Overheating E34 M5 S38 3.8 L

[Klippa]

I have an E34 M5 S38 3.8 L engine. Recently swapped engines, which is the 3.5L to the 3.8 L. Am now Getting temperature spikes and the radiator hose extremely pressurized (hoses rigid & tough) and has overheated at least once. No oil mixture in cooling system or the engine. Thermostat, Water pump, hoses new. Heater core is disconnected. Any suggestions?. Thanks.

[cirrusblau]

Maybe the head gasket failed with the combustion pressure coming over to the cooling passage that's why no signs of oil and coolant mixture? I assume you've bled the system correctly?

[Klippa]

Thanks....we are still bleeding the system...getting the air out.

[E34 Lives]

Check if thermostat is working and installed correctly with bleed hole on thermostat facing up, you can also try installing without thermostat temporarily to see if it resolves overheating.

There is a head gasket testing kit that test radiator fluid to see if combustion gasses have entered cooling system, very easy and accurate test to admisister.

[GazM3]

Yes just do the test of death. If it is getting hot it will pressurise greater and the cap is 2 bar for memory which will find weak points with the hoses and connections. Perhaps as a thought if there is no issue with combustion gasses in coolant, thermostat operation or the water pump, look at the waterless coolant from Evans. We cant get it here in Australia any more but it will run at much less pressure