When going with a Griffin or other race type radiator I strongly recommend the 2" core, not any big thick thing especially for slow running.
With the thick core the air passing through warms as it passes the front of the core and by the time it is going through the back half of the radiator it no longer cools anything.
The 2" core is more than generous for what you need.
This is my 3.8L Gen 2


And this is my turbo gen 1 twenty some odd years after building it.

Aluminum radiators transfer heat more efficiently than brass cores do. That's Griffin's reasoning behind how they build, and I've heard good things about them.

Another cause, and it's been brought up about the 3.5 DOHC's is that the water pump doesn't move a whole lot of volume. I wonder if the inlet vs. outlet temps on your present set-up is acceptable, but there just isn't enough coolant getting through. Just a thought.

John B.

Thanks for jogging my brain. I run a Howe in my 'Bird but it's been 20 years since that went in and I'd forgotten all about that.

Edward

No problem. A lot of people don't do this and end up hosing their cooling system. <img src="/forums/images/graemlins/kewl.gif" alt="" />

OldColt: I'll keep that in mind. The guy I spoke to at Griffin broadly suggested the 2 row (1.25" tube), 2.75" thick version based on what I told him. 5500 lb. GVW vehicle crawling in 100 degree temps and 70 MPH on the highway. It was just a guesstimate without actually seeing the factory radiator.

I actually decided to go with Griffin. I shipped off a factory radiator this morning - supposed to show up there on the 6th. Once they get that we'll have a call and discuss all the details. 5500-6800 lb. GVW truck crawling in 100-105 degree temps with the air conditioning on and 70-75 on the highway in the same temps.

BTW, I think that's the first time I've seen your turbo Gen1 setup. Nice!!!



John: Yea, I've been wondering that myself. Given the insane gearing my Sport has it's not unusual to pull long, very steep grades at less than 2000 RPM. I noticed today that at idle while parked, after sitting for a while in 95 degree weather the coolant temp was about 208. I revved up to 2K RPM and in less than 5 seconds the temp was down to 199 and then just stayed put until I shut it off 2-3 minutes latter. Sometimes it seems like I have enough air flow, just not enough coolant flowing through the radiator. <img src="/forums/images/graemlins/confused.gif" alt="" />

I was thinking about speeding up the water pump just a bit but I have no idea where to get a smaller pulley.

BTW, any links for the 3.5 DOHC discussions?

Edward

What about an auxiliary electric water pump from a mercedes or the like?

How would that actually work? If the aux water pump pumps more more volume than the stock pump it seems to me that the stock pump would block the extra flow. Doesn't the Mercedes have a bypass to make that work?


Update:

Ok. I burped the cooling system. Again. That helped with the cooling a bit. The gauge settled down a little, too, and so far no more P0125 codes. Dang. I keep forgetting that air in the system will cause that code. Started freaking out when that came up three times in two days. Sigh.

Tried the air conditioning on Saturday. The extra air flow drops the temps to 200 in nothing flat at idle but still can't drive with the air on. The extra load is just a bit too much.

I've REALLY got to work on getting cool air into the intake. This 90-100 heat wave thing sucks.

Took it up wheeling again on Saturday. Blew the line to the air tank. Idiot at the exhaust shop melted it while doing the down pipes from the manifolds. Seriously. Is it THAT HARD to look at what's behind what you welding?!?!!???

Otherwise, all was good. Temps were down in the 70s so the it was hanging around 200-212 with no problems. Mostly it just parked at 206 and stayed there until we started on the long down hill stretches.

Edward

Dunno how it works. Never really looked into it. On second thought, it may not be a good idea at all. If the water moves too fast, it won't hang out in the radiator long enough to scrub off enough heat. Akin to having no thermostat...

Don't mind me... <img src="/forums/images/graemlins/ignore.gif" alt="" />

I have never seen a problem with water flow in a 6Gx waterpump.
The Mercedes auxiliary waterpump I an aware of is to provide flow to the heater core.

I do not see water flow being Edwards problem here, he simply does not have a radiator that cools his engine. The change he has in process will be noticeable.
The only other change I would consider is an active vent from the bleeder on top of the thermo housing to the low pressure side of the radiator. I install crossflow radiators so the vent is easy to incorporate. This way any gasses that form in the system are not trapped and blocking flow.

In a proper loop system, as long as circulation rate is sufficient, I would think the time coolant spends in the heat transfer stage is not important, since any heat transfer lost by rapid cycling is made up for by re-entering the cooling vessel more often. As an example, if short cycle time resulted in lower heat transfer, the engine would overheat at higher rpm and remain cool at idle.

Given an otherwise healthy system - including a free-flowing radiator - inadequate cooling is more likely the result of insufficient heat transfer surface area, insufficient coolant capacity or insufficient air flow to move heat away from the heat exchanger (radiator). Less likely, but possible, could be plugged engine cylinder water jackets.

Inadequate air flow can be the result of poor fan shroud design, bad fan clutch, incorrect fan cfm flow or inadequate fan speed.

Inadequate coolant flow at idle can be caused by a bad water pump or low engine idle speed, which if a mechanical engine fan is used, also reduces engine fan speed.

An electric fan should be ok at idle, unless the radiator fins are blocked, shroud design is improper, cfm is too low or low idle speed reduces voltage to the fan(s), causing a fan speed drop and cfm reduction.

I would try using the original shroud and fan with a good clutch and see if it corrects the problem..... but I'd also be thinking about a radiator with more capacity.

Frank