Generator maintenace problem

[evrg266c]

Problem: Unable to completely drain coolant. We have a 7.5 Onan which has been recently serviced - we tried to drain the coolant to change but cannot get it to drain. We put radiator cleaner in to flush the system but now the generator will not start. Troubleshooting indicates a code of 3 flashes, pause, three quick blinks. This correlates to high coolant temperatures... What can we do to drain the system. It ran fine after service but then starts to run for a few minutes and quits.

[theoldwizard1]

Different but similar.

For DIYers, it is pretty much impossible to drain ALL of the coolant out of a modern truck/tow vehicle. The best you can do is remove the the lower radiator hose AT THE ENGINE which will likely give you a shower.

Here is the process I have come up with for front engine vehicles. Drain coolant capturing as much as you can for recycling. Add flush chemical (I use Prestone Flush+Cleaner; cheap at Walmart). If you have a large cooling system (rear heater), I use 2 bottles. Fill with water. Drive for 30 minutes with the heater on high. Drain and recycle.

Fill with fresh water. Drive 30 minutes. Drain. REPEAT ! The double rinse is important because you can never really get 100% of the old coolant or flush chemicals out. The second rinse will mean you have most of the residual fluid gone.

Fill with 100% anti-freeze, which ever kind is recommended my the vehicle manufacturer. (If you can not find anything specific on your vehicle, after the flushing chemicals and double rinse, you can use the old "green" coolant. It might not be the best, but it is better than letting the engine block freeze !). This is somewhat of a shot in the dark. Most trucks should Not need more than 2 gallons of antifreeze, because their total system volume is likely not over 4 gallons. So 2 gallons and fill with water.

Drive at least 30 minutes. Let vehicle sit until STONE COLD. Check coolant "strength". Check radiator level and overflow bottle. I top off with 50/50 mix.

[ron_dittmer]

I didn't realize the Onan 7500 had a cooling system with actual coolant. I learn something new all the time.

[Sam_Spade]

evrg266c wrote:
Problem: Unable to completely drain coolant.

This correlates to high coolant temperatures...

You have two separate and distinct problem here....probably.

You should be able to force water into the radiator until it comes out the drain clear.

Then if the sensor thinks that the coolant is too HOT when it really is COLD, then that sensor is damaged or disconnected. The chemical that you put in to "flush" might have damaged it. Let's hope for a loose wire.

[ksg5000]

Here's a pretty good Youtube video which shows how to change your coolant. Sounds like you may have missed a step or two and didn't purge the air from the system. https://www.youtube.com/watch?v=0LB5ZhvhXas


You must have a large Class C - most aren't diesels and they usually come with Onan 4k's - not 7.5. Regardless - video should help resolve your issue.

Good luck.