[MR2] MK1 Coolant Problem

[Dennis McFayden]

I have found the source of this problem. The first thing I did to prove there was no leak during the cool down phase was to pressurize the system during cool down. The volume of coolant remained the same, no leaks. With this fact I decided that there was only one answer to the problem, an air bubble. In fact that is what I discovered after a complete bleeding of the system. 
 
My maintenance records show that this problem has probably existed since I last changed the coolant, a little less than one year ago. I also discovered that some air can remain in the system trapped in the pipe that goes between the plastic radiator cap fixture and the side of the car. This pipe should slope in a downward fashion. Mine was had a hump. 
 
I was very surprised to see how much air had been in the system. One way of checking this is to start with a full recovery tank. Use this fluid to keep filling the system as the air is removed. Mine went down about half. 
 
Remember to check the level of the coolant at the radiator cap when the system has cooled down. If the coolant is at the top then you have no trapped air. 
 
Dennis
--- On Sat, 9/19/09, Aaron Willis <te51levin at fastmail.fm> wrote:


From: Aaron Willis <te51levin at fastmail.fm>
Subject: Re: [MR2] MK1 Coolant Problem
To: "Dennis McFayden" <mr2garage at yahoo.com>, "MR2 Email" <mr2 at mr2.com>
Date: Saturday, September 19, 2009, 10:00 PM


Have you ever replaced the overflow cap and its hoses?  They tend to get
brittle and leak, if not come apart entirely.

On Sat, 19 Sep 2009 20:54:10 -0700 (PDT), "Dennis McFayden"
<mr2garage at yahoo.com> said:
> I posted this problem before and got a couple of good ideas but not
> worked. The problem is that my cooling system does not suck back the
> coolant from the overflow tank. 
>  
> I have replaced the radiator cap three times with new OEM caps. N o help
> there. The symptoms are:
>  
> 1) I have pressurized the system to 16 PSI for over an hour and the
> pressure holds, no leaks. I pressurized the whole system even the
> drop-down tube going into the overflow tank. 
>  
> 2) I have not lost any coolant. 
>  
> 3) With my pressure tester attached in place of the radiator cap I can
> create a vacuum to draw the coolant back into the system. 
>  
> The only thing I can come up with now is a possible flaw in the seal
> between the cap and the place where it attaches. No flaw is visible. My
> pressure tester attaches in the same way as the radiator cap. 
>  
> It may be possible(?) that air gets sucked into the cooling system
> instead of the coolant from the over-flow tank. That would be a rather
> complex one way leak that would not show up under pressure. I have also
> created a vacuum in the system to see if it would hold. It did but I
> didn't create much of a vacuum. 
>  
> Any ideas would be appreciated. The car cooling system doesn't come close
> to over heating, works very well even the the AC on and our high CA
> temps. 
>  
> Dennis
>  
> This is a '87 MR2 

-- 
Aaron Willis - '85 AW11 7A-GE, MSnS-Extra, E85, etc
Club discount on OEM Toyota parts - email me at work! awillis at lithia.com