Petrol/Gas B58 Overheat at Highway (Motorway) Speed

[samnt650]

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.

 

[anand]

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]

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.

 

[samnt650]

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.

Pls keep us posted of your situation...

 

[anand]

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]

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]

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.

 

[TahoeGren]

Is HT-12 equivalent to the BMW LC-18 coolant?

 

[Clark Kent]

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!

 

[TahoeGren]

Thank you @Clark Kent ! Good to know the Nissan L248 is equivalent. None of them are easy to find. I just bought some HT-12 online directly from Valvoline, but I’ll see if I can source one locally or maybe go to the BMW dealer in Reno.

I’ll spend some time tomorrow to find the leak.

 

[C-Mack]

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.

 

[Lord Ripon USA]

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.

 

[TahoeGren]

Still didn’t find a leak. After the 15 mile drive home from where I stopped last night it did lose another quarter gallon of coolant, but perhaps there was air in the system. I topped up the coolant, ran the bleeding routine, and took a drive around the neighborhood.

The only signs of coolant (now dried) are around the HT reservoir. I wonder if there is a hairline crack in the reservoir or perhaps the cap is bad.

There are no signs of coolant/milkshake under the small area under the valve cover that is visible through the open oil cap or the underside of the cap itself, and no coolant smell from the exhaust. I don’t have a code reader with me right now, but I didn’t notice any misfire. Engine is running smooth now and was also running smooth last night when it was overheating.

No leaks from the hoses that I can see even at full operating temp. @C-Mack , I do see what you mean by the hoses potentially rubbing something sharp. The upper hose is simply zip tied to the fan bracket . I circled the zip tie in the picture below. Hoses can move around quite a bit. Under the big hose there is a smaller hose I noticed (I pointed to it with a blue arrow) that is awfully close to a sharp hose clamp from another hose down there. That could potentially rub and cut a hole.

So it’s still a mystery where all that coolant went yesterday. I’ll keep monitoring and only take short trips until I figure out the issue and/or I get it to service.

 

[C-Mack]

Still didn’t find a leak. After the 15 mile drive home from where I stopped last night it did lose another quarter gallon of coolant, but perhaps there was air in the system. I topped up the coolant, ran the bleeding routine, and took a drive around the neighborhood.

The only signs of coolant (now dried) are around the HT reservoir. I wonder if there is a hairline crack in the reservoir or perhaps the cap is bad.

There are no signs of coolant/milkshake under the small area under the valve cover that is visible through the open oil cap or the underside of the cap itself, and no coolant smell from the exhaust. I don’t have a code reader with me right now, but I didn’t notice any misfire. Engine is running smooth now and was also running smooth last night when it was overheating.

No leaks from the hoses that I can see even at full operating temp. @C-Mack , I do see what you mean by the hoses potentially rubbing something sharp. The upper hose is simply zip tied to the fan bracket . I circled the zip tie in the picture below. Hoses can move around quite a bit. Under the big hose there is a smaller hose I noticed (I pointed to it with a blue arrow) that is awfully close to a sharp hose clamp from another hose down there. That could potentially rub and cut a hole.

View attachment 7878882

So it’s still a mystery where all that coolant went yesterday. I’ll keep monitoring and only take short trips until I figure out the issue and/or I get it to service.

Yup, I have the exact same zip tie holding the top main hoses in place. I believe that was either a port or dealer remediation to keep the main hoses from flopping around too much. If you crawl under the front of the vehicle and look up at the back of the radiator fan shroud toward the passenger side you’ll see a spaghetti junction of those 25mm coolant hoses crossing over each other. Plenty of spots in that rats nest of hoses to rub against each other and the shroud.

In fact, it was a connector on one of the smaller hoses leading down the back of the radiator that was leaking on mine that I had to adjust the spring clamp on. It wasn’t the connector that was leaking but the hose as it was clamped to the connector. Fiddly to get to but after adjusting it hasn’t leaked again. This was also the same spot where I installed the anti-abrasion wrap, as like you also noticed, the sharp ends of the spring clamps are very close to cutting into nearby hoses.

Okay, there is one other hose you’ll need to check while you are under there and is very tricky to see. If you look up around the catalytic converter near to where comes out of the turbo charger you see a long hose covered in silver heat protection material which follows the contour of the transmission tunnel. It’s supposed to be held in place by a black retaining clip poking out of the tunnel heat shielding. However, the clip can allow enough slack in the hose that it droops down and nearly touches the converter.

There is a very sharp piece of metal (like a knifes edge) which I believe is part of the sealing gasket between the converter and turbo which could literally cut through the foil covering and potentially into the hose itself. Check that area out and let us know if you see anything out of the ordinary. It might explain why you don’t see anything in the actual engine compartment leaking as it’s happening more underneath the car well toward the rear of the engine compartment.

Honestly, I think some of these hose issues should be part of a recall. If you’ve done nothing out of the ordinary to your vehicle and it is leaking measurable coolant it has to be a hose somewhere that has been compromised. It’s possible but unlikely to be anything with the engine itself especially if there are no signs coolant is mixing with the oil but certainly give it all a good once over. I’m more inclined to believe a hose has shifted due to vibration, retaining clip letting go or chafing.

 

[MrMike]

Check that your thermo fan is operational and that the plug is connected.