Dumping coolant some time after switching off.

[jagwit]

Despite the fans cycling as they should, running on 82ºC thermostats, perfect radiator and temp being right in the middle of the gauge, my car would dump serious amounts of coolant every now and then. I could find no pattern to this phenomenon. When it dumps coolant, one can hear boiling noises from the engine.

My Jensen Interceptor did exactly the same. In the end, this was due to a hot spot that formed in the heads AFTER the engine was switched off. So, I suspected the E was doing something similar.

Having read about the "Lutz mod" on Jag-lovers, I decided to implement some version of that mod. With my die grinder, I ground the holes in the thermostat housing, tapered, just enough so I could fit a washer (with a 6mm hole) flush with the housing. This I did to both holes in the thermostat housing. The only washers I had large enough had 6mm holes. According to the Lutz mod (as for XJS) the hole nearest the front should be about 3mm but I now have them both at 6mm. I figured that more coolant would be flowing to the rear of the engine anyway. The gasket maker you see is simply to hold the washers in place until the housing is mounted to the engine where they will be trapped between the housing and the head.

tn_20170621_221745.jpg (173.48 KiB) Viewed 5322 times

Since I had removed the thermostat housing, I decided to check if the thermostats actually moved far enough to close the bypass port in the housings by boiling them up in the kettle. Sure enough, they both came up 3mm short. Fitted other thermostats that moved enough to close the bypass ports.

This meant that substantial amounts of coolant was simply bypassing the engine and whatever amounts did flow into the engine chose the path of minimum resistance and thus flowed right out the very first two ports of the head, leaving very little to flow to the rear of the engine.

I did an 800km trip this past weekend with these mods in place and I've had no more dumping of coolant. I also noticed the engine running cooler than before despite having to work hard on long uphills climbing from 900m to 1700m in altitude.

[SRK]

Interesting adding a fixed orifice to manage the recirc. Thats what we do in the oil industry. Have you put a temperature gun on the recirc line and then other place on the engine to see if the temps are close. That would likely tell you if you sized the orifice right.

Steve

[AussieEtype]

Hi Philip - your post highlights that generally the original design works and if it doesn't there is something wrong. And before making modifcations go looking for the problem and fix that.

When you replaced the thermostats with "proper" ones that should have fixed the problem, did you leave the modifcation you made? (as a precaution).

Living in a hot climate I have never had a problem with the cooling system or the old Opus ignition amp in the valley yet I hear of people living in colder climates having issues.

Glad you sorted the problem.

Garry

[MarekH]

To get the thermostats to seal off the bypass route, I fitted delrin inserts into the housings so that the foot of the thermostat didn't have to travel so far make the seal.

There are pictures on the old j-l site.
I'd guess that that alone would have done the trick.

One thing no one ever comments on is that whilst the Lutz concept may assist with circulation whilst running, it does nothing for you once the engine has stopped and is heat soaking. From looking at datalogs, what works post shutdown is to wait five minutes and then run the engine again fore no more than 45 seconds. This amount of time is just enough to take the volume of relatively cool water sitting in the radiator and swap it with the superheated (heat soaked) water inside the heads and block and drop the temperature in the heads down below working temperature. At this point, there is no further gain to be made by running the engine as the bypass will naturally shut off and redirect the now-too-cold water back into the engine. (The same concept can be applied to six cylinder cars which have the same problems.)

In principle, the "correct" size orifice is one which will always return water from the front and rear housings at the same temperature. Obviously that will vary with flow rate (rpm), load, etc, in real time.

kind regards
Marek

[jagwit]

I do acknowledge that fixing the bypass issue on the thermostats alone could have stopped the dumping problem as that alone would have resulted in more coolant passing by the rearmost cylinders. But why stop at a point that is "good enough"? Why not proceed to a point that is "even better"?

Have you put a temperature gun on the recirc line and then other place on the engine to see if the temps are close. That would likely tell you if you sized the orifice right.

Steve, I have such a gun and tried it but I was getting inconsistent and implausible readings. The metal finish of the object being measured plays a big role in the readings you get.

your post highlights that generally the original design works

Well, my DD6 is also indicates "that the original design works". "The design works" is not the end of the story. The real question is: "Does it work WELL?" I contend that the original design does not "work well". My XJS was also giving me similar issues in the beginning but somehow is not giving me this trouble any more - without the Lutz mods.

whilst the Lutz concept may assist with circulation whilst running, it does nothing for you once the engine has stopped and is heat soaking. From looking at datalogs, what works post shutdown is to wait five minutes and then run the engine again fore no more than 45 seconds

Marek, surely the point is that neither the original setup or the Lutz mod SHOULD HAVE TO DO anything after shutdown. If the engine has been uniformly cooled while operating there should be no need to run the engine again after 5 minutes.

I have cured the Jensen of its dumping problem by modifying the coolant flow through the engine during operation and all indications are that the E is now also cured of its dumping problem having modified coolant flow through this engine.