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Petrol/Gas B58 Overheat at Highway (Motorway) Speed

samnt650

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Well damn, I guess I have the second case now. Very similar experience to you. Been off roading a handful of times, no overheating issues. Always try to wash all the mud off as well as I can afterwards. Then driving back home at highway speeds engine starts overheating. Light goes away the second I slow down or get off the gas. Turning the cabin heat on full blast seems to somewhat mitigate the issue. I contacted my dealer about it have not heard back from them.
When you have your truck at the shop, make sure they will test the vehicle at speed. Often dealer only do an idle test, or pressure test check for leaks. Also take pic or video showing the vehicle overheat only at speed. BTW, when did you take delivery? I got my on 12/28/23. Maybe your dealer should contact RDS (Philly) when they receive the truck.
 
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anand

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Yes all that is clean. But does someone know which is the main coolant reservoir and which is the auxiliary ? And if both reservoirs take the same color coolant?

Looks like blue cap reservoir is on passenger side and drivers side is black cap.

that
Main is blue, aux is black; both use the same coolant
 

j3t3r

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When you have your truck at the shop, make sure they will test the vehicle at speed. Often dealer only do an idle test, or pressure test check for leaks. Also take pic or video showing the vehicle overheat only at speed. BTW, when did you take delivery? I got my on 12/28/23. Maybe your dealer should contact RDS (Philly) when they receive the truck.
I took delivery end of February. I'm getting pressure test at my local mechanic, will then try to see if I can drive it to dealer 3 hours away.
 

anand

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I took delivery end of February. I'm getting pressure test at my local mechanic, will then try to see if I can drive it to dealer 3 hours away.
If it's overheating in any way, I wouldn't recommend driving it; historically speaking, inline 6 motors don't like to be run hot
 

255/85

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Main is blue, aux is black; both use the same coolant

Thought I should mention that, in US petrol models, the small auxiliary radiator in the lower right bumper - the one with the fan - runs off the main circuit (blue cap) and radiator. It's the one closest to the engine. In front of that is the auxiliary radiator (black cap) for the intercooler, etc. In front of that is what appears to be the transmission cooler. The lower left bumper has the transfer case cooler.
 

TahoeGren

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My Grenadier overheated today on I80 eastbound, just past Donner Summit. First sign was the heater blowing cold. I didn’t realize it at the time, thinking the system went wonky since I’ve read others here with random HVAC issues. A while later, I get the engine hot warning but had to continue on for another minute for safety reasons as there was no place to safely stop. This was in the middle of a snow storm and dark so visibility was quite poor.

Upon inspection, the coolant in the blue cap reservoir was empty! WTH I know it was full when I checked yesterday. Engine bay smelled like coolant, but I didn’t find a leak. The blue cap did have a bit of dry coolant splashes around it, I expect from the relief valve. I filled it with almost a gallon and a half of drinking water (I didn’t carry any coolant or distilled), and engine temps are back to normal. I didn’t see any leak inside but I suspect something to do with the heater as this is the first time it was used. It did seem to work fine, until it didn’t. I was able to make it to the house just fine, but I left the heat off.

I’ll have to schedule a service visit for this. In the meantime I’ll buy the correct coolant and inspect things this weekend. I fear for the engine. Aluminum engines don’t do well after overheating.
 

Clark Kent

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Is HT-12 equivalent to the BMW LC-18 coolant?
Fingers crossed you caught this early enough to prevent any damage. Bit of a mystery where the coolant went tho 🤔. If it leaked out there should be physical evidence. If it was burned through one or more cylinders, i.e. a head gasket, then those spark plugs should be discoloured and heading towards fouling. A pressure test and a coolant contamination test of the oil will confirm. A problem for your dealer.

LC 18 is BMW's codification. Lifetime Coolant 18.
HT-12 is the product ID.

Very good thread here including the BMW coolant part number. It's also listed in the @Rok_Dr's supplement.

Good luck! 🤞
 
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C-Mack

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I lay odds that it’ll be one of the many 1” (25mm) coolant lines that either chafed through (as the under hood routings are a bit suspect) or one of the many spring clips was not installed correctly and leaked. I brought home my brand new Fieldmaster and after a couple of days found coolant on the ground as one of the spring clips taking coolant to the front right radiatior in the bumper was leaking under pressure. I repositioned the spring clip to sit more square on the hose and barbed fitting it was going into and that stopped the leak.

Needless to say, I now watch all the coolant lines like a hawk as I don’t fully trust how the hoses are plumbed and can see many spots where they rub against each other or various other sharp objects under the hood. I even went as far as to put anti abrasion wrap around all the worrisome spots I could find.
 

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Pull the dipstick and look for mayonnaise.
Oh, wait…

Get the codes read and look for any misfiring.
Hopefully the exhaust tip doesn’t smell like coolant.

A long heavy pull at altitude is the test of tests for these vehicles.
Good luck identifying the issue.
 
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