The elusive 224/3.7 MerCruiser banger

I’m interested in these engines.

 

I'd like to hear from those who have dealt well with thermostats for this engine. I made a housing and it worked well with the Allis Chalmers thermostat in it but it was big , heavy and ugly. I bought a BMW inline thermostat in its housing , nice and compact for about $27 but the thing would not bleed air out of my engine's head so it overheated after running 2 minutes.

So I'm back to making a housing , probably one with a high flow thermostat as I believe in having all the flow you can get.

It is tempting to run with no thermostat, but if the engine runs too cool it will not last long.

 

The 488 thermostat housing (it has the t'stat recess and matched the 1-1/4" nipple in the head) connected to a Chevy housing in the upper hose. (I used Cosworth Vega as also 1-1/4" but a straight 1-1/2" would be more universal)You need to slightly elongate the holes.

 

Couple ideas....

Black one or take the "billet" one and give it a quick sandblast to make it look cast and/or paint it your choice of color.

https://www.summitracing.com/parts/pgp-prp-6835
https://www.summitracing.com/parts/pgp-prp-6836

 

Your method sounds inexpensive and quite good.
The housing must be part of the heat exchanger....I gave that to the dealer to sell as he gave the engine to me.
Next time I will save the housing if it does not have to be removed with a hack saw. I was going to use two chevy water necks bolted together but there may not be enough room for the long side of the thermostat. Thanks for a great idea.

 

I was considering these before I bought the BMW one that would not bleed the air out of my block.
They do look nice and probably would work well . There were a few user complaints about them warping and leaking but then that is the reputation of thin aluminum parts. ( something I'm dealing with today on my waterpump). It still is a good suggestion.

I could make one from a 2" aluminum pipe coupling with reducing bushings to short 1.5" o.d. pipes.
there would need to be spacers to hold the thermostat in place between the bushings. For spacers, I could get away with cpvc pipe or even pvc. which does not have the temperature rating .. I once made a pvc pipe coolant sand filter for a Ford engine that was plugging its radiator with casting sand, in 5000 miles all the sand was gone. For some unknown reason it did not melt.

 

I was looking at the SBF 90 degree thermostat housing on my OT 5.0 Mustang last night and then looked at one online. It seems that you could cut a water port in the end of the cylinder head, very much like the stock port, and then drill and tap to apply the 90 degree elbow. On SBF intakes it mounts to a flat surface, housing the thermostat and providing a bypass port all within the elbow. There are other angles for this unit as well, if a 90 is not to your liking.

You just need a flat surface to attach it to on the end of the cylinder head. There are a number of ways to achieve that if it doesn't already exist. Most aluminum heads are very close to completely flat already. You could epoxy fill the engraving and smooth it for example. If executed well it would look as if it were designed to be that way.




And in this pic you can see the recess to house the thermostat

 

A simple solution would be to drill and tap the head to receive the sending unit used in a small block Ford. They are super cheap and very common. This one, for example, is only $4.50 and there are cheaper versions as well as more expensive versions.

 

Dennis G. The 302 Ford tstat housing fixes ALL your issues! Not only would it house the tstat but it has a port that could be used for the temp sender. If you don't need the small hose nipple just don't drill out the head.

 

Triumph motorcycles used a copper head gasket, are able to reused after annealing. I never had problems and had MANY (7) Triumph's!

 

Especially if these have room for the long end of a reversed thermostat, it would be an excellent solution the built in bypass is essential ( as I found out)
One would only have to bolt another housing onto it and have an inline enclosure

thanks tjm and big dog. I will check prices today.

 

I was able to screw a small sender into the block coolant drain on the exhaust side of the block.

 

As I'm going through an engine right now, I am reconsidering coolant flow from the Toyota belt drive pump...it does look quite small . An electric pump would be far easier and BMW has used one on their X3,x5, 328i and 528i cars. I don't know its weight and flow rate . It is a 4 wire hook up and it costs less than the aftermarket electric pumps. 4 wires which Phil explains as relay connections in the next post

 

Here is something that may help you if you have overheating problems. A larger thermostat should flow more coolant A Motorad 302-180 is the largest thermostat in the store I go to. With some grinding, It will fit tightly into 4 inch fuel filler hose . I make end plugs of 1 inch aluminum plate and thread 4 inch lengths of one inch aluminum pipe into them for the hoses camp onto. Hose clamps hold it together and they are also used to squeeze the thermostat in place. It should resist galvanic corrosion as the aluminum is not in contact with other metal. If an internal sleeve is used to locate the thermostat, it should not contact the thermostat as stainless steel has a galvaninc potential difference with aluminum that should not be ignored. I'm still considering other materials for internal sleeves.

You often hear that the coolant should not move through the radiator quickly so it cools down more.
I think it does not matter as more coolant moves into the radiator to replace the cooled fluid and what matters is the amount of calories transferred. As a radiator transfers heat easier across a greater temperature difference, hotter water from faster coolant flow should get rid of more heat in the radiator.

1 calorie = the energy needed to warm one gram of water one degree centigrade.
1 calorie = the energy needed to warm 2 grams of water 1/2 degree centigrade

So if a small radiator is the limiting factor, faster water flow should work well because of the greater temperature difference between air and coolant.

 

Mysterious oil passage:
the area inside the valve cover has oil that leaks out of the engine from up there.
From that, I thought that drainage back into the sump may be restricted.

The problem is, the only drain I found is a 5/16" hole near the first valve lifter to drain to the sump from the head.
Big holes which seem to be oil drain holes are in the center of the head at the extreme front and rear of the head. Although there are matching holes in the gasket for the head's two drain holes There is no hole in the block that aligns with these two holes. I checked two blocks, they are identical in having one undrilled prospective oil drain passage at the block's front.

With head bolts and washers in place I see no way for oil to exit by flowing under them as it did in th Y block fords.
Is there a headbolt in an oversize hole acting as a drain?
I asked Mercruuiser tech help and they sent a diagram of oil raining down from the top of the engine. They did not know where it drained down.

I improvised an upward breather tube of 3/4" pipe that vented through a fuel pump block off plate. It did not make much difference there was very slight pressure from it, not even enough to inflate a balloon. I had another balloon on the valve cover vent and it also had only slight pressure. Both balloons pulsed indicating the existence of a functioning vent opening down to the crankcase.

the top of this engine lost a quart of oil that I collected in a pan after half an hour at 1000 rpm. There seems to be leakage under the valve cover gasket.

 

The 302 uses that nipple to feed hot coolant into the heater system or to bypass the t-stat if not plumbed to a heater. I believe the system requires a small amount of coolant to stay moving to remain functional until the t-stat opens and then most coolant then runs through the radiator.

 

Without a minor amount of coolant flow there would be no heat source to open the thermostat and cool the engine. My upper hose blew off with the inline BMW thermostat I tried. the engine overheated badly in 3 minutes at 2000 rpm under no load. I initially attributed it to the thermostat not letting air bleed through it for adequate coolant filling but even if the cooling system had filled there had to be coolant flow to heat the thermostat before the thermostat could open to allow cooling. Almost a "Catch 22 " situation.
This problem is a serious one for in-line thermostats. That may be why we see few of them.

 

an intake valve stem positive seal had come off {probably my fault}
So I replaced all of them. However, it made no difference in the heavy oil smoke that comes from opening the throttle briskly.
There had been external oil leaks but this was well solved with 3M black weather strip cement. I will use it in the future, sadly it is $11 a tube but it works very well. The lifter gallery cover is secured with flange headed bolts that squeeze down onto a o ring, I found that an electrical grommet works well here if you can not find a fat enough o ring..
A Kubota alternator is too tiny to keep up with my electric fan. Larger alternator needed.

 

has any of you run an oil cooler on a 3.7 merc? I have a 488 oil cooler somewhat like a big cucumber is it for cooling engine oil or is it for something else ?

 

You are quite right Dennis.
Its often been observed that running without a thermostat can, strangely enough, cause overheating. This puzzles a lot of people, and the theory that too much water flow through the radiator is bad, has become an urban myth.

The real reason is rather different, and a bit more complicated.
The water pump forces cold water into the block, the faster the water pump turns, the more water pressure the pump can create. If we place a deliberate flow restriction to water coming out of the cylinder head, we can GREATLY increase the water pressure within the block and cylinder head at high engine rpm. Pressure actually rises square law with rpm.

There may be a 14 Lb radiator cap (or whatever) to pressurize the whole cooling system, but when the engine is working hard at higher rpm, there can be 30 psi or 45psi water pressure inside the engine. That greatly increases the boiling point, especially around the combustion chambers and exhaust ports.

Solid high pressure water cools a lot better than a low pressure steam pocket, and everything works as it should, especially inside the cylinder head.

Now if you remove the thermostat, water just races around the system at 14 Psi, and it can actually start to boil around hot spots within the cylinder head, which can seriously reduce heat transfer into the water. The problem is not at the radiator, but inside the cylinder head. In fact its a very good way to crack a head.

If you look at a thermostat, the actual part that opens can be rather small, its much smaller than the water flow area everywhere else, and that is done for a reason.
Even when wide open, the thermostat offers a deliberate restriction to flow to allow pressure buildup that is needed within the engine.

If it does flash boil within the cylinder head, this will instantly drive up total system pressure and lift the radiator cap, you lose water, and it boils more. The problem is not water going too fast through the radiator ! But lack of water pressure inside the engine.

If you must run without a thermostat, fit a big washer in its place with a suitably sized hole (maybe one inch ?) and that should fix any boiling problems, assuming everything else is working properly.

I don't know if its of any help, but the Mazda Miata has an extended thermostat housing with a barbed fitting for the heater.

 

Very interesting read. Makes sense. How did you come to know this? You a cooling engineer or a race car engine builder or something like that?

 

It was something I read a very long time ago written by one of the all time engine building greats Smokey Yunick. A very clever man indeed !!

 

Ahhh...... well I've never read that but it makes a lot of sense. Thanks for sharing.

 

Above there has been conversation about using the SBF thermostat housing mounted on the front of the block. I must be messed up here. The hole on the front of the block at the water pump is the inlet, is it not? Isn't the discharge the 2 ports on the end of the intake?

I still have not ran my motor. Mine is a competition engine. My cooling plan is to run the electric water pump used as an intercooler pump on the Ford Lightening. This will be plumbed into the hole where the original water pump fed. The outlets on the intake manifold surface will T together feeding back to the radiator. I have the rear of the head drilled and tapped for a water temp sensor. I am going to use a Holley EFI system. That system has the capability to turn the pump on and off, OR it has the ability to control the pump speed using PWM . The pump will require a PWM driver to run it, which was available on some Ford or Corvette electric fan controllers.

Warpspeed has brought up some good water pressure information which I was not familiar with. It makes sense. I won't have that kind of water pressure. Now I'm wondering??

 

Those little Nippondenso alternators are available up to 60 or 65 amp (advertised). Most are 30 to 35 amp.

But that is a good point. I plan to run one.

 

I wanted to share the exhaust side of my motor. Unfortunately I think I have created an engine that will want to turn high RPM with the big intake, cam, head, and exhaust. What I need is torque at a quite lower RPM.

That is a 4" collector and tube. The long tube is needed to keep the O2 sensor happy. Holly recommends 24" minimum collector length after the sensor. My tuner wants 10 times the tube diameter. My length is between them.

 

Beck,
I see that you have a transmission in place. What is it?
How is your diet going? Can you make weight? What rear end did you wind up with? Glad to see you back

 

Inlet is on the back of the intake, outlet at head

 

Thanks you made it all clear. Thanks for the excellent helpful post on pressurizing the head.
I've been distracted by the huge nearby fires it is like Pompeii was.