump running at 100% all the time is decidedly NOT normal? My fear is that this will cause premature failure of these components. When I turn the car off and the electric fan is running at 100%, it is extremely loud. I did not hear this loud fan noise prior to the engine swap.

I'm pretty much at my wits end trying to figure this out. I did verify the VIN for the engine is from an M2 via an online VIN decoder, and the engine model # on the block (N55B30A) seems to check out and match my old engine. (Note: A lot of online sources say that N55B30T0 should be the code, but sure enough, I looked at my old block and it was N55B30A)

Is there something I am missing here? Is the only action now to pretty much pull off all the hoses (and maybe even disassemble to block) to see if there are any blockages?

TIA!

[AmuroRay]

Were you running max cool mode before? And the oil thermostat is in the filter housing - that's entirely different from the coolant thermostat - which did you replace?

[eeyang92]

Originally Posted by AmuroRay

Were you running max cool mode before? And the oil thermostat is in the filter housing - that's entirely different from the coolant thermostat - which did you replace?

No, stock tune always kept the coolant at 80C. Max cool mode targets 70C. When I tried max cool mode recently, the coolant temp still would not drop below 100C.

I replaced the coolant thermostat (the one connected to the radiator).

[AmuroRay]

Honestly, try the temp sensor first. It doesn't make sense that the oil temp sensor or thermostat would have anything to do with it considering the oil takes long to come to operating temperature.

[eeyang92]

Originally Posted by AmuroRay

Honestly, try the temp sensor first. It doesn't make sense that the oil temp sensor or thermostat would have anything to do with it considering the oil takes long to come to operating temperature.

I will give it a try, although the coolant temp sensor (the one near the ping sensor under the intake?) does seem to be reporting values that make sense (i.e. when the car is cold, I see the temps rising as I drive, until it settles at 100C). It's just that it seems the system is unable to keep the coolant temp pegged to 80C.