My '88 E350 big block 460cid runs great. The only problem is that when I'm driving on the highway the engine temp spikes. It hasn't overheated yet so I'm trying to find the answer to the question before it does. I don't have a lot of cash to just start replacing parts so I would like to try and get an answer before I start spending money. It does NOT run hot when idling or stopped at a red light, etc. Only when driving down the road. If I get it on the thruway for a ride, it will start to get hot but if I slow down and/or stop it will cool down. Any ideas?

 

Are you relying on your factory dash gauge?

My '87 E350 Diesel motorhome did that to. Untill I installed a real temp gauge. Reads 180* all the time! Even when my real gauge reads around 180* just cruising or off the highway, the dash gauge rides around O-R-M of NORMAL and the real one stays at the same place.


These old Fords, the dash gauges are garbage! Get a real one if you worryed about the temps.

 

Maybe the voltage spike of the alternator running faster is making your gauge act up.

 

Ditto on the gauge but also check your belt, I had a Cougar the did the same thing belt was slipping at highway speeds changed the belt problem solved.

regards

 

the water pump belt?

 

Yes in my case it was slipping at hi-speed and not moving enough water.

 

Also check for a mushy radiator hose that is collapsing, cuz the water pump is working harder at highway speeds.

 

I've had the temp gauge go wacky on my '82 E-350 460 V8 several times. The sending unit has been changed twice, and the connection to the sending unit was the culprit once too. The temp gauge pegs high rather than slowly climbing, so it was a fairly obvious electrical issue for me.

 

Where is the sending unit on that engine? Thanks

 

Well, mine's a carburetor 82, yours is an fuel injected '88, so there could be a difference. The temperature sending unit is screwed into the water passage on the top front of the engine. Look just below and to the right of the distributor cap. It looks like a big brass bolt with a wire coming off the top. Make sure the wire connection is tight. I've even used dielectric grease to make a better connection there.

 

I'll check that out. Thanks.

 

One more idea - the fan clutch. Not a high maintenance item, but worth a look. See that it's not covered in grease and fuzz, or leaking fluid out of the center.

 

okay, I'm getting fed up. Time to replace that stock water temp gauge. However I'm confused about the difference between "Mechanical" and "Electric". I think the sending unit for the old one is right next to the distributor cap, it's brass and has a plug popping out the top of it. So, which one do I buy? Mechanical or electric? And do I have to replace the sending unit? I just went for a lengthy drive today and the needle on the gauge was almost out of the normal range, it was right at the "L" of N O R M A L.

 

Sounds like you found your sending unit, which is electrical.

A mechanical temperature gauge is typically a non-powered style that has a threaded plug that goes where the stock electrical sending plug goes. It then has about a 6' capillary tube that goes to a gauge that you have to mount somewhere on your dash. I have not had much luck with those, but then I've always tried cheapo JC Whitney gauges. The electrical gauge (sending unit) is a direct replacement for your stock sending unit, and shouldn't be more than a few bucks (look them up on RockAuto.com to see what they look like).

Have you considered a radiator cleaning product? You've never answered us on all the totally worthy suggestions such as mushy radiator hoses or slipping belts. The thermostat can also be a culprit in all this.

 

I've changed the thermostat and didn't flush the radiator, but I did drain it and refill it. I think I'll probably try and do a thorough flush next time but I'll still try a new gauge just to get an accurate reading. I haven't tried new belts yet. That will be the next step. If that doesn't work then maybe I'll try a new water pump. I checked out the radiator hoses and they are pretty solid, they don't seem to have any mushy spots. However, when I run the truck and look in the radiator I don't really see water moving around so I wonder if I need a hi-flow water pump to get the water moving more. Thanks again for all the help and great suggestions.