Cooling Issues L28 Vintage Race Motor

[z-ya]

So I went back and looked at my notes for all the combinations I tried at the track last night. Before installing the return from the rear of the head to the thermostat housing, I had ran all combinations of thermostat, 1/2, 3/4, and 1" restictors. This was with the sensor blocking the rear coolant outlet from the head. I had only tested with the rear outlet hose installed and a thermostat (with 1/4" hole punched in it).

 

So last night I tried the 1" restrictor (same size as thermostat when open) in place of the thermostat, and ran the engine at 2000RPM until it got up to temperature. With a window fan on the radiator, and the ambient temp around 90F, the temperature at the rear of the head never got over 185F. So it looks like with the thermostat in there, it blocks the flow from the rear of the head enough that it gets much hotter than the rest of the engine. The coolant from the rear of the head mixes with the rest of the coolant coming from the front of the head keeping the overall coolant temp low enough that by the time the thermostat opened, the rear of the head was already at 230F. I have a feeling that if I was measuring coolant temp in the thermostat housing all along, it would have been well below 180F, and I would have never seen this overheating problem until maybe it was too late.

 

The next test and tune I will run the 1" restrictor and see what happens. On cool days I will just have to do the cardboard trick on the radiator to get the engine temps up.

 

I think the best place to monitor coolant temp is at the rear of the head. Monitoring it at the thermostat housing doesn't give you an indication of what the hottest part of the engine is doing.

 

I'll post results after the 7/7 test day.

 

Thanks,

 

Pete

[Tony D]

It's not my intention here to create an argument, Evans does have a 'patent' on this.

It is the first time I have seen it in person. Please reference the 'obscure second method' I mentioned earlier.

This was revealed to my by a GMI Engineer from SBC Testing in the last portion of the 1950's.

 

Evans is suing GM because they 'stole' his patented idea for reverse flow cooling on the new small block. As High School Students we were directed by that same GMI Engineer into doing a Trans Am 6.6 Liter Reverse-Flow Cooling system in 1979.

 

It's been revealed to me that (not in reverse flow configuration) Electramotive also used the Amot Bypass Controller in the early 80's as shown in the Evan's Patent.

 

Patents sometimes can be the purview of those who simply documented their work and not the original creators. GM knew about this for about 30 years before someone else patented it. Why they didn't who knows...

 

But that system has been known to people for quite a while. Before it was patented!

[Tony D]

"I think the best place to monitor coolant temp is at the rear of the head. Monitoring it at the thermostat housing doesn't give you an indication of what the hottest part of the engine is doing."

Put that as a sticky at the Cooling FAQ Threads!

[didier]

Hmmm. The patent there lays out some real good info.

 

Been reading up a lil bit on the head cooling threads, i think didier has this in the works for his setup? I could see that translating well into an l-series, however, it seems to make more sense in my mind to vent the head on the manifold side, and feed into the opposing side.

No, there is no place to feed water on this side.

But what diameter orifice would offer the best outlet for vapor, and not be a shunt for the coolant? Are there suitable areas on the opposite side to tap into

with reverse flow, just a little diameter is enough

Are those thermostats in that picture, pmc? Looks like they're staggered to fit the core plug holes?

With an electric water pump, i'll drive with megasquirt and pulse width, no need for a thermostat .

[Tony D]

Stagnant water is not good, one thing people forget about the stock pump, it generates 40 psig (around 3 bar) inside the block when running under load.

This increase in pressure assists in suppression of steam formation, when you remove a high flow pump and go with something slower, lower flow, even if in reverse, don't discount the loss of that pressure under load which formerly helped stop that formation.

 

Most electric pumps I've seen haven't produced flows comparable to the stock pumps and were only suitable for limited-applications.

 

They may fare better in reverse-flow due to increased efficiency, it is unknown until actual testing is done. It would be great to do an instrumented test run on an engine dyno where you can compare baselines before and after the cooling system modifications--especially the reverse-flow!

[didier]

Yes, i shall make tests with reverse and classic flow ,it is very easy to fix , and i know the EP will not produce 3 bars at maximum power, but there is advantage to get a constant flow without cavitation, and you can keep the pump running after shuting off the engine, it is a good thing for a progressive cooling down . ( right ?

 

Photos showing the water distribution holes in the head,above each exhaust port, and the big tube coming from the pump in the reverse system, or collecting in the normal flow direction .( who knows ?)

 

regards

Didier

260 Z 2+2 modified (just a little )

Edited June 25, 2012 by didier

[Tony D]

"but there is advantage to get a constant flow without cavitation"

Not really, the variable flow from the stock pump is due to variable heat input. More rpms, more BTU's into the heat rejection system.

IF the pump were capable of MAXIMUM EQUIVALENT flow rates, and you PWM trimmed it down I would say they had something there. But even with constant low flow, there is the possibility of cavitation. JeffP found the EWP was not up to it when pressed at higher HP for continuous use.

Remember, we had his engine on the engine dyno and were running 5 minute pulls at power to see if all temperatures were stable. With the EWP the coolant (even on the dyno) temperature kept climbing. When we went back to the Diesel pump, the temperature stopped doing that--indicating to us at least that the increased flow rate given by the stock water pump was justified.

These things usually work out in limited duration events, and on lower horsepower engines simply because the flow requirements are not that severe. When pressed, they seemed to fall short.

All that being said, it MAY be different on reverse flow, the efficiency gained by doing a proper cool to hot reverse flow of the heat source may decrease the flow requirement to within the range of the EWP to handle it. 5 Minutes at max power on an engine dyno will tell you.

Remember the photos on the cooling thread of Jeff's engine on there with the hose sucked closed???? Yeah, 5 minutes at 6300 and 450HP on CAST PISTONS and STEADY OIL/WATER temperature with the stock water pump (diesel)... Most guys don't run their engines for 30 seconds much less a minute at that level...but OEM's do. And you know Jeff, it's gotta be as good as an OEM or it's not good enough!

[didier]

Thanks for your knowledge, i'll keep it in my mind when the engine will start,

Didier

[Tony D]

Yes, we discussed this amongst ourselves---the reverse flow setup may allow for the lower flow of the EWP to function under full load. This would make both JeffP and I very happy (as others I'm sure!)

 

My experience with reverse flowing a 600HP 6.6 Pontiac back in the 70's was that the flow requirement was considerably reduced. I didn't know why then, but in subsequent education later in life I realized the flow path on an engine is exactly opposite of any proper heat exchanger! RARELY will there be anything BUT a counterflow arrangement (lowest temperature coolant coming into hottest part of exchanger first). For this reason, I believe the stock pumps have to be oversized, as well as sized to pump to higher pressures internally in the block to suppress the obvious issues with steam pocket formation and cavitation in the liners and heads which can occur from steam impingement.

 

We just ran out of time, and never got to the next experimental R&D session. As we were successful with stabilizing oil temperatures at or below 240F during these runs (WITHOUT EXTERNAL OIL COOLER) we were confident that the coolant system was adequate for the job, and wouldn't cause long-term problems. But being able to clean up the front end, and go electric for the possible post-cooling benefits still lurk in both our minds!

 

Keep us posted on your tests.

 

The oil jets, of course, would make another interesting thing to check on the dyno after knowing this engine had stable temps at 450HP under load after 5 minutes. Installing them on a known 'stable oil temperature' example would give a number that could quickly be calculated to determine what kind of BTU load these items produce.

 

It would almost be worth it (if there was the time) to do this to a bone-stock L28ET and run the tests! Like JeffP says "Every time you start talking, it costs me $2,000!" Curiosity killed the cat, but satisfaction brought him back!

[z-ya]

Still fighting cooling issues at high ambient temperatures on my road racer. I am really digging deep, and I think I am getting close.

 

For all tests I used a 3/4" resrictor in place of a thermostat

 

One test I have done was to check for air in the system by putting a section of clear tubing inline with the top radiator hose. Initially there was air bubbles, and some airation, but once the temp cam up a bit, and pressure built, there was no air in the water or airation happening. Tests were done at idle and up to 5000RPM. I also watched the lower hose and it stays firm for the entire test (no collapsing)

 

So it it is not an air, or pressure problem, then maybe it is a flow issue?

 

Here is my next test. I remove the top hose and put a hose on the thermostat housing (with a clear section to look for air) to divert the water away from the car. A shopvac hose works find for a discharge hose. Then I gravity feed the radiator inlet with a 25gal trash can. Then I ran the engine at 5000RPM and timed how long it too to empty the trash can.

 

It took just over a minute to pump almost the entire can (until it started sucking air). So let's say it's around 20GPM. During the test I did see airation in the water coming out of the engine. I'm not sure where that was coming from, maybe an air leak around a connection somewhere.

 

What I have been told by an expert is that 10GPH per 100HP is a good rule of thumb. My motor is 300HP. In 90F it can do almost 5 laps before the temp gets to 220F.

 

The pump is a diesel pump with a modified L6 timing cover. Anyone know what the flow rating of the stock L6 pump is?

 

Here is the test setup:

 

 

 

[z-ya]

I'm out of running ideas here, and the problem appears to be flow, so I am switching to a stock L28 Nissan OEM pump (cast impeller). I'm also swapping the timing cover for an unmodified L28E unit. If I have time to run the flow test again I will, but I have a time trial this weekend, and they are forcasting 85F for ambient temps, so I should know by next week.

[duragg]

Hi Z-Ya.

Where did you end up with your research?

Can you summarize some of your final lessons on this?

 

Tj

[Tony D]

I think your pump estimation was correct. The LD28 cooling water pump specs are in the Jesco Flyer in the Diwnloads Section.

[z-ya]

It looks like the problem was the head. Shaved 2mm, and 13.5:1 CR, it was leaking into the water jacket at high RPMs. Even a MLS gasket wouldn't seal it. I could see where the leakage was happening. There isn't much room between the coolant hol and the combustion chaMber on #5 in one area. We built another head last fall. we'll know for sure in a few weeks.

 

300HP can empty a trash can pretty darn fast!

[Tony D]

"Trash Can Full of Money" --- proper qualifier. We don't count water!

[Xnke]

Good one!

[z-ya]

Note that I didn't say what was in the trash can!

 

$3k later, we have a new head.....

[Tony D]

Been there...

[johnc]

On race engines I think in terms of dumpsters, not trash cans.

[duragg]

My track car cooled good this last event in Phoenix with new AzZCar radiator and front all ducted in to direct airflow.

Normal driving it is parked on the T-stat.

After 20 minutes of FULL flogging temp was 205 or so.

Traffic made it worse for sure.

 

In the middle of the night I thought it might be neat to hook up a coolant pressure gauge (from a spare oil pressure setup).

In event of a hose failure the pressure drop would be instant (along with the water on face)

Would the pressure also flail with head gasket and other issues?