brad-cam

I've also realized that the bypass seal in the water pump is important. Mine was worn with a couple chunks missing. I managed to get the old one out (it was a PITA), but I couldn't for the life of me get the new one in (with the WP in the car, there is basically no clearance for pressing a seal into the opening).

It was said above that freezing it to shrink it may help. I left it out entirely and the car runs in the middle of the gauge, sometimes moving up to just below the second white line.

I'm doing a WP and belts replacement soon, so I'll fix it then for sure. Any other hints for how to get the seal into the pump ? It seems like a very tight interference fit and the seal I bought from Performance had a metal core (encased in plastic - I cut it open).

Sam Lin

I've run my 951 in AZ without a thermostat since I got it, simply because the PO didn't have one in. I'll put one in eventually, but have not had any issues in the meantime.

Sam

sayporsha

Done this before on my 951 and just did it on my 968.

Getting the new seal in was a piece of cake: I pressed it in (by hand) with the butt end of a large socket. Didn't need to shrink it.

Getting it out was the PITA. I hooked it with the head of a nail held with Vise Grips. Used a pry bar against the water pump to pull it out. Work your way around it to keep it from binding - it has a metal ring molded inside the rubber. Use a mirror to look inside the pump and make sure you get all the chunks out.

Tom M'Guinn

Just for the record, I ended up pulling out the thermostat in the summer (miami, always warm), to buy some time to drill a thermostat. I did not plug the rear bypass area, and the car runs exceptionally cool now. This morning, for example, it as bitter winter for south florida (maybe 60 degrees out), and on the freeway, I could barely get the water temp over the bottom white block. It ran well below the first white line all morning. When it gets warmer, it will warm up to the first white line and then the first fan kicks on and it pretty much stays at the first white line. The car has never run cooler. (I replaced the radiator, sender, pump, hoses, resivoir, etc. previously, chasing the hot temp problem.)

TonyG

Guys...

Unless you are making over 400RWHP in race trim, you will not have a problem cooling your car with the stock radiator.

If the stock radiator is good (and by good... I don't mean "well... it doesn't leak..."), a cooler temperature thermostat, and your lower spoiler installed, your car will cool perfectly both on and off the track at ambient temperatures of 105F.

If you have cooling problems, you need to look at your radiator, your thermostat, make sure you have the bottom front spoiler installed, and possibly install a the lower temp thermostat.

That's it.

Do not run without the thermostat, and do not drill out anything.

Try a new radiator and thermostat.. :-)

TonyG

Tom M'Guinn

Everything in my system is new -- radiator, hoses, pump, coolant, thermostat, fresh head, sensors. I never intended to run without the thermostat, but took it out in desperation when the car would not cool in the humid Miami heat. I was very surprised how cool the car runs without the thermostat, given the discussion about the bypass and all. It actually runs too cool cruising on the highway unless the outside temp is 70 or higher.

Tony, why do you say not to drill it? Seems like that would improve flow a bit, allow trapped air to get out easier, and only slow warm up a little bit. What's the down side?

TonyG

Tom

Trapped air will always find its way up.... directly to the bleed screw which is the highest part in the cooling system.

To bleed, simply open up this screw, and use a hose on top of the radiator tank, pinch off the over flow line, and blow.

It's bleed pretty much as simple as that.

Did you check your radiator prior to installation to make sure that all the bosses were actually clear. It's been seen that new radiators sometimes can have casting flash (in plastic) that has been seen to actually block off the holes. Always check the bosses.

If you have a leaking head gasket, your water temps will rise real fast. A sure sign of a leaking head gasket.... which will usually only show itself under constant boost.

And removing the thermostat is a bad idea for many reasons..... just do a search in google. Drilling it out isn't going to cure your problem.

I run a lower temp thermostat. The reason is that I like to keep my temps down more towards 180F-190F rather than 210F-220F. The lower temp thermostat will do that.

Also a neat trick is to shunt the two sensor wires together off the radiator fan thermo switch. What this will do is to cause the fans to come on at high speed rather than low speed, then switch to high speed. The benefit is that the temps drop much faster once the fans come on in traffic.

Perhaps your thermostat was bad/defective?

I can tell you this.. in the Phoenix summer heat... 115F, my car ran cool with the a/c on in traffic and on the highway. At WSIR (race track) my car ran cool on a 110F ambient temp day (racing).

TonyG

Tom M'Guinn

I actually think I did get all the air out with and without the thermostat. I blow on the tank -- no gurgling sounds with the heater on.

I did check the rad. Also, the car runs super cool without the thermostat, so I'm pretty sure the radiator is ok.

My original overheating was due to the head gasket. When I replaced that the car stopped overheating, and ran within the white lines, but just ran closer to the top line more often than I would like. (I moved to Miami in the middle of the head gasket job, so the change is probably just the new hot HUMID weather -- but still, I like it running cooler.)

Despite what people say about lower temp thermostats not doing any good, I am inclined to try one. Also inclined to try your fan trick. Already have the lower temp rad sensor. When I had the thermostat installed I jumpered the fans on high, and it did help.

I tried 3 thermostats--one of them must have worked.

FYI, the car was not overheating, I just took out the thermostat to see if that was why the car was running so close to the top line so often.

Bones944

Actually removing the thermostat could INCREASE an overheating problem. With no restriction from the thermostat, the coolant could recirculate too quickly, thus spending less time in the radiator where it exchanges off the excess heat.

Tom M'Guinn

That certainly has not been my experience, although I have heard the theory before. Leaving the bypass open is also said to reduce cooling, since the waterpump can spin its wheels that way. All I know for sure is that my car has never run cooler, running below the first white line if the outside temp is lower than 70 or so, and running at the first white in the hottest whether. I seem to recall the Excellence article about Graham Gilles Powerhaus-built car saying that it ran without a therostat too, to keep cooler. It's not an all-weather solution, but at least I have confirmed that my system is capable of cooling well.

roadrunner

Where does this idea of coolant passing too quickly through the radiator and not being able to exchange heat, come from? The radiator already provides it's own restriction to flow, but if you further slow the flow through the radiator, you're also delaying the coolant inside the water jacket from reaching the radiator and that means the coolant is picking up additional heat from the engine; hence, higher coolant temperatures within the engine.

If you slow the coolant enough and it boils in the water jacket before reaching the radiator, your coolant will no longer be able to absorb enough heat to prevent a runaway overheating episode due to the air pocket displacing the coolant.

The coolant being diverted through an unblocked bypass, as you would see with no thermostat, would cause a larger heating effect. Again, the vaporizing coolant collecting within the engine rather than being forced to the radiator can cause a problem here. However, with a functioning thermostat blocking off the bypass, and if the coolant velocity is high enough, it could force the vapor past the high point at the bleeder and into the radiator, where it would most likely bleed itself out from the tube that goes back to the reservoir.

This idea of slowing the flow was demonstrated to be false in an IC engine class and lab when I was in school, the maximum heat flow went way down when the coolant flow rate in the radiator was slowed for given heat generation rate.

Tom M'Guinn

Roadrunner, your description is consistent with my experience. One question, with a sealed and fully vented system, how could water vaporize inside the block?

Alan C.

Wiring the fans together has worked for me as well. A little more noise but in my case it doesn't matter.

roadrunner

Tom,

Microboiling occurs at the coolant/cylinder wall interface, and the vapor bubbles are usually so small that they immediately condense back to liquid due to the sheer mass of coolant in contact with the bubble. The closer the mass of coolant gets to it's boiling point, the more bubbles will form. Eventually you'll get to a point where the amount of bubbles forming will be greater than the amount of bubbles condensing, and the reduced heat transfer and themal inertia of the vapor stuck in the block will lead to a runaway overheat situation.

This usually happens when there's a leak that reduces the system pressure and allows the coolant to boil prematurely, but it can also happen if the coolant flow is reduced too much. The heat energy flowing to the radiator can be slowed by slowing the coolant, but that doesn't slow the heat energy flowing from the combustion to the water jacket.

Tom M'Guinn

If the dash gauge says my motor is running cool, even without the thermostat installed, then I don't have to worry about this fancy book-learn'n stuff, right?