My 1994 Ford Van 351 is overheating. During the winter I took out the thermostat and put a new fan clutch in. Now I am trying to figure out if it is water pump or dirty radiator cores? Has anyone every had a water pump stop pumping water? The usual failure is the seals go out and water is leaking out, at least my experience. I am guessing a radiator flush isn't usually much good if you got this type of problem? This van has 75K on it.

 

It's hard to condemn a water pump that has no play in it. Shaft doesn't wobble? There are cases where the impeller has eroded away to the point that it cavitates and can't build up flow.

Before you go taking it apart, you might do well to get a radiator shop to do a sniffer test or get a chemical 'block check' from NAPA, to make sure you have not combustion leakage into the cooling system.

I know it's hard to see in a van but check your lower hose. Make sure it is rigid enough that it can't collapse when the water pump is sucking. Not all that rare.

And an easy check on the radiator, (if you can reach it,) when the engine is warmed up, just feel all over the surface of the radiator, looking for hot and cold areas. If you find both, it is plugged up. It should be a fairly uniform temp.

By the way, you should ALWAYS run a 190-195* thermostat.

 

Now when you say it's overheating, what are you basing that on?
I had 2 problems. One is that the temp sender, probably more specifically the plug going to it, was bad and it would just go up and down.

Second is that's a one-wire sender, the current returns through the engine block then through the engine's ground strap. It's possible that voltage drops from other devices on that path can increase the readings, especially if the ground isn't too good. I noticed my gauge immediately moves up most of a letter on the gauge when I turn on the heater/A/C blower alone, without turning on the A/C (which of course can increase temps).

What color antifreeze do you have?

 

It's either the water pump or some of the radiator core is plugged.

I live in SW Arizona and am the third owner of my 81 E100, I 6/300 van (all stock) a former water delivery van. Got it November 2004 from some friends who were going to convert it but had to sell it instead. (The engine was checked over, tranny was too and a new rear seal was put in but they did not check out other parts yet....but told me what was and not done). Changed the water after getting it and put in antifreeze.

It drove fine in the winter but as last Summer was coming on, it would overheat. Checked the waterpump...fine. Went to check the thermostat to find it was gone. The original owner had taken it out while using it as a delivery van from Phoenix to ShowLow sometime in it's past. I had already replaced the hoses but checked the radiator more thoroughly as the overheating was getting worse. Found some of the core was plugged up.

I wanted to get a new radiator as it looked pretty old (probably original and "beat") but my husband wanted to flush and try "rodding it" first. Flushed it without result. eventually it sprang a couple of small holes. StopLeak did not work. Finally my husband took it off to carefully "rod" the plugged slots. The core proved too rotten to do this effectively and fall apart when he tried soldering any holes.

I put my foot down and bought a new radiator. No more overheating problems.

 

What did a new radiator cost? Can't they recore the old ones?

 

About $200-$250. Not a lot of reason to try to repair the core.

 

My 88 F250 7.5L 460 had a plastic radiator.After eight years it cracked down the side.Replaced it with a metal one.

 

Never simply remove a T-stat, that is the dumbest attempt to fix overheating, it's redundant, the job of it is not onlt to keep fluid in the engine till it reaches operating temp, but to slow the flow, allowing it to stay at the correct temp and allow the coolant enough time in the radiator to cool, without it goes round and round without a cool down.
My father in law had the same overheating problem with a Ranger 4 banger, turned out to be the radiator, 2 gallons would fill both engine and radiator, found this after pulling it apart to replace hoses and head.

 

I was lucky. A local car parts store (Parker Auto) had a radiator for well under $200. Had it in stock for quite some time and still in the box unopenned. Just not much call for one. The Autozone here wanted far more and would have had to order it.

Unless you have an older truck with an all steel/brass radiator the new ones are mostly aluminum/plastic. You cant rod those, of course and most will just spend the money for a new one. My husband has rodded radiators before with success. But all of our daily vehicles are no older than 1986 with the oldest a 78. You can work on those radiators.

Just mine was too "shot" (one of the hose fittings was rotting too) to mess with.

 

Probably a combination of plugged radiator and no thermostat. Maples is right, part of the t-stat's job is to actually restrict water flow. Without it the fast moving water doesn't pick up as much heat. Even in race engines where you don't use a thermostat, a restrictor plate or gutted t-stat is put in its place.

Don't bother trying to repair or flush your radiator, much better/cheaper in the long run to replace it. There are several good mail order radiator distributors that will ship one to your door for $50-$100 less than you'd pay at most local places. Just got a new radiator for my van and paid $127 [shipped, no tax] from discountradiator.com, same part locally would have cost me $190. I'd also check arroheadradiator and radiatorexpress, have had good luck with them in the past for other vehicles.

 

Think of coolant on a molecular level as it flows through the block, heads and the radiator. The layer of molecules against the metal experiences drag so it moves slowly. The next layer moves a little faster and the next faster still. Each successive layer moves faster than the one below it until you get to the middle of the passage, furthest from the drag of the wall. This situation provides very poor heat dissipation. This is laminar flow.

Accelerating the flow combats the problem of poor heat exchange. Speeding up the flow creates, more turbulence putting more of the molecules in contact with the tube wall where the heat is dissipated better. Another way of creating turbulence is to use dimpled tubes, which also helps to break up the laminar flow.

This principle also has to be kept in mind inside the cylinder heads where most of the heat is generated. If the circulation is a slow laminar flow in the hotter areas, particularly in the area of the exhaust ports and valve seats this is where trouble starts. When the engine is under load and those areas reach temperatures above the boiling point of the coolant the molecules of coolant in contact vaporize and create a layer of steam, which effectively insulates the metal from the coolant which creates a deteriorating condition. Too much steam allows the metal to get continually hotter, creating more steam which forces coolant out of the overflow and then you are into a serious overheating condition. The way to prevent this is to speed up the flow to generate turbulence, which will scrub away the steam bubbles while they are still at the molecular level. Cooling passages are, or should be designed to shoot high-speed jets of coolant directly onto the surfaces that tend to get hottest. You know that if you are towing and your engine begins to overheat, you pull over and run your engine at a very high idle. What you are doing by stopping is generating less heat. The fast idle rushes the coolant over the hot spots, scrubbing off the steam, which allows the hot spots to normalize. Everyone has had the experience of seeing someone stop and shut off an overheated engine and remove the radiator cap only to have the cooling system go into a nearly explosive boil over. In that case, they didn’t cool down the engine by running at fast idle, so once the coolant stops flowing, the hot spots create a mass of steam. Opening the pressure cap lowers the boiling point so even more coolant vaporizes, and boom. Second degree burns.

One technique that has been used to deal with the problem of hot spots in the heads is to replace the thermostat with a restrictor plate, which builds up the pump pressure inside the block and heads. Never do this. It works up to a point simply because it further increases the boiling point inside the engine. It is never a good idea. Coolant speed is the ideal cure. And every street engine needs the proper thermostat.

The steam from the hot spots, (and all IC engines have them,) are the reason that we have “degas” bottles in the cooling system. Or, “liquid/vapor separators,” or “surge tanks.” They help to insure that the steam is what gets ejected when the system is heat driven into an overpressure condition.

It is the common belief that the cure for a hot running engine is a radiator with more rows of tubes. It does work in some cases but not all. In an unmodified engine, the stock radiator is of adequate size. If the engine is running hot there is usually a defect that needs to be corrected.

In the event that a turbo is added, or other modifications are made that increase horsepower to any significant degree, the cooling system will require upgrades.

The first thing to consider is to go to a water pump that will increase the flow. When a high volume pump is employed, it is a good idea to use a cross-flow radiator with the pressure cap in the tank on the low pressure side, (the side with the lower radiator hose attached.)

A well-designed fan shroud, as opposed to no fan shroud, can increase cooling effectiveness as much as fifty percent.

Also in the interest of airflow, moving any other coolers away from in front of the radiator will improve airflow and remove the heat load of the other coolers.

If you are running a turbo, devise air exits to get the heat out of the engine compartment. This also creates a more negative pressure behind the radiator, increasing efficiency.

If it proves necessary to increase radiator capacity, try to get one with a larger surface area rather than adding rows of tubes. Also, there are very effective high performance radiators available with one or two rows of deep tubes and louvered fins. These increase efficiency without adding 'rows.'

If you go from two rows to four rows, you double the volume flowing through it. If you double the volume, you reduce the rate of coolant flow through the radiator by half, getting back into laminar flow which reduces the heat dissipating ability by a large percentage.

 

Intresting discussion...let me provide more information. When I say it was overheating it is based on the gage going up over the mid point of the gage. I removed the thermostat and it did exactly the same thing with/without the thermostat! I have a F250 that was overheating(by the gage) and removal of the thermostat made that unit run very low on the gage all the time even in 120F days with a trailer load. The hot temp in the F250 was causing the transmission to run hot and dump fluid, all that stopped when I took the thermostat out. So I am not buying the argument that the thermostat actually makes these types of engines run cooler unless you can't depend on the gage to tell you the real conditions at all parts of the engine, which I supposed is possible. But we can get some data soon because I am pulling the radiator to have a flow test and if it is clogged I plan to have it rodded out for $75.

 

My radiator went bad,and i had to replace it real fast.All they had was a platic one.So i now have a plastic radiator.

 

The stock gauge is nothing more than a glorified idiot light. It sounds like you have a bad radiator in your F250 that's why it was overheating.

 

I used to be able to watch the coolant with the radiator cap off and rev the engine. If the water lowered or disappeared it showed that the pump was working, of course that depends on which direction the pump circulates the coolant too.