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Cooling System Issues

How replacing your water pump can help you keep your cool

Dick Moritz Sep 22, 2005
0508_01z Chevrolet_Corvette Bolts 2/17

Start by loosening the water-pump-pulley bolts, then remove theserpentine belt and upper radiator hose.

Cooling systems seem simple until you get into BTUs, thermalconductivity, flow, cavitation, pressurization, heat of vaporization,and nucleate boiling. Whatever happened to adding antifreeze and hittingthe road?

Actually, nothing happened to these issues. They're still there, stillin charge of heat transfer in your car, and still the culprits thatcause boil-overs. But you don't have to be a genius in thermodynamics tounderstand the basics of your cooling system and learn some of the stepsyou can take to prevent overheating. While Corvette Fever may be a greatname for a magazine, it's a lousy condition to encounter in the middleof summer.

0508_02z Chevrolet_Corvette Airflow_Housing 3/17

Remove the mass airflow (MAF) housing and duct.

So here's the Cliff's Notes version of Cooling System 101:
* Engines generate heat.
* Cooling systems dissipate this heat.
* Bigger, more efficient cooling systems dissipate more heat.

Engine heat is a byproduct of combustion. Liquid in cooling systemspicks up heat from passages in the block and heads and carries itthrough a radiator that, obviously, "radiates" the heat into the airpassing through and around the fins and tubes and into the atmosphere.The water pump provides propulsion through the system. Because enginesare most efficient at a particular temperature range, a thermostatregulates the flow of coolant through the radiator to maintain aspecific nominal temperature: 195 degrees F in most Corvettes and otherlate-model cars and light trucks.

0508_03z Chevrolet_Corvette Connectors 4/17

Be careful with electrical connectors to avoid breaking the brittleplastic tangs. We broke one during disassembly and had to secure it witha small tie wrap.

We all know that water boils at 212 degrees F. Or does it? Actually, itdoes at atmospheric pressure. However, pressuring a vessel of waterraises its boiling point by roughly 3 degrees for every pound ofpressurization. So in a cooling system running with a 15-psi radiatorcap, pure water won't boil until: (212 + [15x3] = 212 + 45 = 257 deg.F).

Since steam is a terrible conductor of heat, it's far better to keep theold H2O in a liquid state, even at a super-heated temperature.

Factor in the effects of antifreeze, and you can raise the boiling pointof your coolant to something on the north side of 275 degrees F. Butyour engine would be a whole lot happier if you could keep the coolanttemperature down so you wouldn't need all this extra "anti-boiling"protection in the first place.

Parts List

(From Mid America Motorworks catalog)

* High Performance Water Pump, PN 611-131

* Serpentine Belt, PN 611-002

* Fan Switch, PN 609-106

* Low-Temp Conversion Harness, PN 609-108

* Water Wetter, PN 100-891

* 2 gallons of antifreeze

0508_04z Chevrolet_Corvette Diverter 5/17

It would be easy to miss this bolt that secures the diverter-valvebracket to the top of the water pump.

In this article, we'll cover theinstallation of a high-performance water pump, along with a couple ofextra tricks, all courtesy of the good folks at Mid America Motorworks(MAM) who recommend and provided the items discussed here.

The idea of a high-performance water pump is to move the maximum amountof coolant through the engine for picking up all those nasty BTUs andcarrying them through the radiator, which will handle the "radiating"task. The Edelbrock pump recommended by MAM features a larger and moreefficient impeller, as well as a computer-designed pump housing passagesto flow more coolant at a higher velocity, even at lower rpm. Otherfeatures include a heavy-duty ball/roller bearing for extended lifeunder severe operating conditions, a heavy-duty shaft seal, and a uniqueO-ring replacing the conventional gasket sealing the rear impellercover. The chrome-plated housing greatly improves underhood looks.

So how tough is it to change the water pump on a C4? Not too hard ifyou've got 3-4 hours, a standard complement of SAE and metric handtools(see sidebar), and some patience. Here's the deal.

0508_05z Chevrolet_Corvette Valve_Bracket 6/17

Note the orientation of the diverter-valve bracket to facilitatereassembly.

Start with the usual "disconnect battery negative cable" since theprocess involves the removal and reinstallation of a few electricalconnectors. Don't forget--you'll need to reset the radio presets andclock when you're done. You'll have to drain the coolant, then removethe upper and lower radiator hoses and heater hoses, the mass airflowsensor housing and duct, serpentine belt, belt tensioner, two airinjection control valves (officially called an Electric Divert Valve andan Electric Air Switching Valve if you're looking at a factory servicemanual), and the A/C compressor in order to gain access to the waterpump. It's also necessary to disconnect two fuel lines in order toremove the A/C compressor-mounting bracket, which is in the way ofwater-pump removal. All of this is pretty straightforward except for theA/C compressor, which can drive you batty if you don't know what to lookfor. The photos below will save your bacon on this.

A Little Extra Insurance

0508_06z Chevrolet_Corvette Belt_Tensioner 7/17

The belt tensioner incorporates an indexing tang. Be sure to properlylocate this tang in its slot during reassembly. The tang keeps thetensioner from rotating against the force of the belt.

After installing our high-performance water pump, we tapped the MAMcatalog for a new thermal switch for the electric cooling fans thatturns them on at a lower temperature. Our test car was factory equippedwith B4P dual cooling fans; MAM offers an auxiliary fan kit, PN 609-110,for C4s with only a single fan from the factory.

In a test before we started, we learned that the fans turned on whencoolant reached 219 degrees F, then turned back off when coolanttemperature dropped to 192 degrees F. We installed a switch that droppedthe ON threshold to 197 degrees F, then turned off when coolanttemperature reached 187 degrees F. The advertised switch points are 200degrees F and 185 degrees F, which suggests that either the calibrationof the switch was off by a degree or two or, more likely, that there's aslight inaccuracy of the digital readout in our C4.

Tricks Of The Trade

Here are a few tips to help keep you out of trouble on this water-pump replacement.

* Loosen the water-pump-pulley bolts before removing the serpentine belt. The tension on the belt will help keep the pulley from turning. Likewise, retighten the bolts after the belt is back on.

* Carefully pry back the retaining tangs when disconnecting the electrical connectors. All C4s are old enough for the plastic to be brittle. All of the connectors you'll be dealing with are made so they cannot be interchanged.

* Don't change the orientation of the hose clamps during reassembly; there will probably be something in the way during reassembly that will obstruct access.

* Remove the water pump's heater-hose nipple while the pump is still bolted to the engine. The engine does an excellent job holding the pump for you. The same goes during reassembly.

* Use a line (flare) wrench on the fuel-line fittings, and use a second wrench to hold the adapter fitting while loosening the connector fitting to prevent twisting.

* Use Teflon tape on the threads of the heater-hose nipple during reassembly to help prevent leaks.

* Apply some silicone sealant to the water-pump-mounting bolts that thread directly into coolant passages.

0508_07z Chevrolet_Corvette Compressor 8/17

This is the proper position for the Torx bolt hidden under theA/C-compressor clutch. The A/C compressor bracket mounts on the twowater-pump studs.

The electric fans are switched in two different ways. The auxiliary fanis switched by sensing coolant temperature, which is what we'readjusting here. The other (primary) fan is switched by way of the ECM.That circuit is probably superseded by our work since, presumably,engine-operating conditions will probably never reach the thresholdsprogrammed into the ECM. In fact, our new switch turns on both fanstogether.

The helpful folks at MAM recommended that we put in a bottle of Red LineWater Wetter, which increases the ability of the coolant to absorb heatfrom the engine and give it up through the radiator. This will help ourC4 keep its cool on those hot summer days when the dragstrip Christmastree is in our rearview mirror.

Finally, fill the radiator and bring the engine up to operatingtemperature with the radiator cap off, then install the cap, making surethe overflow bottle has the proper amount of coolant. Check the coolantlevel in the radiator (cold) for each of the first couple of days to besure it's at the proper level as pockets of air continue to bleed out.

0508_08z Chevrolet_Corvette Hidden_Bolt 9/17

Here's the hidden bolt you have to look for just below the A/Ccompressor clutch. This Torx bolt has a flat on one side of the head.During removal and reassembly, this flat must align with one of the twoslots in the compressor-clutch pulley, which can easily be turned byhand for proper alignment.

What's the bottom line? A significant difference for sure. On an 18-miledrive cycle that included cold startup, stop-and-go, and highwaydriving, we saw an overall reduction in average coolant-temperaturereadings of about 10 degrees. But perhaps the most dramatic differenceappeared in the highest temperature noted in our drive cycle, whichpeaked at 211 degrees indicated in traffic. After our cooling systemmods, the highest temperature we saw was 198 degrees F.

Tools Of the Trade

No unusual or special tools are needed for replacing the water pump and fanswitch on a C4, other than a T45 Torx socket. You can probably buy onlythis size for the job, but if you plan to do more work on your car youmight as well invest in a set--you'll probably need them sooner orlater. Tools used:

* Metric and SAE sockets (standard and deep-well) and combination wrenches: 8mm, 10mm, 13mm, 15mm, 1/2-inch, 9/16-inch, and 13/16-inch (for the fan switch)
* Universal joint
* Common screwdrivers
* T45 Torx socket
* 1/2-inch drive breaker bar (for loosening the belt tensioner)
* 16mm line wrench

So How Tough Was It?

It took us about 31/2 hours to replace the water pump and fan switch,including refilling the system. It's a good idea to have a helpereyeball wiring and hose routing, and for holding things out of the wayas you work.

Was this upgrade worth the effort? You bet.


Mid America Motorworks
Effingham, IL



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