Honda 1.8L running on test stand video

[redbaron]

Your engine is rated at 110 hp and has no time restriction ( 5 min on rotax ) the Rotax must drop to 80 hp after 5 min,s a big plus on climbout

[rv7charlie]

Charlie,

I know nothing about your engine, but some water cooled engines can be really tough to 'burp'. If you're boiling coolant, any chance you haven't cleared all the air from the engine itself? If the combustion chamber areas are getting minimal water flow, it will boil more readily.

If you're seeing a large temp drop across the rad, perhaps there's minimal water making it through the rad. That would allow the rad to drop the temp a lot more, especially if there's a significant pressure drop across the rad and the water is flashing to vapor in the rad.

On the subject of bypasses: again, don't know your engine. But the Mazda rotary I'm installing has as its stock thermostat a version opens a bypass when cold and plugs the bypass forcing flow through the rad as it heats up. Everyone I know about using the rotary plugs this bypass, and uses either a standard thermostat, or no thermostat at all for a/c use. *If* your engine uses this type of thermostat, and it's stuck in 'cold mode', minimal water might be flowing through the rad (see above).

Again, raw speculation. But guys flying rotaries have seen the issues I described.

Charlie

[BillL]

Originally Posted by rv7charlie

Everyone I know about using the rotary plugs this bypass, and uses either a standard thermostat, or no thermostat at all for a/c use.

The reason for a bypass closing thermostat is to maintain a constant flow velocity through the heads and around the cylinders regardless of the thermostat position. It can be critical for high load factor engines - aircraft engines operate at a high load factor. So, if it is really cold and the thermostat is nearly closed, then you would not want the coolant velocities reduced and creating hot spots in the head and at the cylinder at the top ring turnaround area. This thermal cycling is quite bad for head gaskets. Allowing the bypass to share the flow, or full flow if the thermostat is fully closed, (like on takeoff before it opens) is much less stressful on the engine.

An extreme case could allow the coolant to boil around the hot areas and cascade quickly to overpressure and belching of coolant even with a cold radiator. There must be flow.

[rv7charlie]

Bill,

No argument about theory, but most of the rotary guys don't run a thermostat, as I mentioned. (Lycs typically don't either, for the primary cooling path). The ones that do run a thermostat, don't start their takeoff run until the engine is up to temp (like we're *supposed* to do with Lycs). Sudden unbalanced heat load is one of the few things that can be really hard on a rotary (just like a Lyc).

No doubt the Mazda designers used it for precisely the reasons you state, because no one warms up their car before driving anymore.

I failed to state the reason the rotary guys do the mod. Most fear a stuck thermostat (either type can kill the engine if it sticks), so they plug the bypass & do full circulation all the time.

[rv6ejguy]

As Bill said, you must have flow inside the engine. Certainly don't plug the bypass if you run the thermostat. It will do exactly what Bill described here.

[charosenz]

Guys,

I really appreciate the comments and suggestions!

In addition to the main water outlet port from the head and the main inlet from the radiator that goes to the thermostat housing (that goes to the water pump, there are 4 other ports. Two are the inlet and outlet to the heater core. There are two more that provide water to the transmission cooler. It is worth noting that both of these returns enter the thermostat housing on the "hot" side of the thermostat. Hence both would be circulating water through the head independent of the thermostat being open - or not. I have one of the two bypasses open and functioning for exactly the reasons Bill has stated. I agree whole heartedly. Of course this is good and bad, in that they do provide hot water to circulate through the head as (they do not go through the radiator). This is good in that it helps the engine heat up fairly quickly. It is not good in that it provides hot water that is not circulated through the radiator - hence if the head is already getting water that is too high, this only makes the situation worse. I do have what would be the transmission bypass connected so it is circulating water as designed. I do not have the two lines that would typically go to the heater core connected. But it is important to know that this bypass is connected to the head exactly like the tramission bypass so it is functionally the same.


I do have suspicions about the air being trapped somewhere. I think the high delta is indicative of a water flow problem that goes way beyond the heatercore bypass lines not being connected.


I do have plans to lower the radiator and reverse the flow through the radiator. I have high hopes of getting this accomplished this weekend.

Here is a pic of the ports

http://www.halie.com/ov5.jpg

PS> I have ran with and without a thermostat and do not see any depreciable difference. Probably because once it heats up past the thermostat max opening temperature it becomes functionally irrelevant.


Thanks again.


Charlie

[charosenz]

Also just to comment a bit more about burping as RV7Charlie and others have mentioned. I have two ports the top of the engine that I keep open when filling the system. I also have clear lines coming out of these ports to feed the turbo cooling. I can see water flowing freely through these lines. Not to say this is a guarantee that there are no places where water could be trapped, but it is really hard to envision this. And honestly I think this may be my gremlin. Which is why I am going to reverse the flow and lower the radiator a bit more to try to eliminate this from happening.

We shall see....

Charlie

[rv6ejguy]

Trapped air is the #1 cause of cooling difficulties on auto engine installations. I've received many questions over the years and advised many folks on how to fix their problems. Hopefully you find the smoking gun on this one Charlie.

[charosenz]

Well, the saga continues. I moved the radiator lower and made sure everything was plumbed as smooth and as direct as possible to avoid any air pockets.

It seems better but it is still not cooling properly.

I found something fascinating in my testing. The delta (difference in temp between the hot side and cold side) of the radiator increases over 2500 rpm, and lowers when below 2500. To put this another way....below 2500 rpm the delta is about 20*F. The hot side is about 150*F and the cold side is about 130*f. At this point I am not running with a thermostat to increase the chances of any trapped air pockets to move fluidly up and out of the system. But when I increase RPM up to say 3000, the hot side goes up to 190*+F and the cold side goes down to as low as 115*F. Meaning to me the flow slows down, or may be worse, stops altogether. One of the two bypass systems from the head to the thermostat housing is fully open.


I painstakingly filled the system with coolant ever so slowly burping it all along the way. I have two 1/4" ports at the top of the head that exit to the turbo and I have a line off of the top of the outlet line that goes to the radiator overflow catch can to ensure that air pockets exit at the top.


To me.....it seems like the water pump becomes ineffective above 2500 rpm. Like cavitation. But I cannot imagine how air could be trapped there, and if so, what could possibly be done to remove it.....

But for the sake of trouble shooting, I am going to try to increase the size of the port at the top of the system so if it is trapped air, it will travel up and out. We shall see.

Feel free to comment, especially if you have any experience with water cooled engines....

I get some pics if anyone wants to look at them.....

Thanks!


Charlie

[rv7charlie]

To be sure we're on the same page, when you say bypass, do you mean from the water pump output back to somewhere on the block, without going through the radiator? If the answer is yes, is there any chance that when the pump starts working harder at higher rpm, more of the water is taking the path of less resistance, back through the block instead of through the rad?