Stroker overheating

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YJLopes
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Stroker overheating

Post by YJLopes »

I have short rod 4.7 I built years ago. It's using stock 4.0 pistons because there wasn't much else available back then for reasonable money. I used a mild comp cam but I can't find my notes on the specs. I didn't deck the block because I had no idea about quench back then. It also has Ford 24# injectors, 99+ intake manifold, pacesetter long tube headers, and relocated IAT sensor.

It is installed in a 91 YJ with a chevy 700R4 behind it. It's overheating and I'm ready to pull this engine and go back to stock. The entire cooling system is new (radiator, derale electric fan, high flow thermostat, high flow thermostat housing, flowkooler pump, hoses), timing is stock, distributor index is correct.

It overheats anytime the engine is running over 25-2800 while cruising. It slowly creeps up to 230-240 before I get concerned and back out of it. Cruising around in 3rd gear at 60 it's turning 2800 rpm and will get up to 220 pretty quick. 80 MPH in 4th at 2800 RPM it will climb to 230+. I live in Denver and driving up I-70 in to the mountains and in 3rd gear at 60 there is plenty of power left but I have to back out of it because it will hit 240 in a hurry.

All of the temps described are from a digital autometer gauge with a sending unit installed in the factory location.

I installed a wideband to see if it was running lean. In the cruising conditions described above it was running 14.6-14.8 until it downshifted to maintain speed on a hill. Then it may drop to 12.5-13.

Would an adjustable map sensor save the day?

Any ideas? I've been fighting this for a long time and just living with it by taking it easy, but I just convinced something isn't right, just not sure where to go from here.
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Re: Stroker overheating

Post by YJLopes »

I forgot a few details.

I checked the coolant for combustion byproducts, none found so I'd like to think the head and head gasket are okay.

It's running on a 50/50 mix with water wetter which seemed to help by 3-5 degrees.

I read of a few cases with similar symptoms where the head was replaced and solved the problem. I'm still trying to wrap my head around the idea that a head could be cracked and not have coolant in the oil or combustion chamber.

I ran a stock cooling system and had the same issues. Mostly new parts there as well (radiator, thermostat, fan clutch).

Full disclosure, I have AC and a winch that are probably not helping. I also have a transmission cooler but that seemed to help when I installed that by providing another heat sink.

The lockup in the converter is working properly as well.

I checked for a plugged cat and it was fine.
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SkylinesSuck
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Re: Stroker overheating

Post by SkylinesSuck »

Stock 4.0 pistons on 4.2 rods and crank? And no decking of the block?
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Re: Stroker overheating

Post by YJLopes »

SkylinesSuck wrote:Stock 4.0 pistons on 4.2 rods and crank? And no decking of the block?
Yep, piston ends up .0225" lower in the bore if I remember right. Obviously not ideal, but I didn't know better 15 years ago.
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Re: Stroker overheating

Post by Cheromaniac »

SkylinesSuck wrote:Stock 4.0 pistons on 4.2 rods and crank? And no decking of the block?
Mine was essentially the same and it never overheated so that isn't the issue.
Since his engine only runs hot at highway speeds, there's either insufficient airflow through the radiator (winch could be blocking it) or insufficient coolant flow. I doubt it's the latter so my money's on the former. See if the problem is resolved by removing the winch.
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YJLopes
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Re: Stroker overheating

Post by YJLopes »

Cheromaniac wrote:
SkylinesSuck wrote:Stock 4.0 pistons on 4.2 rods and crank? And no decking of the block?
Mine was essentially the same and it never overheated so that isn't the issue.
Since his engine only runs hot at highway speeds, there's either insufficient airflow through the radiator (winch could be blocking it) or insufficient coolant flow. I doubt it's the latter so my money's on the former. See if the problem is resolved by removing the winch.
I removed the winch and bumper and it improved things by around 4-5 degrees, but it still gets hot. 85-90 degree day, I'll see 215-220 cruising at 60 in 3rd gear, as soon as I start climbing in to the mountains it will get to 240 in a hurry.

Any concern with those AFR's?
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Re: Stroker overheating

Post by Cheromaniac »

The AFRs look fine. When did you last replace the lower radiator hose? Just wondering if the spring inside it has rotted away and the hose is collapsing.
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Re: Stroker overheating

Post by YJLopes »

Cheromaniac wrote:The AFRs look fine. When did you last replace the lower radiator hose? Just wondering if the spring inside it has rotted away and the hose is collapsing.
New hose in the last few months, no sign of it collapsing while running it the shop up to 3000-3500 while hot.

I spoke to a machine shop this morning about cleaning up an extra head I have in the shop. We discussed this issue and he said he had a similar problem with a similar build in his own XJ years ago. It turned out to be the cam. My engine has 55k on it, so I think I'm going to pull the valve cover (its leaking anyway) and put a dial indicator on the rockers.
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Re: Stroker overheating

Post by jsawduste »

Factory parts, not OEM replacement parts but genuine factory OEM Mopar parts are all I use.

With that recipe I`ve never had a customer or my own have any overheating issues.

In that last week I've put over 500 miles in 85/90 ambient running on the freeway at 75/80 mph. 2800/3200 rpm and 210*

On a YJ with 37`s, winch and a PS cooler in front of the radiator. Within a moment or two the temp drops back to 195 ish.

None of the YJ hoses ever have springs in them.

Id dump the fancy dancy parts and go back to fresh stock components. Know you said it was over heating with stock parts. Were they Mopar parts or stock replacements ? Had the radiator been properly rebuilt ?
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Re: Stroker overheating

Post by YJLopes »

I think I figured it out last night. The cam is junk. Every love I checked was down to less than .400 lift and several were in the .325-.-350 range. I don't remember all of the specifics of this cam, but I do remember the lift being in the .440-.450 range.
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Re: Stroker overheating

Post by SkylinesSuck »

How did you check the lift? Did you have a bunch of sparkles in your oil?
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Re: Stroker overheating

Post by YJLopes »

SkylinesSuck wrote:How did you check the lift? Did you have a bunch of sparkles in your oil?
No sparkles, but I believe this wear happened over time. The engine has 55K on it since I built it.

I checked the lift with a dial indicator on the rocker. I turned the engine until the valve was all the way open, watched the indicator until the lifter stopped bleeding down, turned until I was on the base of the lobe, reset dial indicator to zero, turned engine until the dial indicator peaked, wrote down number.
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