How I connected my radiator

Last update: 8/7/08

Return to home page links

Several people have asked me questions about my radiator connections, how I get rid of air in the system, do I have to remove the nose cone to fill the radiator, does the engine run hot with a small car radiator etc.

This article gives the details of how I plumbed the cooling system for my GSXR-1000 engine etc.

Suzuki GSXR engine coolant connections

My GSXR engine is a typical water cooled engine and has the same cooling elements as a normal car engine.

There is an air/coolant bypass hose connection at the thermostat housing. This connection is made on the engine side of the thermostat. The thermostat has the usual small air bleeder hole in it but the bypass hose is also used to fully vent  air out of the engine and afterwards to bypass some of the coolant as the engine is warming up. I will call it the "air bleed" hose from now on.

As in most liquid cooled engines, there is also another  water bypass hose connection on the engine. This hose allows a restricted amount of water to flow through the engine when it is running. This insures that the engine doesn't have large temperature variations as the engine is warming up before the thermostat opens. Originally this hose was connected to the inlet side of the water pump to continually circulate a small amount of water through the engine.

Both of these hoses are ~1/4" inside diameter and are under full radiator pressure. There are also the normal large inlet and outlet hoses that go between the engine and the radiator.

Other water cooled motorcycle engines will probably have similar connections.

My engine has a dry sump lubrication system which caused a unique situation as far as the water pump goes. Like most liquid cooled motorcycle engines, the GSXR uses a water pump that was attached externally to the side of the engine. My particular dry sump system replaced the water pump with the oil scavage pump. The water is now pumped by a magnetically coupled electric water pump that was supplied with the dry sump kit. The pump is surprisingly small but pumps way more water than a motorcycle engine needs. A similar sized pump on a jet ski can pump 360 gallons per hour.

Considerations for any cooling system
I consider the following things to be high on the list of things to do when you are laying out your cooling system.
1. You have to provide a method of venting air out of the engine and radiator.

2. All air bleeder hoses -have- to slope upwards to the final vent area (to allow the air to vent properly).

3. If you don't want to take your nose cone off to check/fill the radiator you need to provide a remote fill connection such as a remote (radiator) header tank. On a Locost the top of the radiator is typically lower than the highest liquid cooling area in the engine. This will cause air to be trapped in the engine. Don't feel bad, I had a XKE Jaguar that had the same problem!

4. The remote fill system has to be at the highest liquid point in the cooling system. With luck you can position the header tank so you can check/add coolant without removing the nose cone.

5. Don't forget to provide a drain valve connection at the lowest point in the cooling system.

6. Use anti-freeze that is proper for your engine since there are most likely going to be dissimilar metals in contact with the coolant. In my case, the radiator and header tank are copper, the engine is aluminum alloy etc.

Now we can get to the nitty-gritty of how I plumbed my car

Block diagram of my cooling system (obviously not to scale).

radiator dwg

Theory of how this setup vents the air
The main thing to notice in this diagram is that the air bleed hoses connect to the 1980s Triumph TR7 header tank at the highest point in the system. This insures that any air trapped in the system will work it's way into the tank and then be expelled into the overflow tank as the engine heats and cools off.

As you first fill the system with coolant, air in the system will be pushed through the air bleed hoses into the header tank and released into the atmosphere. Most likely there will still be air pockets in the engine block, radiator and even the main hoses.

When the system is closed up and the engine is run, the coolant and trapped air heats up and they will try to expand, which will build up radiator pressure. Water circulation will tend to push the air pockets to the highest point in the system, the TR7 radiator tank.

As the pressure builds in the system to the pressure cap release point, the air will be the first thing expelled into the overflow tank (which is always vented to the atmosphere).

When the engine cools down, the remaining volume of air and coolant in the system and header tank will contract which will cause a slight vacuum. This vacuum will draw coolant from the overflow tank back into the header tank. Over a period of time the system will become completely full of coolant right to the top of the header tank.

Notes and hints
There are many ways to connect up the air bleed, filler openings and header tanks.  The above diagram is the way I did mine.

Once all the air is purged from the system the small air vent hoses will be filled with coolant. The hose from the engine will then operate as a restricted water circulation hose as it was originally designed to be used. You will be able to feel that the small hoses heat up first as the engine is warming up.

The 3/4" diameter hose from the bottom of the header tank to the lower hose will allow you to fill the system quickly. Some header tanks are arranged so the upper hose goes -through- the tank. I've found that the header tanks tend to gurgle quite a bit and you have to take your time to fill the system. But either type of tank works fine once filled.

My son happened to have a copper Triumph TR-7 radiator header tank which he donated to the cause. The TR-7 tank allows you to fill the system quickly because the coolant enters the system through the lower 3/4" diameter hose. I  think filling the system via the lower radiator hose tends to flush more air out of the system than if the coolant entered the system from the top..

I needed a small hose connection on the bottom of the radiator to route the hot water bypass hose from the engine to the intake of the electric water pump. My radiator has a small copper tube tube in the lower tank that was intended to be used as an automatic transmission oil cooler. After eying it for quite awhile I decided to bite the bullet and convert it to the connection for the hot water bypass hose.

I plugged up the end of the tube furthest from the water pump with a short hose and an aluminum plug (held on with hose clamps). I then used a drill that just fit into the other end of the tube and drilled through the wall of the tube inside the radiator so the cooler tube is short circuited into the lower radiator tank. I then flushed out the chips with water and .....  wham bam Batman, instant small hose connection!

A car engine will probably have connections for the heater core. If you aren't using a heater, plug the heater hose connections. Do not connect a short piece of hose between the heater inlet and outlet hose connections on the engine. You will end up short circuiting the water flow and your engine will most likely overheat if you use an open hose that the water can circulate through.

If you have a rear engine car and are going to mount the radiator at the front of your car;
The long pipes you use to connect the radiator to the engine will also radiate heat so try to get some air flow around them. Even though it will be a little more expensive, I'd use aluminum or copper tubing for those pipes for maximum radiation affect. Also keep them separated so the hot pipe doesn't heat the cool water going back to the engine.

If possible, mount your radiator so the top of it leans forward in the nose cone. Once you install a shroud to semi-seal the radiator to the nose cone natural convection of heated air will tend to draw cool air through the radiator when you are not moving (IF you have a way for the hot air to escape once it goes through the radiator.) My air scoop is open around the top of the engine so hot air under the bonnet can escape through the opening.

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image".

Here is a picture of a mid-rear engined space frame car I built in 1965.


My 1962 Renault rear engine build used one upper and one lower frame rail as the radiator tubes. Naturally you have to make sure that they don't leak when you build the car. You have to run anti-freeze all the time so they don't rust out. If I had it to do over I'd just run two copper pipes to the radiator and make sure that air can flow around the pipes.  But the frame water tubes worked fine.

I used 1/2" and 3/4" electrical conduit for the space frame of the car. I gas welded the frame using coat hangers for welding rods! The body was made from two Renault Dauphine donor cars. The windshield and scuttle are the rear deck of one Renault and the rear of the car is the rear of the other Renault. The hood was made from one roof.

The radiator was sloped forward at an extreme angle and the hot air escaped under the car and between the back of the hood and the front edge of the scuttle. There was no fan on the radiator and the car never overheated (even with a supercharger I modified to fit the huge 850 cc engine). Considering that the car was made from two junked Renaults, it handled surprisingly well.
Return to top of page

Alright already, let's see how this system looks with real parts.

radiator rear view

My Honda Civic 1.5 L sized radiator is mounted to a sheet metal frame work that extends forward of the front chassis tubes. The sheet metal matches up to the four original radiator fan mounting holes. Four 1/4"-20 bolts hold the radiator to the sheet metal bracket. I've installed rubber bushings to the top mounting bolts (4 bolts are used to hold the radiator in place) for a little flexibility.  The electric water pump is at the bottom right of the radiator.

The closely spaced 1/4" bolts hold the original GSXR fan behind the radiator. The 4" diameter hose on the left bleeds some air from in front of the radiator to the oil cooler mounted in the aluminum box at the center bottom of the picture. The unpainted aluminum scraps around the top of the radiator are part of the radiator shroud. They hold the thick rubber shroud that contacts the nose cone.

The radiator cap shown in this picture has been disabled so it can't build up pressure. This is easily done by using a short piece of AWG #12 wire shaped into a "C" and slipping it under the small valve inside the radiator cap. You then crimp the wire slightly so it can't be removed.

This radiator cap is disabled so any air in the radiator will be immediately passed into the small gray air vent hose running off to the right of the picture. The small gray hose goes to the TR7 tank. The next picture shows where the small hose is connected to the TR7 tank. The larger hose is the hot water hose from the engine.

TR7 header tank

The TR7 radiator header tank (the red radiator pressure cap is on the tank) is mounted as high as I could get it without contacting the nose cone. The red cap on the TR7 tank is the actual pressure cap for the cooling system.

The TR7 tank and the plastic overflow bottle are mounted so the caps are just behind the rear of the nose cone and in the open when the bonnet ("hood") is removed.

The air vent hoses from the radiator and the engine meet at the "Y" adapter I made from some copper tube. There is a short hose that connects the "Y" to a small diameter metal tube that goes into and to the bottom of the  TR7 header tank. The TR7 tank is unmodified and has all the proper pipes etc since it was used in a similar manner on the Triumph car.

The gray hose is the air vent from the radiator. The shiny small dark hose from the "Y" goes to the air bleed on the GSXR engine. Both air vent hoses slope upwards to the TR7 tank. The connection from the "Y" to the header tank is the highest point in the cooling system.

The plastic bottle is the overflow tank. I have no idea what make vehicle it came from. A short hose connects the TR7 vent tube to the tube at the bottle that goes to the bottom of the bottle. The other hose is the bottle vent to the atmosphere and the open end is positioned to hang down below the engine. In use you add coolant to the overflow bottle as required.

The round aluminum tank is the 5 liter oil storage tank for the dry sump system.  Notice how tight the engine room is even with a motorcycle engine.

sensor fan

This picture shows how the 3/4" diameter hose that comes from the bottom of the TR7 tank (from the right of the picture) is connected to the lower radiator hose through two 3/4" "T"s.

The "T"s themselves are made from Home Depot 3/4" copper "T"s. They have a line of "T"s that are self soldering. The "T"s have a raised ridge around the outside of the "T" that is perfect for holding the rubber hoses on. I heated the copper and wiped the solder out with a rag.

The screw in sensor is a junk yard radiator fan switch. I machined the original threaded copper adapter down to fit into the left side of the "T" and soldered it into place. The switch is screwed into the adapter. Note the ground wire for the switch. The lower "T" was made from the same type of Home Despot "T".

All electrical connections to the cooling system must be grounded. This is to prevent any electrical leakage from eating away the metal parts of the coolant system (like your ENGINE or RADIATOR!!!). There are articles on the web about problems with ungrounded sensors etc eating up radiators, water pumps etc. It only takes a fraction of a volt to cause damage.

The TR7 header tank has what looks like a ground lug on it but it is really a floating electrical "water level" sensor. Do NOT connect anything to ungrounded electrical connections that are in contact with the cooling liquid.  Use anti-freeze that is in good condition since it is an electrical insulator.

How do you fill the system to eliminate as much air as possible?
1.  When first filling the system, I remove both radiator caps and fill the radiator itself until it is full.

2.  I then put the disabled pressure cap on the radiator and finish filling the system through the TR7 tank.

3.  I fill the overflow bottle between the "full" and "low" marks until the system stabilizes.

I don't have any trouble filling the system. It burps and gargles but it fills without trouble.

How to bleed the air out of the system a little quicker
I use a pressure cap with a lever to relieve the pressure. This is very handy to quickly vent air out of the system.

I allow the engine to reach operating temperature and then very slowly lift the lever. The first thing to be released into the overflow tank will be most of the air in the header tank. After the pressure equalizes, release the lever.

As the engine cools off, any air in the pressurized part of the system will start pulling a vacuum sooner than if you hadn't released the pressure and more liquid can be drawn into the header tank from the overflow tank.

I run the engine and release pressure cap lever a few more times after the first few drives.  After several heat and cooling cycles all of the air should be expelled from the system. You'll find that the header tank and the radiator will be completely full of coolant.  Do not remove the radiator cap without draining some of the coolant first or you will loose some coolant since it is not the highest point in the system.

Once the air has been expelled I fill the overflow tank to the "Max" line.

So is it worth all the trouble to do this?

In a word, YES!  

I can check or add coolant level by removing the bonnet and I have no problem with overheating even in the South Florida summer heat.

When I'm driving along the engine temperature runs right at the point where the engine thermostat starts to open (171 degrees F.). If I sit at a long stop light the temperature will go up to 190 degrees or so but cools right down to 171 degrees after driving a long block.

The fan has never come on in driving the car. Actually I wouldn't mind it if it would run a little warmer. I might not think that if I were racing the car though.  I've even put a resistor in series with the electric water pump to slow it down just a bit.  I do have a switch across the resistor so I can short it out to run the pump on full voltage if necessary.

Return to top of page

Return to home page links