My 2000 Ford F-150 pickup has been at the dealership. They say the radiator has oil mixed with the water and it's real thick. Now the truck won't start and the battery is new. However, it will start when it is jumped. Dealership thinks it might be a blown headgasket, but would this keep it from starting? Once you get it started it will restart and sometime it won't, for example, if it sits. Again the battery has a full charge. Could the oil leak have anything to do with the vehicle not starting?

Thanks

Normally to check for a blown headgasket you would see bubbles and use a tester at the radiator for detection of exhaust gases. If your getting oil in the water and you have an automatic transmission you could have seepage internally when the radiator has a transmission cooler in it. The higher pressure from the transmission pumps oil into the radiator at the breech point causing the two parts to mix. You may just need a good flushing and radiator to to cure the oil in water or run an accessory oil cooler (external) for your transmission. If your doing a fair amount of towing I would recommend it anyway.

The starting problem can be from bad connections. What is happening when you attempt to start it with just the battery? Also are you getting an unusual amount of water coming from your exhaust ? Is there any water getting into your engine oil ?

I have noticed a lot of water coming from the exhaust. There is no water in the engine oil. When you attempt to start iti with just the battery, it barely turns over but the battery is fully charged. After it starts, it will usually start again.

I have noticed a lot of water coming from the exhaust. There is no water in the engine oil. When you attempt to start iti with just the battery, it barely turns over but the battery is fully charged. After it starts, it will usually start again.

As far as starting your going to need an amp tester to find out what the problem really is. If your starter is dragging then your going to need to find out why. It may just need replacing or there could be a bad connection along the way. Make sure your ground cable is clean at both ends and you have a solid ground. But first your going to need to find out what the issue is with the water / oil situation.

Califdadof3 is correct. You will need to assess the 'mixing' issue then assess the 'starting' issue. The may be related but you need to determine exactly where the mixing is occurring.
Like he said, if the radiator is contaminated but the engine oil isn't, you need to focus on looking for an internal (to the radiator) cooler, whether it's a trans cooler or an oil cooler.
If that internal cooler has even a pin-hole, it operates at far higher pressure than what is normally in the radiator. This allows contamination in the radiator that usually doesn't get noticed anywhere else but the radiator and overflow jug.
If the failure was the head gasket, you would likely see the engine oil contaminated with coolant since at the point of failure, the coolant is operating at higher pressure than the engine oil at the same location.
Are you seeing trans fluid or oil levels going low? Even slightly?
You may want to get a second opinion/diagnosis just to help clear up the actual failure.
Let us know.