1. Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

Strange engine temp after switching oil weight

Discussion in 'Engine and Drivetrain/Mechanical' started by RagTop, Apr 17, 2017.

  1. RagTop

    RagTop Old Grumpy

    I live in the Sierra foothills, east of Sacramento, and the triple digit temps up here in the summer time were causing real problems for my mildly built 302. When the temperature got really high it would begin to lose oil pressure (I'm assuming the viscosity of the oil was being compromised). So I did my annual oil change last week and, on the advice of a friend, switched from Castrol 10W-30 to Kendall 20W-50. I hoped that would stop the oil from getting so thin in the hot weather. I took the car to a show this weekend and then out to burgers with my Mustang club. On the cruise the burger joint I wasn't looking at my gauges closely, but on my way home I looked down at my oil pressure and it was real high (I had the rebuilder replace the oil pump with a high volume model) so that was normal and positive. But then I looked over at the temp gauge and was shocked. In cool weather, like we had on Saturday, the car usually runs at about 1/3 the stock temp gauge scale. It was ticking along at about 2/3 of the scale and maybe 3/4 while I was on the highway. I actually started using my heater to dissipate some of the heat. When I got off the freeway the temp started to reduce to a range of 1/2 to 1/3 gauge. The last time I had a car that did this it was because the PO had overbored the engine excessively and it developed a pin hole in a cylinder wall. I checked my new oil to see if I had a chocolate milk shake in the crankcase and it was all clean and normal. It's got me worried that it might be a blown head gasket or a damaged block. My rebuild was 50K miles ago and it was overbored .040. Anyone have any suggestions as to what my trouble might be? It could be something as simple as a temp sender, but I doubt it since this coincided with the oil change. I guess I might have a stuck thermostat that is only partially open, but I doubt that too since the engine began cooling down after I got off the highway. Those puny Ford 20" radiators usually get overwhelmed after running at highway speed and not during. I am not going to replace my stock temp or oil pressure gauges with real devices, so my descriptions of "1/3 gauge" will have to suffice. Help!
  2. Horseplay

    Horseplay Well-Known Member

    The problem with old stock gauges is you never really know where things stand. I get you want originality so how about heading to Harbor Freight and getting a cheap infra-red temp sensor so you can at least get numerical temp values to give you a reference point. Take temps at a few distinct spots, I suggest at the thermostat housing, radiator tank and some other spot. Always use the same for all measurements. Now get it up to temp and see what 1/3 really means. Then hit the highway and when its up to 2/3 pull over and measure the same spots again. You may find the numeric temp value is perfectly normal/fine. May just be a gauge/sensor issue.

    If you had a blown head gasket you would have oil and water mix issues or at least leakage onto the garage floor. Not too mention you would have fluid loss from the radiator. You did verify the system is still full, right?

    FYI, high volume pumps are not a good idea for a stock/street engine. SBF don't need help in this area. At higher rpms you can actually pull all the oil out of the pan before any drains back. It's recommended to have a larger pan with added oil volume if going that route.
    6t6red likes this.
  3. 6t6red

    6t6red Well-Known Member

    When I built my mild 5.0 I stayed with a stock oil pump for the reason that Terry mentioned. I didnt want more oil in the valve covers than in the pan.
  4. RagTop

    RagTop Old Grumpy

    At the time I had the engine rebuilt I stayed away from high pressure pumps, but the rebuilder recommended the high volume unit. I've got an infrared temp gun in the trunk. I'll check the actual temperatures next time I take it out. My real concern is the odd way the car heats on the highway and cools back down on the street. Totally inverse to the way it is supposed to work. Air flow at highway speeds should aid in cooling and on the street the fan is all you've got.
  5. Midlife

    Midlife Well-Known Member Staff Member Moderator

    Yeah, unless your lower radiator hose starts collapsing or your water pump is beginning to go...
  6. RagTop

    RagTop Old Grumpy

    New water pump and no problems with the lower radiator hose. I did notice a latent miss from my engine under hard acceleration, initially, and now occasionally at highway speeds. Could a missing cylinder cause the car to overheat at speed but return to normal on city streets? Maybe I do have a wiring problem or maybe a problem with the almost twenty year old Pertronix Ignitor and Flame Thrower combination. Still also wondering about the possibility of a stuck thermostat. I guess I'll change the 160* that's in there for the correct 180* and see what happens.
    Last edited: Apr 19, 2017
  7. Horseplay

    Horseplay Well-Known Member

    Just because something is new doesn't mean it doesn't have problems. I seriously doubt you have a pump issue but it bears saying "new" doesn't mean "good". I've seen plenty of new parts that were defective/bad in my career. Double check everything when troubleshooting is a pretty basic premise.
  8. 3175375

    3175375 Well-Known Member

    Run Amsoil 20w50. I too have a 0.40 overbored 302 n it has always run hot. Saving bottles n cans for 331 stroker
  9. RagTop

    RagTop Old Grumpy

    Yeah, that's what I should have done back when I had the original engine rebuilt. That looks like a possibility because I found antifreeze in the drip pan that I keep under the car in the garage. This engine has never leaked a drop of anything in the 19 years I've owned it, so this is very unusual. Maybe it's only a head gasket or, even better, a leaky radiator hose. Quien sabe?? Guess I'll have to take it to the doctor.
  10. bartl

    bartl Old Fart

    Did you figure that "thicker" oil was going to REDUCE your engine temperature? a) the flow of oil throughout the engine removes heat. Higher viscosity slows flow. Less heat removed. b) more viscosity means the oil pump has to work harder. More work = more heat.
  11. RagTop

    RagTop Old Grumpy

    Nice theory, but why would racing oil be the heavier viscosity stuff if you're correct?
  12. bartl

    bartl Old Fart

    Because bearing clearances are so much wider to reduce parasitic power loss due to friction.
  13. zray

    zray who said Beer ?

    I have to go along with this article from the Melling (oil pump) website. Any over oiling to the to
    top end has nothing to do with the oil pump. Blocked drain holes, or stuck metering valves in the lifters are the main culprits of over oiling up top:

    Disclosure: I routinely use Mobil 1 15w-50 in all flat tappet classics. Phenomenal wear protection, and never any oiling issues, even when paired with high volume Melling oil pumps in my K codes and Shelby's. High volume pumps are not for everyone, the article gives a good list of situations where they are appropriate.


    Attached Files:

    Last edited: May 6, 2017

Share This Page