Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deacceleration"

[JustJason]

Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deacceleration"

tamd60b. Runs fine all day long. Rock steady between 180-190. Has a water pressure gauge in the seawater side. Sits at 15psi at 2800rpms all day long.

If you drop the throttle from 2800 to idle, gauge pegs to 30psi (again this is the seawater side). And coolant blows out of the overflow bottle.

If the opposite was happening, blowing coolant on acceleration, this would be an easy one. But it's just the opposite.
Acclerates fine with no apparent problems. Maintains WOT with no problems. It's just when you come off the throttle.
Any ideas?

 

[CharlieB]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Turbocharged motor w/freshwater cooling?

Intake pressure raises briefly when RPM suddenly drops due to turbo inertia.

Suspect a hairline crack in an intake port/passage, small enough there is hardly any coolant leaking into the intake, yet those moments when intake pressure exceeds coolant pressure it bleeds into coolant and causes puking.

 

[QC]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

I like it ^^^^ circulating water pressure would drop slightly under that condition, not sure boost would actually rise, but it would maintain for a second or two. Can you install a boost gauge and a freshwater side gauge to verify condition exists? Should only last for a few seconds though.

 

[JustJason]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

I like it to. The engine is not in front of me. I'm helping out a friend of my dads over the phone with it. I'm going to have him pull the intake and fill it up with acetone.
I'll let you guys know the outcome.
Thanks a bunch.

 

[Tail_Gunner]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

The motor more than probably has a air bubble or air is getting into the cooling system....similar to boiling. If the capacity of the system is two gallons and its full what possibly can create enough positive pressure to blow it out..Heat expansion almost every time

Back in the 70's this was a common occurence...you had to fill up the system wait for the motor to heat ...thermo open and watch it belch air and water until the system purged itself...ad water slowly to the system. If you just filled it up again quickly the thermo would close creating another bubble

 

[JustJason]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Tailgunner.
That would explain the coolant side of the system, but that doesn't explain the seawater side of the system, or the spike in the seawater pressure gauge.

 

[sasto]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Tailgunner.
That would explain the coolant side of the system, but that doesn't explain the seawater side of the system, or the spike in the seawater pressure gauge.

That seawater spike may be due to rapid deceleration. If your boat has mufflers, especially the lift type, you may have a problem with some back-up pressures in your raw water cooling exiting your exhaust.

Personally I throttle down from 2600rpm....gradually....trying to allow myself about 30 seconds to idle.....if possible.

I am curious as much as you on this one, JustJason.

 

[Brucetafer]

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

Re: Here's a weird one.. VP Diesel blowing coolant out of bottle on hard "deaccelerat

i know it means crap, but my aprilia motorcycle did the same crap, and i replaced almost everything in the world, to come to find out i had a bad cap on it and it was leaking air into the system... it would burp itself under extreme decel... blew up the system on turn 2 at laguna seca... that sucked.